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Assembly Source File | 1991-11-16 | 108KB | 2,499 lines

;--------------------------------------------------------------------------; ; Program: Recall .Asm ; ; Purpose: Commandline editor and history TSR. ; ; Notes: Compiles under TURBO Assembler, v2.0. Requires DOS v2.xx ; ; or higher. Editing keys are coded as PC extended scan ; ; codes; otherwise, this uses only DOS calls. ; ; The overall design is derived from RDE (aka, Rainbow DOS ; ; Editor) by Joe Kneidel. The methods used to install and ; ; uninstall this TSR are from _MS-DOS Developer's Guide_, ; ; by Angermayer and Jaeger. ; ; Status: Released into the >>>public domain<<<. Enjoy! If you use ; ; it, let me know what you think. You don't have to send ; ; any money, just comments and suggestions. ; ; Updates: 24-Oct-90, v1.0a, GAT ; ; - initial version ; ; 28-Oct-90, v1.0b, GAT ; ; - renamed get_LineFromUser to get_CmdLine and ; ; add_LineToBuffer to store_CmdInBuf. ; ; - made sure to zero out CH in add_LineToBuffer. ; ; - excluded CR from byte count in get_CmdLine. ; ; - kept track of CurCmd rather than PrevCmd/NextCmd and ; ; moved checks on command from recall_CmdFromBuf to ; ; mov_pcmd and mov_ncmd. ; ; - specified command table as an array of structures and ; ; revised ways it was accessed in get_CmdLine. ; ; - rearranged various procedures. ; ; - spruced up comments. ; ; 31-Oct-90, v1.1a, GAT ; ; - removed notices about preliminary notices. ; ; - cleanup up help message a bit. ; ; - avoided use of LABELs. ; ; - added list_CmdLines to list recall buffer contents. ; ; 10-Nov-91, v1.2a, GAT ; ; - caught and fixed bug involving DOS input redirection ; ; which caused 0Ah characters to remain in commandline. ; ; - revised include file names. ; ; - added pseudo-environment so program name will show up ; ; with things like PMAP, MANIFEST, and MEM. ; ; - uses INT 2D as per Ralf Brown's Alternate Multiplex ; ; Interrupt proposal. ; ; - shares interrupts as per IBM's Interrupt Sharing ; ; Protocol. ; ; 16-Nov-91, GAT ; ; - made minor changes in return values from the Int 2d ; ; handler to track Ralf's proposal. ; ;--------------------------------------------------------------------------; ;--------------------------------------------------------------------------; ; Author: George A. Theall ; ; Phone: +1 215 662 0558 ; ; SnailMail: TifaWARE ; ; 506 South 41st St., #3M ; ; Philadelphia, PA. 19104 USA ; ; E-Mail: theall@gdalsrv.sas.upenn.edu (Internet) ; ;--------------------------------------------------------------------------; %NEWPAGE ;--------------------------------------------------------------------------; ; D I R E C T I V E S ; ;--------------------------------------------------------------------------; DOSSEG MODEL tiny IDEAL LOCALS JUMPS ; ; This section comes from Misc.Inc. ; @16BIT EQU (@CPU AND 8) EQ 0 @32BIT EQU (@CPU AND 8) MACRO ZERO RegList ;; Zeros registers IRP Reg, <RegList> xor Reg, Reg ENDM ENDM ; ; This section comes from DOS.Inc. ; BELL EQU 7 BS EQU 8 TAB EQU 9 CR EQU 13 LF EQU 10 ESCAPE EQU 27 ; nb: ESC is a TASM keyword SPACE EQU ' ' KEY_F1 EQU 3bh KEY_F2 EQU 3ch KEY_F3 EQU 3dh KEY_F4 EQU 3eh KEY_F5 EQU 3fh KEY_F6 EQU 40h KEY_F7 EQU 41h KEY_F8 EQU 42h KEY_F9 EQU 43h KEY_F10 EQU 44h KEY_HOME EQU 47h KEY_UP EQU 48h KEY_PGUP EQU 49h KEY_LEFT EQU 4bh KEY_RIGHT EQU 4dh KEY_END EQU 4fh KEY_DOWN EQU 50h KEY_PGDN EQU 51h KEY_INS EQU 52h KEY_DEL EQU 53h KEY_C_F1 EQU 5eh KEY_C_F2 EQU 5fh KEY_C_F3 EQU 60h KEY_C_F4 EQU 61h KEY_C_F5 EQU 62h KEY_C_F6 EQU 63h KEY_C_F7 EQU 64h KEY_C_F8 EQU 65h KEY_C_F9 EQU 66h KEY_C_F10 EQU 67h KEY_C_LEFT EQU 73h KEY_C_RIGHT EQU 74h KEY_C_END EQU 75h KEY_C_PGDN EQU 76h KEY_C_HOME EQU 77h KEY_C_PGUP EQU 84h KEY_F11 EQU 85h KEY_F12 EQU 86h KEY_C_F11 EQU 89h KEY_C_F12 EQU 8ah DOS EQU 21h ; main MSDOS interrupt STDIN EQU 0 ; standard input STDOUT EQU 1 ; standard output STDERR EQU 2 ; error output STDAUX EQU 3 ; COM port STDPRN EQU 4 ; printer TSRMAGIC EQU 424bh ; magic number STRUC ISR Entry DW 10EBh ; short jump ahead 16 bytes OldISR DD ? ; next ISR in chain Sig DW TSRMAGIC ; magic number EOIFlag DB ? ; 0 (80) if soft(hard)ware int Reset DW ? ; short jump to hardware reset Reserved DB 7 dup (0) ENDS STRUC ISRHOOK Vector DB ? ; vector hooked Entry DW ? ; offset of TSR entry point ENDS STRUC TSRSIG Company DB 8 dup (" ") ; blank-padded company name Product DB 8 dup (" ") ; blank-padded product name Desc DB 64 dup (0) ; ASCIIZ product description ENDS GLOBAL at : PROC GLOBAL errmsg : PROC GLOBAL ProgName : BYTE ; needed for errmsg() GLOBAL EOL : BYTE ; ditto GLOBAL fgetc : PROC GLOBAL fputc : PROC GLOBAL fputs : PROC GLOBAL getchar : PROC GLOBAL getdate : PROC GLOBAL getswtch : PROC GLOBAL gettime : PROC GLOBAL getvdos : PROC GLOBAL getvect : PROC GLOBAL isatty : PROC GLOBAL kbhit : PROC GLOBAL pause : PROC GLOBAL putchar : PROC GLOBAL setvect : PROC GLOBAL sleep : PROC GLOBAL find_NextISR : PROC GLOBAL find_PrevISR : PROC GLOBAL hook_ISR : PROC GLOBAL unhook_ISR : PROC GLOBAL free_Env : PROC GLOBAL fake_Env : PROC GLOBAL check_ifInstalled : PROC GLOBAL install_TSR : PROC GLOBAL remove_TSR : PROC ; ; This section comes from Math.Inc. ; GLOBAL atoi : PROC GLOBAL atou : PROC GLOBAL utoa : PROC ; ; This section comes from String.Inc. ; EOS EQU 0 ; terminates strings GLOBAL isdigit : PROC GLOBAL islower : PROC GLOBAL isupper : PROC GLOBAL iswhite : PROC GLOBAL memcmp : PROC GLOBAL strchr : PROC GLOBAL strcmp : PROC GLOBAL strlen : PROC GLOBAL tolower : PROC GLOBAL toupper : PROC VERSION equ '1.2a' ; current version of program ; nb: change TSR_Ver too! ; BUFSIZE specifies size of the recall buffer for collecting commandlines. ; Values of 255 or below are risky because that's the maximum buffer size ; for subfunction 10 of Int 21h and my code in add_LineToBuffer does not ; make sure commandlines will fit. I foresee no problems, however, with ; larger values up to about 60K. BUFSIZE equ 1024 ; >>>CHANGE AT YOUR RISK<<< ERRH equ 1 ; errorlevel if help given ERRINS equ 10 ; errorlevel if install failed ERRUNI equ 20 ; errorlevel if uninstall failed ERRNYI equ 25 ; errorlevel if not yet installed OFF equ 0 ON equ 1 %NEWPAGE ;--------------------------------------------------------------------------; ; C O D E S E G M E N T ; ;--------------------------------------------------------------------------; CODESEG ORG 0 ; address of code segment start SegStart DB ? ; used in when installing ORG 80h ; address of commandline CmdLen DB ? CmdLine DB 127 DUP (?) ORG 100h ; start of .COM file STARTUPCODE jmp main %NEWPAGE ;--------------------------------------------------------------------------; ; R E S I D E N T D A T A ; ;--------------------------------------------------------------------------; TSR_Sig TSRSIG <'TifaWARE', 'RECALL ',\ 'commandline editor and history TSR'> TSR_Ver DW (2 SHL 8) + 1 ; (minor shl 8) + major MPlex DB ? ; multiplex ID HookTbl ISRHOOK <21h, do_Int21> ISRHOOK <2dh, do_Int2D> ; 2d must be last!!! OldAX DW ? ; value of AX register when my ; handler is first called OldStack DD ? ; address of caller's stack CurCmd DW 0 ; pointer to current command ; in recall buffer InsMode DB ON ; InsertMode toggle flag STRUC CMD ; structure for editing cmd Key DB ? ; extended code for key Function DW ? ; address of editing function ENDS CmdTbl CMD <KEY_LEFT, OFFSET mov_lchar> CMD <KEY_RIGHT, OFFSET mov_rchar> CMD <KEY_PGUP, OFFSET mov_lword> CMD <KEY_PGDN, OFFSET mov_rword> CMD <KEY_HOME, OFFSET mov_bol> CMD <KEY_END, OFFSET mov_eol> CMD <KEY_UP, OFFSET mov_pcmd> CMD <KEY_DOWN, OFFSET mov_ncmd> CMD <BS, OFFSET del_lchar> CMD <KEY_C_LEFT, OFFSET del_lchar> CMD <KEY_DEL, OFFSET del_rchar> CMD <KEY_C_RIGHT, OFFSET del_rchar> CMD <KEY_C_PGUP, OFFSET del_lword> CMD <KEY_C_PGDN, OFFSET del_rword> CMD <KEY_C_HOME, OFFSET del_bol> CMD <KEY_C_END, OFFSET del_eol> CMD <ESCAPE, OFFSET del_line> CMD <KEY_C_F9, OFFSET del_buf> CMD <KEY_INS, OFFSET toggle_InsMode> CMD <0, OFFSET ring_Bell> ; >>>must be last<<< %NEWPAGE ;--------------------------------------------------------------------------; ; L O C A L S T A C K ; ;--------------------------------------------------------------------------; DB 16 dup("STACK ") ; 128 bytes for local stack StackTop = $ %NEWPAGE ;--------------------------------------------------------------------------; ; R E S I D E N T C O D E ; ;--------------------------------------------------------------------------; ;---- is_CharWhite ------------------------------------------------------; ; Purpose: Tests if character is either a blank or a tab. ; ; Notes: none ; ; Entry: AL = character to be tested. ; ; Exit: Zero flag set if true, cleared otherwise. ; ; Calls: none ; ; Changes: flags ; ;--------------------------------------------------------------------------; PROC is_CharWhite cmp al, SPACE ; if == SPACE then zf = 1 jz SHORT @@Fin cmp al, TAB ; if == TAB then zf = 1 @@Fin: ret ENDP is_CharWhite ;---- get_KeyNoEcho -----------------------------------------------------; ; Purpose: Reads key from STDIN, waiting as necessary. ; ; Notes: Allows DESQview to operate efficiently if task inactive. ; ; Ctrl-C and Ctrl-Break generate Int 23h. ; ; Entry: n/a ; ; Exit: AL = character (0 => extended code available next). ; ; Calls: none ; ; Changes: AX ; ;--------------------------------------------------------------------------; PROC get_KeyNoEcho mov ah, 8 int DOS ret ENDP get_KeyNoEcho ;---- ring_Bell ---------------------------------------------------------; ; Purpose: Rings the console bell as a warning to user. ; ; Notes: none ; ; Entry: n/a ; ; Exit: n/a ; ; Calls: none ; ; Changes: none ; ;--------------------------------------------------------------------------; PROC ring_Bell push ax dx mov ah, 2 mov dl, BELL int DOS pop dx ax ret ENDP ring_Bell ;---- display_Char ------------------------------------------------------; ; Purpose: Displays character on STDOUT and advances to next char. ; ; Notes: Do *not* call this procedure to display backspaces; use ; ; backup_Cursor instead. Though they'd be displayed ; ; properly, BX would be *incremented* here. ; ; Does *not* adjust CH or CL. ; ; Entry: AL = character to display, ; ; BX = pointer to current position in commandline. ; ; Exit: BX++ ; ; Calls: none ; ; Changes: BX ; ;--------------------------------------------------------------------------; PROC display_Char push ax dx mov dl, al mov ah, 2 int DOS inc bx ; move to next char on cmdline pop dx ax ret ENDP display_Char ;---- advance_Cursor ----------------------------------------------------; ; Purpose: Moves the cursor forwards on the screen. ; ; Notes: none ; ; Entry: BX = pointer to current position in commandline, ; ; CH = # of bytes to end of line, ; ; SI = # of bytes to advance. ; ; Exit: BX += SI, ; ; CH -= SI. ; ; Calls: display_Char ; ; Changes: AX, CH, ; ; BX (display_Char) ; ;--------------------------------------------------------------------------; PROC advance_Cursor or si, si ; anything to skip over? jz SHORT @@Fin ; Adjust CH now. (This could be left until later - no big deal.) mov al, ch ZERO ah sub ax, si mov ch, al ; CH -= SI ; Display SI characters on commandline. push cx mov cx, si @@NextChar: mov al, [bx] call display_Char ; nb: increments BX too loop SHORT @@NextChar pop cx @@Fin: ret ENDP advance_Cursor ;---- backup_Cursor -----------------------------------------------------; ; Purpose: Moves the cursor backwards on the screen. ; ; Notes: Does *not* handle properly line-wrapping yet. ; ; Entry: BX = pointer to current position in commandline, ; ; CH = # of bytes to end of line, ; ; SI = # of bytes to back up. ; ; Exit: BX -= SI, ; ; CH += SI. ; ; Calls: none ; ; Changes: AX, BX, CH ; ;--------------------------------------------------------------------------; PROC backup_Cursor or si, si ; anything to skip over? jz SHORT @@Fin ; Adjust BX and CH now. (This could be left until later - no big deal.) sub bx, si ; BX -= SI mov al, ch ZERO ah add ax, si mov ch, al ; CH += SI ; Back up cursor by displaying non-destructive backspaces. push cx dx mov ah, 2 mov cx, si mov dl, BS @@PrevChar: int DOS loop SHORT @@PrevChar pop dx cx @@Fin: ret ENDP backup_Cursor ;---- delete_Chars ------------------------------------------------------; ; Purpose: Deletes characters from commandline. ; ; Notes: No checks are done on SI's validity; ie, caller should ; ; ensure there are enough characters on line to delete. ; ; Entry: BX = pointer to current position in commandline, ; ; CH = # of bytes to end of line, ; ; CL = # of bytes left in commandline, ; ; SI = # of characters to delete. ; ; Exit: CH -= SI, ; ; CL += SI. ; ; Calls: display_Char, backup_Cursor ; ; Changes: CH, CL, SI, ; ; AX (backup_Cursor) ; ;--------------------------------------------------------------------------; PROC delete_Chars or si, si ; anything to delete? jz SHORT @@Fin ; Adjust CH and CL now while I have SI handy. At the same time ; I am also computing the number of characters to shift. mov al, cl ZERO ah add ax, si mov cl, al ; CL += SI mov al, ch sub ax, si mov ch, al ; CH -= SI push cx ; final values of CH and CL push ax ; used to back up cursor ; Shift CH - SI characters remaining on line to the left by SI characters. mov cx, ax ; CX = CH - SI jcxz SHORT @@Coverup ; skip if deleting to eol @@NextChar: mov al, [bx+si] mov [bx], al call display_Char ; nb: increments BX too loop SHORT @@NextChar ; Display spaces to overwrite chars remaining on line. @@CoverUp: mov al, SPACE mov cx, si @@NextBlank: call display_Char ; nb: increments BX too loop SHORT @@NextBlank ; Back up cursor to its location on invocation. pop ax ; CH - SI add si, ax ; SI += (CH - SI) call backup_Cursor ; nb: decrements BX too pop cx ; NB: BX will be incremented (CH - SI) + SI times by display_Char and ; decremented CH times by backup_Cursor so overall it won't change. @@Fin: ret ENDP delete_Chars ;---- add_CharToLine ----------------------------------------------------; ; Purpose: Adds a character to commandline buffer. ; ; Notes: Checks to see if buffer would overflow first. ; ; Entry: AL = character to add, ; ; BX = pointer to current position in line, ; ; CH = number of characters until end of line, ; ; CL = number of bytes left in line. ; ; Exit: BX and CX changed as appropriate. ; ; Calls: display_Char, backup_Cursor, ring_Bell ; ; Changes: AX, BX, CX ; ;--------------------------------------------------------------------------; PROC add_CharToLine ; Check for space unless insert mode is OFF *and* not at eol. cmp [cs:InsMode], ON je SHORT @@CheckForSpace or ch, ch jz SHORT @@CheckForSpace ; Overwrite existing character while in not at eol. mov [bx], al call display_Char ; nb: increments BX too dec ch jmp SHORT @@Fin @@CheckForSpace: or cl, cl jz SHORT @@Abort or ch, ch jnz SHORT @@AddWithShift ; At end of line. mov [bx], al call display_Char ; nb: increments BX too dec cl jmp SHORT @@Fin ; Add character and shift everything to right over by 1 position. @@AddWithShift: push cx dx mov cl, ch ; CH = chars to eol ZERO ch mov si, cx ; save for backing up inc cl ; but add 1 to display new char @@NextChar: mov dl, [bx] ; use DL as temporary storage mov [bx], al call display_Char ; nb: increments BX too mov al, dl ; recover previous char loop SHORT @@NextChar call backup_Cursor ; nb: decrements BX too pop dx cx dec cl jmp SHORT @@Fin @@Abort: call ring_Bell ; if out of space @@Fin: ret ENDP add_CharToLine ;---- find_StartofPrevWord ----------------------------------------------; ; Purpose: Locates start of previous word in commandline. ; ; Notes: "Words" are delineated by blanks and/or start/finish of ; ; the commandline. ; ; Entry: BX = pointer to current position in commandline. ; ; Exit: SI = # of characters from BX to start of previous word. ; ; Calls: is_CharWhite ; ; Changes: AX, SI ; ;--------------------------------------------------------------------------; PROC find_StartofPrevWord push bx dx inc dx inc dx ; DX now points to bol mov si, bx ; SI = current position ; Skip over any whitespace. Note: don't bother with 1st character - ; think of how it should behave if positioned at start of a word. @@SkipWhite: dec bx cmp bx, dx jb SHORT @@Fin ; done if BX < bol mov al, [bx] call is_CharWhite jz SHORT @@SkipWhite ; Next skip over non-blanks until the start of the word. @@SkipWord: dec bx cmp bx, dx jb SHORT @@Fin ; done if BX < bol mov al, [bx] call is_CharWhite jnz SHORT @@SkipWord ; Finally compute how many characters must be skipped. @@Fin: inc bx ; backed up 1 too many sub si, bx pop dx bx ret ENDP find_StartofPrevWord ;---- find_StartofNextWord ----------------------------------------------; ; Purpose: Locates start of next word in commandline. ; ; Notes: "Words" are delineated by blanks and/or start/finish of ; ; the commandline. ; ; Entry: BX = pointer to current position in commandline. ; ; Exit: SI = # of characters from BX to start of next word. ; ; Calls: is_CharWhite ; ; Changes: AX, SI ; ;--------------------------------------------------------------------------; PROC find_StartofNextWord push bx dx mov dx, bx mov al, ch ZERO ah add dx, ax ; DX now points to eol ; Skip over any existing word. Note: unlike find_StartofPrevWord, here ; we do not want to initially skip ahead - imagine if cursor were at ; a blank before the start of a word. @@SkipWord: cmp bx, dx je SHORT @@Fin ; done if BX = eol mov al, [bx] inc bx call is_CharWhite jnz SHORT @@SkipWord ; Next skip over whitespace until the start of the word. @@SkipWhite: cmp bx, dx je SHORT @@Fin ; done if BX = eol mov al, [bx] inc bx call is_CharWhite jz SHORT @@SkipWhite dec bx ; point back to white space ; Finally compute how many characters must be skipped. @@Fin: mov si, bx ; where we are now pop dx bx sub si, bx ; less where we started from ret ENDP find_StartofNextWord ;---- recall_CmdFromBuf -------------------------------------------------; ; Purpose: Replaces current with a commandline from buffer. ; ; Notes: Does *not* check SI's validity. ; ; Entry: BX = pointer to current position in commandline, ; ; CH = # of bytes to end of line, ; ; CL = # of bytes left in commandline, ; ; SI = pointer to command in recall buffer. ; ; Entry: BX = pointer to end of new commandline, ; ; CH = 0, ; ; CL = # of bytes left in new commandline. ; ; Calls: del_line, display_Char, ring_Bell ; ; Changes: AL, BX, CH, CL, SI ; ;--------------------------------------------------------------------------; PROC recall_CmdFromBuf ; Clear current commandline and display new one. push si ; since del_line zaps SI call del_line ; changes CH and CL such that CX ; == max # of chars in buffer pop si @@NextChar: mov al, [cs:si] cmp al, CR je SHORT @@Fin inc si mov [bx], al call display_Char ; nb: increments BX too loop SHORT @@NextChar ; continue as long as CX > 0 cmp [BYTE cs:si], CR ; did loop end prematurely? je SHORT @@Fin ; no call ring_Bell ; yes, warn user @@Fin: ret ENDP recall_CmdFromBuf ;---- mov_lchar ---------------------------------------------------------; ; Purpose: Moves cursor left in the commandline. ; ; Notes: none ; ; Entry: BX = pointer to current position in commandline, ; ; CH = # of bytes to end of line. ; ; Exit: BX--, ; ; CH++, ; ; SI = 1 (or 0 if already at bol). ; ; Calls: backup_Cursor ; ; Changes: SI, ; ; BX, CH (backup_Cursor) ; ;--------------------------------------------------------------------------; PROC mov_lchar mov si, bx sub si, dx cmp si, 2 ja SHORT @@MoveIt ; at bol if BX - DX <= 2 ZERO si jmp SHORT @@Fin @@MoveIt: mov si, 1 ; move 1 character call backup_Cursor ; nb: decrements BX too @@Fin: ret ENDP mov_lchar ;---- mov_rchar ---------------------------------------------------------; ; Purpose: Moves cursor right in the commandline. ; ; Notes: none ; ; Entry: BX = pointer to current position in commandline, ; ; CH = # of bytes to end of line. ; ; Exit: BX++, ; ; CH--, ; ; SI = 1 (or 0 if already at eol). ; ; Calls: advance_Cursor ; ; Changes: SI, ; ; AX, BX, CH (advance_Cursor) ; ;--------------------------------------------------------------------------; PROC mov_rchar ZERO si ; set SI = 0 first or ch, ch jz SHORT @@Fin ; abort if CH = 0 inc si ; move 1 character call advance_Cursor ; nb: increments BX @@Fin: ret ENDP mov_rchar ;---- mov_lword ---------------------------------------------------------; ; Purpose: Moves cursor to start of previous word. ; ; Notes: none ; ; Entry: BX = pointer to current position in commandline, ; ; CH = # of bytes to end of line. ; ; Exit: BX and CH adjusted as appropriate. ; ; Calls: find_StartofPrevWord, backup_Cursor ; ; Changes: SI, (find_StartofPrevWord) ; ; AX, BX, CH (backup_Cursor) ; ;--------------------------------------------------------------------------; PROC mov_lword call find_StartofPrevWord call backup_Cursor ret ENDP mov_lword ;---- mov_rword ---------------------------------------------------------; ; Purpose: Moves cursor to start of next word. ; ; Notes: none ; ; Entry: BX = pointer to current position in commandline, ; ; CH = # of bytes to end of line. ; ; Exit: BX and CH adjusted as appropriate. ; ; Calls: find_StartofNextWord, advance_Cursor ; ; Changes: SI, (find_StartofNextWord) ; ; AX, BX, CH (advance_Cursor) ; ;--------------------------------------------------------------------------; PROC mov_rword call find_StartofNextWord call advance_Cursor ret ENDP mov_rword ;---- mov_bol -----------------------------------------------------------; ; Purpose: Moves cursor to start of commandline. ; ; Notes: none ; ; Entry: BX = pointer to current position in commandline, ; ; CH = # of bytes to end of line. ; ; Exit: BX = DX + 2, ; ; CH = # of characters in commandline, ; ; SI = # of characters backed up. ; ; Calls: backup_Cursor ; ; Changes: SI, ; ; AX, BX, CH (backup_Cursor) ; ;--------------------------------------------------------------------------; PROC mov_bol mov si, bx sub si, dx dec si dec si ; SI = BX - (DX + 2) call backup_Cursor ret ENDP mov_bol ;---- mov_eol -----------------------------------------------------------; ; Purpose: Moves cursor to end of commandline. ; ; Notes: none ; ; Entry: BX = pointer to current position in commandline, ; ; CH = # of bytes to end of line. ; ; Exit: BX += CH, ; ; CH = 0, ; ; SI = # of characters advanced. ; ; Calls: advance_Cursor ; ; Changes: SI, ; ; AX, BX, CH (advance_Cursor) ; ;--------------------------------------------------------------------------; PROC mov_eol mov al, ch ZERO ah mov si, ax ; SI = CH call advance_Cursor ret ENDP mov_eol ;---- mov_pcmd ----------------------------------------------------------; ; Purpose: Replaces current with previous commandline from buffer. ; ; Notes: none ; ; Entry: BX = pointer to current position in commandline, ; ; CH = # of bytes to end of line, ; ; CL = # of bytes left in commandline. ; ; Entry: BX = pointer to end of new commandline, ; ; CH = 0, ; ; CL = # of bytes left in new commandline, ; ; [CurCmd] adjusted. ; ; Calls: recall_CmdFromBuf, del_line ; ; Changes: CurCmd, ; ; AX, BX, CH, CL, SI, (recall_CmdFromBuf) ; ;--------------------------------------------------------------------------; PROC mov_pcmd push di ; Point DI to 2 bytes before CurCmd. Abort if this lies at or before ; start of recall buffer. mov di, [cs:CurCmd] dec di ; now at possible CR dec di ; now at possible cmd's last char cmp di, OFFSET RecallBuf jbe SHORT @@Abort ; Scan backwards to start of buffer or until finding another CR. push cx ; CH/CL for recall_CmdFromBuf pushf mov al, CR mov cx, di sub cx, OFFSET RecallBuf - 1 std ; scan backwards repne scasb ; uses ES:DI popf pop cx inc di ; should point to CR cmp [BYTE es:di], CR jne SHORT @@Abort ; Point SI to start of command and recall it. inc di mov si, di mov [cs:CurCmd], si call recall_CmdFromBuf jmp SHORT @@Fin ; Nothing to recall, so point CurCmd to start of buffer ; and delete current line. @@Abort: mov [cs:CurCmd], OFFSET RecallBuf call del_line @@Fin: pop di ret ENDP mov_pcmd ;---- mov_ncmd ----------------------------------------------------------; ; Purpose: Replaces current with next commandline from buffer. ; ; Notes: none ; ; Entry: BX = pointer to current position in commandline, ; ; CH = # of bytes to end of line, ; ; CL = # of bytes left in commandline. ; ; Entry: BX = pointer to end of new commandline, ; ; CH = 0, ; ; CL = # of bytes left in new commandline, ; ; [CurCmd] adjusted. ; ; Calls: recall_CmdFromBuf, del_line ; ; Changes: [CurCmd], ; ; AX, BX, CH, CL, SI (recall_CmdFromBuf) ; ;--------------------------------------------------------------------------; PROC mov_ncmd push di ; Point DI to CurCmd. Abort if this lies at or after LastByte. mov di, [cs:CurCmd] cmp di, OFFSET LastByte jae SHORT @@Abort ; Scan forwards to end of buffer or until finding another CR. ; NB: Scan stops before final CR in the recall buffer since ; there can never be a command after that; saves having to ; check DI against OFFSET LastByte. push cx ; CH/CL for recall_CmdFromBuf mov al, CR mov cx, OFFSET LastByte ; *not* OFFSET LastByte + 1 sub cx, di repne scasb ; uses ES:DI pop cx dec di ; should point to CR cmp [BYTE es:di], CR jne SHORT @@Abort ; Point SI to start of command and recall it. inc di ; point to 1st char in next cmd mov si, di mov [cs:CurCmd], si call recall_CmdFromBuf jmp SHORT @@Fin ; Nothing to recall, so point CurCmd to just past end ; of recall buffer and delete current line. @@Abort: mov [cs:CurCmd], OFFSET LastByte + 1 call del_line @@Fin: pop di ret ENDP mov_ncmd ;---- del_lchar ---------------------------------------------------------; ; Purpose: Deletes character to left of cursor. ; ; Notes: none ; ; Entry: BX = pointer to current position in commandline, ; ; CL = # of bytes left in commandline. ; ; Exit: BX--, ; ; CL++. ; ; Calls: mov_lchar, delete_Chars ; ; Changes: BX, (mov_lchar), ; ; AX, CH, CL, SI (delete_Chars) ; ;--------------------------------------------------------------------------; PROC del_lchar call mov_lchar ; sets SI = 0 (at bol) or 1 call delete_Chars ret ENDP del_lchar ;---- del_rchar ---------------------------------------------------------; ; Purpose: Deletes character at cursor. ; ; Notes: none ; ; Entry: BX = pointer to current position in commandline, ; ; CH = # of bytes to end of line, ; ; CL = # of bytes left in commandline. ; ; Exit: BX--, ; ; CH--, ; ; CL++. ; ; Calls: delete_Chars ; ; Changes: AX, CH, CL, SI (delete_Chars) ; ;--------------------------------------------------------------------------; PROC del_rchar or ch, ch jz SHORT @@Fin ; abort if already at eol mov si, 1 call delete_Chars @@Fin: ret ENDP del_rchar ;---- del_lword ---------------------------------------------------------; ; Purpose: Deletes word to left of cursor. ; ; Notes: none ; ; Entry: BX = pointer to current position in commandline, ; ; CH = # of bytes to end of line, ; ; CL = # of bytes left in commandline. ; ; Exit: BX, CH, and CL adjusted as appropriate. ; ; Calls: mov_lword, delete_Chars ; ; Changes: BX, (mov_lword), ; ; AX, CH, CL, SI (delete_Chars) ; ;--------------------------------------------------------------------------; PROC del_lword call mov_lword ; sets SI = 0 (at bol) or > 0 call delete_Chars ret ENDP del_lword ;---- del_rword ---------------------------------------------------------; ; Purpose: Deletes word to right of cursor. ; ; Notes: none ; ; Entry: BX = pointer to current position in commandline, ; ; CH = # of bytes to end of line, ; ; CL = # of bytes left in commandline. ; ; Exit: CH, and CL adjusted as appropriate. ; ; Calls: find_StartofNextWord, delete_Chars ; ; Changes: AX, CH, CL, SI (delete_Chars) ; ;--------------------------------------------------------------------------; PROC del_rword call find_StartofNextWord ; sets SI = 0 (at eol) or > 0 call delete_Chars ret ENDP del_rword ;---- del_bol -----------------------------------------------------------; ; Purpose: Deletes from cursor to start of commandline. ; ; Notes: none ; ; Entry: BX = pointer to current position in commandline, ; ; CH = # of bytes to end of line, ; ; CL = # of bytes left in commandline. ; ; Exit: BX = DX + 2, ; ; CH = number of characters in commandline, ; ; CL -= BX - DX - 2. ; ; Calls: mov_bol, delete_Chars ; ; Changes: BX, (mov_bol) ; ; AX, CH, CL, SI (delete_Chars) ; ;--------------------------------------------------------------------------; PROC del_bol call mov_bol ; sets SI = 0 (at bol) or > 0 call delete_Chars ret ENDP del_bol ;---- del_eol -----------------------------------------------------------; ; Purpose: Deletes from cursor to end of commandline. ; ; Notes: none ; ; Entry: BX = pointer to current position in commandline, ; ; CH = # of bytes to end of line, ; ; CL = # of bytes left in commandline. ; ; Exit: BX = DX + 2, ; ; CH = 0, ; ; CL -= CH. ; ; Calls: delete_Chars ; ; Changes: AX, CH, CL, SI (delete_Chars) ; ;--------------------------------------------------------------------------; PROC del_eol mov al, ch ZERO ah mov si, ax call delete_Chars ret ENDP del_eol ;---- del_line ----------------------------------------------------------; ; Purpose: Deletes entire commandline. ; ; Notes: none ; ; Entry: BX = pointer to current position in commandline, ; ; CH = # of bytes to end of line, ; ; CL = # of bytes left in commandline. ; ; Exit: BX = DX + 2, ; ; CH = 0, ; ; CL = [DX]. ; ; Calls: mov_bol, del_eol ; ; Changes: BX, (mov_bol) ; ; AX, CH, CL, SI (del_eol) ; ;--------------------------------------------------------------------------; PROC del_line call mov_bol call del_eol ret ENDP del_line ;---- del_buf -----------------------------------------------------------; ; Purpose: Deletes all commands in recall buffer. ; ; Notes: Does not affect current commandline. ; ; This function is not documented elsewhere. ; ; Entry: n/a ; ; Exit: [CurCmd] = OFFSET LastByte + 1. ; ; Calls: init_Buf ; ; Changes: AX, [CurCmd] (init_Buf) ; ;--------------------------------------------------------------------------; PROC del_buf mov [WORD cs:CurCmd], 0 call init_Buf ; nb: changes CurCmd ret ENDP del_buf ;---- toggle_InsMode ----------------------------------------------------; ; Purpose: Toggles flag for insert mode. ; ; Notes: none ; ; Entry: n/a ; ; Exit: [InsMode] toggled. ; ; Calls: none ; ; Changes: [InsMode] ; ;--------------------------------------------------------------------------; PROC toggle_InsMode xor [cs:InsMode], 1 ret ENDP toggle_InsMode ;---- init_Buf ----------------------------------------------------------; ; Purpose: Initializes recall buffer if necessary. ; ; Notes: Clears recall buffer if CurCmd is zero. Normally, CurCmd ; ; will take on values OFFSET RecallBuf and LastByte, ; ; or less. Zero should not otherwise occur. ; ; This is needed when scanning for previous commands - ; ; spurious CRs should not be encountered. ; ; Entry: [CurCmd] = pointer to current command in recall buffer. ; ; Exit: [CurCmd] = OFFSET LastByte + 1 if buffer is initialized. ; ; Calls: none ; ; Changes: AX, [CurCmd] possibly ; ;--------------------------------------------------------------------------; PROC init_Buf ; Abort if [CurCmd] is non-zero. cmp [WORD cs:CurCmd], 0 jne SHORT @@Fin ; Initialize buffer by zeroing out all but last byte. There put a CR ; so when searching backwards for commands I'll find at least one. push cx di ZERO al ; fill with zeros mov cx, BUFSIZE - 1 mov di, OFFSET RecallBuf rep stosb ; uses ES:DI mov [BYTE es:di], CR ; buffer ends with CR pop di cx ; Point current command to past end of recall buffer. This is so both ; mov_pcmd and mov_ncmd will not find any commands yet still function ; without error (which would happen if [CurCmd] were left at 0). mov [cs:CurCmd], OFFSET LastByte + 1 @@Fin: ret ENDP init_Buf ;---- get_CmdLine -------------------------------------------------------; ; Purpose: Reads a commandline from user. ; ; Notes: The caller's buffer is used as a scratch area to keep ; ; memory requirements to a minimum. ; ; Entry: DS:DX = buffer for storing commandline, ; ; [BYTE DS:DX] = maximum number of bytes to read. ; ; Exit: [BYTE DS:DX+1] = number of bytes actually read, ; ; [BYTE DS:DX+2] = 1st byte read from user. ; ; Calls: get_KeyNoEcho, add_CharToLine, [CmdTbl] ; ; Changes: AX, BX, CX, BP, [InsMode], [PrevCmd], [NextCmd] ; ;--------------------------------------------------------------------------; PROC get_CmdLine mov bx, dx ; BX used for indexed addressing ZERO ch ; bytes to end of line mov cl, [bx] ; space left in buffer dec cl ; less 1 for final CR inc bx ; pointer to first spot in buffer inc bx ; Get key and determine if it's an editing key or a regular character. @@NewKey: call get_KeyNoEcho ; get key from user cmp al, CR ; is user done yet? jz SHORT @@Fin cmp al, LF ; skip LF if stdin redirected jz SHORT @@NewKey cmp al, BS ; BS is an editing key je SHORT @@EditKey cmp al, ESCAPE ; ESCAPE is another je SHORT @@EditKey or al, al ; was key zero? jnz SHORT @@RegularChar ; no, then it's a regular char call get_KeyNoEcho ; yes, get extended scan code ; Process extended key as an editing key. Invalid keys are not added ; to the commandline buffer; instead, they merely result in a bell. @@EditKey: mov bp, OFFSET CmdTbl ; point to table of editing cmds @@NewCmd: cmp [(CMD PTR cs:bp).Key], al je SHORT @@ProcessCmd add bp, SIZE CmdTbl cmp [(CMD PTR cs:bp).Key], 0 ; zero marks end of table jne SHORT @@NewCmd ; and must point to ring_Bell ; so execution drops thru!!! @@ProcessCmd: call [(CMD PTR cs:bp).Function] jmp SHORT @@NewKey ; It's an ordinary character so add it to the commandline. @@RegularChar: call add_CharToLine jmp SHORT @@NewKey ; Now determine number of bytes in buffer, put that count in [DX+1], ; and terminate buffer with a CR. NB: count excludes final CR. @@Fin: mov bx, dx ; point back to start of buffer mov al, [bx] ; compute count sub al, cl dec al ; exclude final CR ZERO ah mov [bx+1], al ; [DS:DX+1] = count add bx, ax mov [BYTE bx+2], CR ; place CR at end of buffer ret ENDP get_CmdLine ;---- store_CmdInBuf ----------------------------------------------------; ; Purpose: Stores the commandline at the end of the recall buffer. ; ; Notes: Commandlines consisting of 1 character (CR) are not saved. ; ; Entry: DS:DX = pointer to start of commandline, ; ; [BYTE DS:DX+1] = maximum number of bytes to read. ; ; Exit: [CurCmd] = LastByte + 1. ; ; Calls: none ; ; Changes: AX, BX, CX, DI, SI, [CurCmd] ; ;--------------------------------------------------------------------------; PROC store_CmdInBuf ; Check length of commandline. mov bx, dx mov cl, [bx+1] or cl, cl ; CL does not include final CR jz SHORT @@Fin ; so if = 0, nothing's there inc cl ; else set CX = # bytes in cmd ZERO ch ; *including* final CR ; Make room in recall buffer for commandline by shifting everything ; back by [DS:DX+1] characters. push cx ds ; need both to copy to recall buf mov ax, cs mov ds, ax mov di, OFFSET RecallBuf ; to start of buffer mov si, di add si, cx ; from start + CX neg cx add cx, BUFSIZE ; for BUFSIZE - [BYTE BX+1] rep movsb ; move them pop ds cx ; Add commandline in empty space at end of recall buffer. By this ; point DI will point to space for current commandline. mov si, bx inc si inc si rep movsb ; from DS:SI to ES:DI mov [cs:CurCmd], OFFSET LastByte + 1 @@Fin: ret ENDP store_CmdInBuf ;---- do_Int21 ----------------------------------------------------------; ; Purpose: Passes calls to input strings along to my own handler. ; ; Notes: none ; ; Entry: AH = subfunction to perform ; ; Exit: If AH = 10, DS:DX points to buffer read from user. ; ; Calls: init_Buf, get_CmdLine, store_CmdInBuf ; ; Changes: flags ; ;--------------------------------------------------------------------------; PROC do_Int21 FAR ; This structure is used to share intrrupts. The real entry point ; follows immediately after it. my_Int21 ISR < , , , 0, ((@@hw_reset - $ - 2) SHL 8 + 0ebh), > ; If the call is for buffered input, then use my handler; ; otherwise, pass it along to the old handler. cmp ah, 10 jz SHORT @@SwitchStack jmp [cs:my_Int21.OldISR] ; no, pass it along ; nb: old vector issues IRET ; Switch over to my own stack and save callers registers. @@SwitchStack: mov [cs:OldAX], ax ; can't push it on my stack yet cli ; critical part - disallow INTs mov [WORD cs:OldStack], sp mov [WORD cs:OldStack+2], ss mov ax, cs mov ss, ax mov sp, OFFSET StackTop sti ; ok, out of critical section push bx cx dx di si bp ds es ; Meat of my interrupt handler. mov es, ax ; set ES = CX cld call init_Buf call get_CmdLine call store_CmdInBuf ; Restore caller's registers. pop es ds bp si di dx cx bx cli mov ss, [WORD cs:OldStack+2] mov sp, [WORD cs:OldStack] sti mov ax, [cs:OldAX] iret ; return to caller ; Required for IBM Interrupt Sharing Protocol. Normally it is used ; only by hardware interrupt handlers. @@hw_reset: retf ENDP do_Int21 ;---- do_Int2D ----------------------------------------------------------; ; Purpose: Handle INT 2D. ; ; Notes: Only the install check is truly supported. ; ; Entry: AH = Multiplex ID, ; ; AL = function code ; ; Exit: AL = FF in the case of an install check, ; ; CX = TSR version, ; ; DX:DI points to resident copy of TSR signature. ; ; Calls: n/a ; ; Changes: AL, CX, DX, DI ; ;--------------------------------------------------------------------------; PROC do_Int2D FAR ; This structure is used to share intrrupts. The real entry point ; follows immediately after it. my_Int2D ISR < , , , 0, ((@@hw_reset - $ - 2) SHL 8 + 0ebh), > ; Test if request is for me. Pass it along to next ISR in chain if not. cmp ah, [cs:MPlex] ; my multiplex ID? jz SHORT @@forMe ; yes jmp [cs:my_Int2d.OldISR] ; no, pass it along ; nb: old vector issues IRET ; Check function as specified in AL. @@forMe: cmp al, 0 ; installation check jz SHORT @@InstallCheck cmp al, 1 ; get entry point jz SHORT @@GetEntryPoint cmp al, 2 ; uninstall jz SHORT @@Uninstall ZERO al ; mark as not implemented jmp SHORT @@Fin @@InstallCheck: dec al ; set AL = FF mov cx, [cs:TSR_Ver] ; CH = major; CL = minor mov dx, cs ; DX:DI points to sig string mov di, OFFSET TSR_Sig jmp SHORT @@Fin @@GetEntryPoint: ZERO al ; mark as not supported jmp SHORT @@Fin @@Uninstall: ZERO al ; not implemented in API jmp SHORT @@Fin @@Fin: iret ; return to caller ; Required for IBM Interrupt Sharing Protocol. Normally it is used ; only by hardware interrupt handlers. @@hw_reset: retf ENDP do_Int2D %NEWPAGE ;--------------------------------------------------------------------------; ; R E C A L L B U F F E R ; ;--------------------------------------------------------------------------; RecallBuf = $ ; will overlay transient portion LastByte = RecallBuf + BUFSIZE - 1 ; room for BUFSIZE characters ; and end of resident portion %NEWPAGE ;--------------------------------------------------------------------------; ; T R A N S I E N T D A T A ; ;--------------------------------------------------------------------------; ProgName DB 'recall: ' DB EOS EOL DB '.', CR, LF DB EOS HelpMsg DB CR, LF DB 'TifaWARE RECALL, v', VERSION, ', ', ??Date DB ' - commandline editor and history TSR.', CR, LF DB 'Usage: recall [-options]', CR, LF, LF DB 'Options:', CR, LF DB ' -i = install in memory', CR, LF DB ' -l = list commandlines in recall buffer', CR, LF DB ' -r = remove from memory', CR, LF DB ' -? = display this help message', CR, LF, LF DB 'Only one option can be specified at a time.' DB CR, LF, EOS ErrMsgOpt DB 'illegal option -- ' OptCh DB ? ; room for offending character DB EOS ErrMsgVer DB 'DOS v1 is not supported' DB EOS ErrMsgRes DB 'unable to go resident' DB EOS ErrMsgRem DB 'unable to remove from memory' DB EOS ErrMsgNYI DB 'not yet installed' DB EOS InstalMsg DB 'TifaWARE RECALL, v', VERSION DB ' now installed.' DB CR, LF, EOS RemoveMsg DB 'successfully removed' DB EOS SwitCh DB '-' ; char introducing options HFlag DB 0 ; flag for on-line help IFlag DB 0 ; flag for installing TSR LFlag DB 0 ; flag for listing commandlines RFlag DB 0 ; flag for removing TSR %NEWPAGE ;--------------------------------------------------------------------------; ; T R A N S I E N T C O D E ; ;--------------------------------------------------------------------------; ;---- go_Resident -------------------------------------------------------; ; Purpose: Attempts to make TSR resident. ; ; Notes: Aborts if there's not enough memory to satisfy request. ; ; This procedure ONLY EXITS ON ERROR. ; ; Entry: DS = segment address of program's PSP, which also holds ; ; HookTbl, a structure of type ISRHOOK. ; ; Exit: none ; ; Calls: check_ifInstalled, fputs, fake_Env, install_TSR, errmsg ; ; Changes: AX, BX, CX, DX, DI, SI, ES ; ;--------------------------------------------------------------------------; PROC go_Resident ; See if there's already a copy resident. nb: only interested in AX ; on return from the install check. mov si, OFFSET TSR_SIG call check_ifInstalled ; -> AX, CX, and DX:DI cmp al, 2 ; out of multiplex ids? jz SHORT @@Abort ; yes, abort cmp al, 1 ; already loaded? jz SHORT @@Abort ; yes mov [MPlex], ah ; save mplex id ; This is the point of no-return -- if we get here we're going resident. mov bx, STDOUT mov dx, OFFSET InstalMsg call fputs ; Create a fake environment and free existing one. ; Make sure that ES points to PSP. ZERO cx ; tells fake_Env to fake it push ds pop es call fake_Env ; Ok, all that's left is to go resident. ; **************************************************************************** ; NB: TASM's IDEAL mode treats arguments of the OFFSET operator in a peculiar ; fashion, as can be seen by browsing the lexical grammer in Appendix A of ; the _Reference Guide_. If MASM mode were used, the expression below would ; be written "(OFFSET LastByte - OFFSET SegStart + 16) SHR 5". However, in ; IDEAL mode not only would "OFFSET SegStart + 16" be parsed as "OFFSET ; (SegStart + 16)" but also the result would be viewed as a relative quantity. ; As it is, TASM replaces labels below with their respective address values ; thereby computing the "correct" amount of memory to save. ; **************************************************************************** ; NB: While Angermayer and Jaeger in their book say 15 should be used ; below, I've found 16 is necessary to handle cases in which LastByte ; lies at the start of a paragraph. So what if I'm wasting an entire ; paragraph! ; **************************************************************************** mov dx, (LastByte - SegStart + 16) SHR 4 mov bx, OFFSET HookTbl ; pointer to ISRHOOK structure call install_TSR ; never returns ; Execution gets here only on error because: ; - all multiplex ids are in use! ; - the TSR is already resident. @@Abort: mov dx, OFFSET ErrMsgRes ; "unable to go resident" call errmsg ret ENDP go_Resident ;---- clear_Resident ----------------------------------------------------; ; Purpose: Attempts to remove a TSR from memory. ; ; Notes: none ; ; Entry: DS = segment address of program's PSP. ; ; Exit: AL = 0 if removal succeeded; ERRNYI if not installed; ; ; ERRUNI otherwise. ; ; Calls: check_ifInstalled, remove_TSR, errmsg ; ; Changes: AX, BX, CX, DX, DI, SI, ES ; ;--------------------------------------------------------------------------; PROC clear_Resident ; See if there's already a copy resident. mov si, OFFSET TSR_SIG call check_ifInstalled ; DS:SI -> AX, CX, DX:DI cmp al, 1 ; already loaded? jz SHORT @@Removal ; yes mov al, ERRNYI ; no, set return code mov dx, OFFSET ErrMsgNYI ; "not yet installed" jmp SHORT @@Fin ; Try to remove it. @@Removal: mov bx, OFFSET HookTbl ; HookTbl in resident data area mov es, dx ; install check returns DX:DI call remove_TSR ; ES:BX -> n/a jc SHORT @@Abort ZERO al mov dx, OFFSET RemoveMsg jmp SHORT @@Fin @@Abort: mov al, ERRUNI mov dx, OFFSET ErrMsgRem ; "unable to remove" @@Fin: call errmsg ret ENDP clear_Resident ;---- list_CmdLines -----------------------------------------------------; ; Purpose: Lists commandlines in recall buffer. ; ; Notes: none ; ; Entry: none ; ; Exit: AL = 0 if successful; ERRNYI otherwise. ; ; Calls: check_ifInstalled, errmsg ; ; Changes: AX, CX, DX, DI, SI, ES ; ;--------------------------------------------------------------------------; PROC list_CmdLines mov si, OFFSET TSR_SIG call check_ifInstalled ; DS:SI -> AX, CX, DX:DI cmp al, 1 ; already loaded? jnz SHORT @@Abort ; no push ds mov ds, dx ; point DS into resident data mov es, dx ; ES too ; Point to start of 1st complete command in recall buffer. NB: ; there will always be at least one command - "recall -l". mov al, CR mov cx, BUFSIZE mov di, OFFSET RecallBuf repne scasb ; uses ES:DI ; Display rest of buffer. NB: This is done character one character at ; a time because buffered lines end with CR, not 0. mov ah, 2 ; DOS subfunction to display char @@NextChar: mov dl, [di] ; get char inc di int DOS ; display it cmp dl, CR ; need to display CR/LF? loopne SHORT @@NextChar ; always decrements CX mov dl, LF ; display LF now int DOS or cx, cx ; done yet? jnz SHORT @@NextChar pop ds ZERO al ; flag no error jmp SHORT @@Fin @@Abort: mov dx, OFFSET ErrMsgNYI call errmsg mov al, ERRNYI @@Fin: ret ENDP list_CmdLines ;---- skip_Spaces -------------------------------------------------------; ; Purpose: Skips past spaces in a string. ; ; Notes: Scanning stops with either a non-space *OR* CX = 0. ; ; Entry: DS:SI = start of string to scan. ; ; Exit: AL = next non-space character, ; ; CX is adjusted as necessary, ; ; DS:SI = pointer to next non-space. ; ; Calls: none ; ; Changes: AL, CX, SI ; ;--------------------------------------------------------------------------; PROC skip_Spaces jcxz SHORT @@Fin @@NextCh: lodsb cmp al, ' ' loopz @@NextCh jz SHORT @@Fin ; CX = 0; don't adjust inc cx ; adjust counters if cx > 0 dec si @@Fin: ret ENDP skip_Spaces ;---- get_Opt -----------------------------------------------------------; ; Purpose: Get a commandline option. ; ; Notes: none ; ; Entry: AL = option character, ; ; Exit: n/a ; ; Calls: tolower, errmsg ; ; Changes: AX, DX, [OptCh], [HFlag], [IFlag], [LFlag], [RFlag] ; ;--------------------------------------------------------------------------; PROC get_Opt mov [OptCh], al ; save for later call tolower ; use only lowercase in cmp. cmp al, 'i' jz SHORT @@OptI cmp al, 'l' jz SHORT @@OptL cmp al, 'r' jz SHORT @@OptR cmp al, '?' jz SHORT @@OptH mov dx, OFFSET ErrMsgOpt ; unrecognized option call errmsg ; then *** DROP THRU *** to OptH ; Various possible options. @@OptH: mov [HFlag], ON ; set help flag jmp SHORT @@Fin @@OptI: mov [IFlag], ON ; install in memory jmp SHORT @@Fin @@OptL: mov [LFlag], ON ; list cmds in recall buffer jmp SHORT @@Fin @@OptR: mov [RFlag], ON ; remove from memory @@Fin: ret ENDP get_Opt ;---- process_CmdLine ---------------------------------------------------; ; Purpose: Processes commandline arguments. ; ; Notes: A switch character by itself is ignored. ; ; Entry: n/a ; ; Exit: n/a ; ; Calls: skip_Spaces, get_Opt ; ; Changes: AX, CX, SI, ; ; DX, [OptCh], [HFlag], [IFlag], [LFlag], [RFlag] (get_Opt) ; ; Direction flag is cleared. ; ;--------------------------------------------------------------------------; PROC process_CmdLine cld ; forward, march! ZERO ch mov cl, [CmdLen] ; length of commandline mov si, OFFSET CmdLine ; offset to start of commandline call skip_Spaces ; check if any args supplied or cl, cl jnz SHORT @@ArgLoop mov [HFlag], ON ; assume user needs help jmp SHORT @@Fin ; For each blank-delineated argument on the commandline... @@ArgLoop: lodsb ; next character dec cl cmp al, [SwitCh] ; is it the switch character? jnz SHORT @@NonOpt ; no ; Isolate each option and process it. Stop when a space is reached. @@OptLoop: jcxz SHORT @@Fin ; abort if nothing left lodsb dec cl cmp al, ' ' jz SHORT @@NextArg ; abort when space reached call get_Opt jmp @@OptLoop ; Any argument which is *not* an option is invalid. Set help flag and abort. @@NonOpt: mov [HFlag], ON jmp SHORT @@Fin ; Skip over spaces until next argument is reached. @@NextArg: call skip_Spaces or cl, cl jnz @@ArgLoop @@Fin: ret ENDP process_CmdLine ;---- main --------------------------------------------------------------; ; Purpose: Main section of program. ; ; Notes: none ; ; Entry: Arguments as desired ; ; Exit: Return code as follows: ; ; 0 => program ran successfully, ; ; ERRH => on-line help supplied, ; ; ERRINS => program could not be installed, ; ; ERRNYI => program was not yet installed. ; ; Calls: process_CmdLine, fputs, list_CmdLines, install_TSR, ; ; uninstall_TSR ; ; Changes: n/a ; ;--------------------------------------------------------------------------; main: ; Must be running at least DOS v2.x. call getvdos cmp al, 2 jae SHORT @@ReadCmds mov dx, OFFSET ErrMsgVer ; gotta have at least DOS v2 call errmsg ; Parse commandline. @@ReadCmds: call process_CmdLine ; process commandline args cmp [IFlag], ON ; install it? je SHORT @@Install cmp [LFlag], ON ; list commands? je SHORT @@List cmp [RFlag], ON ; remove it? je SHORT @@Remove mov bx, STDERR ; user must need help mov dx, OFFSET HelpMsg call fputs mov al, ERRH jmp SHORT @@Fin @@List: call list_CmdLines jmp SHORT @@Fin @@Install: call go_Resident ; returns on error only mov al, ERRINS jmp SHORT @@Fin @@Remove: call clear_Resident ; Terminate the program using as return code what's in AL. @@Fin: mov ah, 4ch int DOS EVEN ;-------------------------------------------------------------------------; ; Purpose: Writes an ASCIIZ string to specified device. ; Notes: A zero-length string doesn't seem to cause problems when ; this output function is used. ; Requires: 8086-class CPU and DOS v2.0 or better. ; Entry: BX = device handle, ; DS:DX = pointer to string. ; Exit: Carry flag set if EOS wasn't found or handle is invalid. ; Calls: strlen ; Changes: none ;-------------------------------------------------------------------------; PROC fputs push ax cx di es mov ax, ds mov es, ax mov di, dx call strlen ; set CX = length of string jc SHORT @@Fin ; abort if problem finding end mov ah, 40h ; MS-DOS raw output function int DOS @@Fin: pop es di cx ax ret ENDP fputs EVEN ;-------------------------------------------------------------------------; ; Purpose: Writes an error message to stderr. ; Notes: none ; Requires: 8086-class CPU and DOS v2.0 or better. ; Entry: DS:DX = pointer to error message. ; Exit: n/a ; Calls: fputs ; Changes: none ;-------------------------------------------------------------------------; PROC errmsg push bx dx mov bx, STDERR mov dx, OFFSET ProgName ; display program name call fputs pop dx ; recover calling parameters push dx ; and save again to avoid change call fputs ; display error message mov dx, OFFSET EOL call fputs pop dx bx ret ENDP errmsg EVEN ;-------------------------------------------------------------------------; ; Purpose: Gets version of DOS currently running. ; Notes: none ; Requires: 8086-class CPU and DOS v2.0 or better. ; Entry: n/a ; Exit: AL = major version number, ; AH = minor version number (2.1 = 10). ; Calls: none ; Changes: AX ;-------------------------------------------------------------------------; PROC getvdos push bx cx ; DOS destroys bx and cx! mov ah, 30h int DOS pop cx bx ret ENDP getvdos EVEN ;--------------------------------------------------------------------------; ; Purpose: Gets address of an interrupt handler. ; Notes: none ; Requires: 8086-class CPU and DOS v2.0 or better. ; Entry: AL = interrupt of interest. ; Exit: ES:BX = address of current interrupt handler ; Calls: none ; Changes: ES:BX ;--------------------------------------------------------------------------; PROC getvect push ax mov ah, 35h ; find address of handler int DOS ; returned in ES:BX pop ax ret ENDP getvect ;--------------------------------------------------------------------------; ; Purpose: Sets an interrupt vector. ; Notes: none ; Requires: 8086-class CPU and DOS v1.0 or better. ; Entry: AL = interrupt of interest, ; DS:DX = address of new interrupt handler ; Exit: n/a ; Calls: none ; Changes: none ;--------------------------------------------------------------------------; PROC setvect push ax mov ah, 25h ; set address of handler int DOS pop ax ret ENDP setvect EVEN ;--------------------------------------------------------------------------; ; Purpose: Finds the next in a chain of ISRs. ; Notes: ISRs must be shared according to the IBM Interrupt ; Sharing Protocol. ; Requires: 8086-class CPU. ; Entry: ES:BX = entry point for a given ISR. ; Exit: ES:BX = entry point for next ISR in the chain, ; cf = 1 on error ; Calls: none ; Changes: BX, ES, cf ;--------------------------------------------------------------------------; PROC find_NextISR ; Save DS, then set it to ES. This will avoid segment overrides below. push ds es pop ds ; Run three tests to see if the ISR obeys the protocol. ;1) Entry should be a short jump (opcode 0EBh). ;2) Sig should equal a special value ("KB"). ;3) Reset should be another short jump. cmp [BYTE PTR (ISR PTR bx).Entry], 0ebh jnz SHORT @@Abort cmp [(ISR PTR bx).Sig], TSRMAGIC jnz SHORT @@Abort cmp [BYTE PTR (ISR PTR bx).Reset], 0ebh jnz SHORT @@Abort ; Ok, looks like the ISR is following the Interrupt Sharing Protocol. ; nb: cf will be clear as a result of the last comparison. les bx, [(ISR PTR bx).OldISR] jmp SHORT @@Fin ; Uh, oh, somebody's not being very cooperative or we've hit DOS/BIOS. @@Abort: stc ; flag error @@Fin: pop ds ret ENDP find_NextISR ;--------------------------------------------------------------------------; ; Purpose: Finds the previous in a chain of ISRs. ; Notes: ISRs must be shared according to the IBM Interrupt ; Sharing Protocol. ; Requires: 8086-class CPU and DOS v2.0 or better. ; Entry: AL = vector hooked, ; ES:BX = entry point for a given ISR. ; Exit: ES:BX = entry point for next ISR in the chain, ; cf = 1 on error ; Calls: getvect, find_NextISR ; Changes: BX, ES, cf ;--------------------------------------------------------------------------; PROC find_PrevISR push ax cx dx ; Stack holds previous ISR. Initialize it to a null pointer. ZERO cx push cx cx ; Point CX:DX to current ISR, then get first ISR in the chain. mov cx, es mov dx, bx call getvect ; AL -> ES:BX jmp SHORT @@Cmp ; Cycle through ISRs until either a match is found or we can't go further. @@Next: add sp, 4 ; get rid of two words on stack push es bx ; now save ES:BX call find_NextISR ; ES:BX -> ES:BX jc SHORT @@Fin ; abort on error @@Cmp: mov ax, es ; are segs the same? cmp ax, cx jnz SHORT @@Next cmp dx, bx ; what about offsets? jnz SHORT @@Next @@Fin: pop bx es ; pointer to previous ISR pop dx cx ax ret ENDP find_PrevISR ;--------------------------------------------------------------------------; ; Purpose: Hooks into an ISR and keeps track of previous ISR. ; Notes: none ; Requires: 8086-class CPU and DOS v2.0 or better. ; Entry: AL = vector to hook, ; ES:BX = pointer to a structure of type ISR. ; Exit: n/a ; Calls: getvect, setvect ; Changes: n/a ;--------------------------------------------------------------------------; PROC hook_ISR push bx dx bp ds es ; Save old vector to it can be restored later. Then set new hook. push es bx ; need them later call getvect ; AL -> ES:BX pop dx ds ; recover pointer to ISR mov bp, dx ; use BP for indexing mov [WORD (ISR PTR bp).OldISR], bx mov [WORD ((ISR PTR bp).OldISR)+2], es call setvect ; uses DS:DX pop es ds bp dx bx ret ENDP hook_ISR ;--------------------------------------------------------------------------; ; Purpose: Unhooks an ISR if possible. ; Notes: Unhooking an ISR is more complicated than hooking one ; because of the need to support interrupt sharing. ; Requires: 8086-class CPU and DOS v2.0 or better. ; Entry: AL = vector hooked, ; ES:BX = entry point of current ISR. ; Exit: cf = 1 on error ; Calls: find_PrevISR, setvect ; Changes: cf ;--------------------------------------------------------------------------; PROC unhook_ISR push bx cx dx ds es ; Point DS:DX to next ISR, then ES:BX to previous ISR in the chain. lds dx, [(ISR PTR es:bx).OldISR] call find_PrevISR ; ES:BX -> ES:BX jc SHORT @@Fin ; abort on error ; If find_PrevISR() returned a null pointer, then the current ISR ; is first in the chain; just use DOS to reassign the vector. ; Otherwise, update the OldISR entry in the previous handler. mov cx, es ; did find_PrevISR() ... or cx, bx ; return null pointer? jnz SHORT @@Update ; no. update OldISR call setvect ; yes, hook AL to DS:DX jmp SHORT @@Fin @@Update: mov [WORD (ISR PTR es:bx).OldISR], dx mov [WORD ((ISR PTR es:bx).OldISR)+2], ds @@Fin: pop es ds dx cx bx ret ENDP unhook_ISR EVEN AMI equ 2dh ; Alternate Multiplex Interrupt ENVBLK equ 2ch ; ptr in PSP to environment block ;--------------------------------------------------------------------------; ; Purpose: Frees up a program's environment block. ; Notes: Programs such as PMAP or MEM scan environment blocks to ; learn names of TSRs. Freeing it means such programs ; will not be able to identify the TSR. ; It's ASSUMED the ENV BLOCK has NOT ALREADY been FREED. ; Requires: 8086-class CPU and DOS v2.0 or better. ; Entry: ES = segment of program's PSP. ; Exit: none ; Calls: none ; Changes: none ;--------------------------------------------------------------------------; PROC free_Env push ax ds es push es ; point DS to PSP too pop ds mov es, [ENVBLK] ; pointer to env block mov ah, 49h ; free memory block int DOS mov [WORD PTR ENVBLK], 0 ; make it 0 pop es ds ax ret ENDP free_Env ;--------------------------------------------------------------------------; ; Purpose: Replaces a program's real environment with a smaller, fake ; one to save space. Programs like PMAP and MEM though ; will still be able to identify TSRs. ; Notes: If run with DOS version lower than v3.10, the environment ; block is merely freed. ; Requires: 8086-class CPU and DOS v2.0 or better. ; Entry: CX = size in bytes of pseudo-environment block (if 0 ; one is created containing just program name/args), ; DS:SI = pointer to pseudo-environment block, ; ES = segment of program's PSP. ; Exit: none ; Calls: getvdos, free_Env, strlen ; Changes: none ;--------------------------------------------------------------------------; PROC fake_Env push ax bx cx di si ds es pushf ; Make sure DOS is v3.10 or better. If not, just free environment. ; nb: I could code this to handle old versions so long as caller ; supplies a real block, but why bother? call getvdos ; get DOS version xchg al, ah cmp ax, (3 SHL 8) + 10 ; v3.10 or better? jae SHORT @@FindEnv ; yes call free_Env ; no, just free it jmp SHORT @@Fin ; Locate environment block. @@FindEnv: mov bx, [es:ENVBLK] ; pointer to env block mov es, bx ; If CX is zero, point DS:SI to just the program name/args in the ; current environment. This format was introducted with DOS v3.10. ; ; nb: Refer to _Undocumented DOS, p 399 for format of environment block. cld ; scasb and movsb must go forward or cx, cx ; is CX zero? jnz SHORT @@GetMem ; no mov ds, bx ; point DS to env block too ZERO al ; ends of ASCIIz strings ZERO di ; start at offset 0 @@NextString: call strlen ; find length of string at ES:DI add di, cx ; update DI inc di ; and past EOS scasb ; are we at another 0? jne SHORT @@NextString ; no mov si, di ; point SI to dec si ; EOS in ... dec si ; last string mov [WORD PTR es:di], 1 ; only want prog name/args inc di ; point to start of string inc di call strlen ; find its length add cx, di ; get # bytes to move sub cx, si inc cx ; At this point, CX holds number of bytes to allocate and DS:SI point ; to a copy of the pseudo-environment block. @@GetMem: ZERO di ; either way, destination = 0 mov bx, cx ; from # bytes REPT 4 shr bx, 1 ; get # paragraphs ENDM inc bx ; think what if CX < 0fh push bx ; must save BX if DOS fails mov ah, 48h ; allocate memory int DOS ; returns block in AX pop bx jc SHORT @@JustResize ; cf => failure ; Memory allocation succeeded so: (1) Copy to new block. (2) Adjust ; pointer in program's PSP. (3) Free old block. push es ; points to old env block mov es, ax ; new block rep movsb mov ah, 62h ; get program's PSP int DOS ; returns it in BX mov ds, bx mov [ENVBLK], es ; pointer to new env block pop es ; recover pointer to old env mov ah, 49h ; free it int DOS jmp SHORT @@Fin ; Memory allocation failed so we'll use existing block and resize it. @@JustResize: rep movsb mov ah, 4ah ; modify allocation int DOS @@Fin: popf pop es ds si di cx bx ax ret ENDP fake_Env ;--------------------------------------------------------------------------; ; Purpose: Checks if a TSR has been installed in memory. ; Notes: For a description of the steps followed here, see Ralf ; Brown's alternate multiplex proposal. ; This procedure MUST BE RUN before going resident and ; the multiplex id returned SHOULD BE SAVED in the ; resident data area. ; Requires: 8086-class CPU ; Entry: DS:SI = pointer to TSR's signature string. ; Exit: AL = 0 if not installed, = 1 if installed, = 2 if all ; multiplex ids are in use, ; AH = multiplex id to use based on AL, ; CX = TSR version number if installed, ; DX:DI = pointer to resident copy of TSR's sig if AL = 1. ; Calls: getvect, memcmp ; Changes: AX, CX, DX, DI ;--------------------------------------------------------------------------; PROC check_ifInstalled push bx es ; Do a quick check to see if 2d is hooked. mov al, AMI ; alternate multiplex interrupt call getvect ; handler address in ES:BX ZERO ax cmp [BYTE PTR es:bx], 0cfh ; is it IRET opcode? jz SHORT @@Fin ; yes, return with AX = 0 ; Do an install check on each possible multiplex id. ZERO bx ; marks 1st unused mplex id @@CheckIt: ZERO al ; be sure to do install check int AMI ; might trash CX and DX:DI or al, al ; is AL zero still? jnz SHORT @@CmpSigs ; no, multiplex's in use ; It's not in use. Save if it's the first. or bl, bl ; 1st available id found already? jnz SHORT @@NextMPlex ; yes inc bl ; no, but flag it now mov bh, ah ; and hold onto mplex jmp SHORT @@NextMPlex ; Compare first 16 bytes of sigs. DS:SI points to a known sig; ; DX:DI to one somewhere in resident code. @@CmpSigs: push cx ; save TSR version number mov cx, 16 ; # bytes in sigs to compare mov es, dx ; memcmp() needs ES:DI and DS:SI call memcmp pop cx ; recover TSR version number jnz SHORT @@NextMPlex mov al, 1 jmp SHORT @@Fin ; Move on to next multiplex number. @@NextMPlex: add ah, 1 ; sets zf if AH was 255. Done? jnz SHORT @@CheckIt ; no, back for more mov ah, bh ; yes, AH = 1st available id or dl, bl ; did we run out? jnz SHORT @@Fin ; no mov al, 2 ; yes @@Fin: pop es bx ret ENDP check_ifInstalled ;--------------------------------------------------------------------------; ; Purpose: Installs a TSR in memory. ; Notes: This procedure never returns. ; No changes are made here to the environment block. ; Entry points are assumed relative to ES. ; Call check_ifInstalled() to determine which multiplex ; id will be used. ; Requires: 8086-class CPU and DOS v2.0 or better. ; Entry: DX = number of paragraphs to reserve, ; ES:BX = pointer to a structure of ISRHOOK. ; Exit: n/a ; Calls: hook_ISR ; Changes: n/a ;--------------------------------------------------------------------------; PROC install_TSR ; Set hooks as specified by ISRHOOK structure. mov bp, bx ; BX needed when hooking ISRs @@NextHook: mov al, [(ISRHOOK PTR bp).Vector] mov bx, [(ISRHOOK PTR bp).Entry] call hook_ISR ; AL, ES:BX -> n/a add bp, SIZE ISRHOOK cmp al, AMI ; at end of table? jnz SHORT @@NextHook ; no ; And now go resident. Note that DX already holds # paragraphs to keep. mov ax, 3100h ; terminate/stay resident, rc = 0 int DOS ; via DOS ret ; ***never reached*** ENDP install_TSR ;--------------------------------------------------------------------------; ; Purpose: Removes a TSR if possible. ; Notes: Caller should use check_ifInstalled() to make sure the ; TSR has first been installed. ; Entry points are assumed to be relative to ES. ; Requires: 8086-class CPU and DOS v2.0 or better. ; Entry: ES:BX = pointer to a structure of ISRHOOK. ; Exit: cf set if operation failed ; Calls: find_PrevISR, unhook_ISR ; Changes: AX, cf ;--------------------------------------------------------------------------; PROC remove_TSR push bx dx bp ds es ; save registers ; Set DS to ES to avoid segment overrides. Also, use BP for indexing into ; the hook table, and save it in DX as it's needed later. push es pop ds mov bp, bx mov dx, bx ; For each vector in the hook table, make sure the ISR can be unhooked. @@NextVect: mov al, [(ISRHOOK PTR bp).Vector] mov bx, [(ISRHOOK PTR bp).Entry] push es ; hang onto this call find_PrevISR ; able to find it? pop es jc SHORT @@Fin ; no, abort add bp, SIZE ISRHOOK cmp al, AMI ; at end of table? jnz SHORT @@NextVect ; no ; It's possible to unhook all vectors, so go to it. mov bp, dx @@NextHook: mov al, [(ISRHOOK PTR bp).Vector] mov bx, [(ISRHOOK PTR bp).Entry] call unhook_ISR ; AL, ES:BX -> n/a jc SHORT @@Fin ; it had better succeed! add bp, SIZE ISRHOOK cmp al, AMI ; at end of table? jnz SHORT @@NextHook ; no ; Now free TSR's memory. mov bx, [ENVBLK] or bx, bx ; any environment block? jz SHORT @@MainMem ; no mov es, bx ; yes, free it mov ah, 49h int DOS ; trashes AH jc SHORT @@Fin ; shouldn't be necessary @@MainMem: mov ah, 49h mov bx, ds ; free TSR's memory mov es, bx int DOS @@Fin: pop es ds bp dx bx ; pop registers ret ENDP remove_TSR EVEN ;-------------------------------------------------------------------------; ; Purpose: Converts character to lowercase. ; Notes: none ; Requires: 8086-class CPU. ; Entry: AL = character to be converted. ; Exit: AL = converted character. ; Calls: none ; Changes: AL ; flags ;-------------------------------------------------------------------------; PROC tolower cmp al, 'A' ; if < 'A' then done jb SHORT @@Fin cmp al, 'Z' ; if > 'Z' then done ja SHORT @@Fin or al, 20h ; make it lowercase @@Fin: ret ENDP tolower ;-------------------------------------------------------------------------; ; Purpose: Converts character to uppercase. ; Notes: none ; Requires: 8086-class CPU. ; Entry: AL = character to be converted. ; Exit: AL = converted character. ; Calls: none ; Changes: AL ; flags ;-------------------------------------------------------------------------; PROC toupper cmp al, 'a' ; if < 'a' then done jb SHORT @@Fin cmp al, 'z' ; if > 'z' then done ja SHORT @@Fin and al, not 20h ; make it lowercase @@Fin: ret ENDP toupper EVEN ;--------------------------------------------------------------------------; ; Purpose: Compares two regions of memory. ; Notes: none ; Requires: 8086-class CPU. ; Entry: CX = number of bytes to compare, ; DS:SI = start of 1st region of memory, ; ES:DI = start of 2nd region. ; Exit: zf = 1 if equal. ; Calls: none ; Changes: zf ;--------------------------------------------------------------------------; PROC memcmp push cx di si pushf ; save direction flag cld repe cmpsb ; compare both areas popf ; recover direction flag dec di dec si cmpsb ; set flags based on final byte pop si di cx ret ENDP memcmp EVEN ;-------------------------------------------------------------------------; ; Purpose: Calculates length of an ASCIIZ string. ; Notes: Terminal char is _not_ included in the count. ; Requires: 8086-class CPU. ; Entry: ES:DI = pointer to string. ; Exit: CX = length of string, ; cf = 0 and zf = 1 if EOS found, ; cf = 1 and zf = 0 if EOS not found within segment. ; Calls: none ; Changes: CX, ; flags ;-------------------------------------------------------------------------; PROC strlen push ax di pushf cld ; scan forward only mov al, EOS ; character to search for mov cx, di ; where are we now not cx ; what's left in segment - 1 push cx ; save char count repne scasb je SHORT @@Done scasb ; test final char dec cx ; avoids trouble with "not" below @@Done: pop ax ; get original count sub cx, ax ; subtract current count not cx ; and invert it popf ; restore df dec di cmp [BYTE PTR es:di], EOS je SHORT @@Fin ; cf = 0 if equal stc ; set cf => error @@Fin: pop di ax ret ENDP strlen END