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Assembly Source File | 1988-11-20 | 14.8 KB | 398 lines

COMMENT \ Filter TOPS-20 sequence numbers from the standard input file. These consist of sequences nnnn<Bn><09> at the beginning of each line. That is, the fifth character is a digit <3n> which has been OR'ed with <80>. This is how Kermit flags the fifth character from a DEC-20 36-bit word in which the rightmost bit is 1. Trailing blanks are also trimmed. If any single line is longer than the internal line buffer size (256), it will be output unprocessed and a warning message will be issued. This should be rare, and if the number of occurrences is small, hand editing of the output file could fix the problem. Usage: deseq <inputfile >outputfile Error return codes: 0 - normal termination 1 - write error on standard output file (usually because disk full); an error message is printed. {Adapted from a disassembly of the IBM utility MORE.COM and commented with a view to being a model for further simple filters.} For efficiency, input and output characters are handled in large buffers. [28-Jan-84] \ assume cs:deseqc,ds:deseqc,es:deseqc,ss:deseqc deseqc segment para public 'code' include dos.inc include ascii.inc org 100h ; this is a .COM file DEBUG equ 0 ; non-zero for built-in input file test ; Sum of buffer sizes can be 64K-(code + otherdata size), or about 40K total MAXOUTBUF equ 16384 ; Output buffer size MAXINBUF equ 16384 ; Input buffer size MAXLINBUF equ 256 ; Line buffer size deseq proc near call check_dos_version if DEBUG mov dx,offset debugfn mov al,$DOS_OPEN2_READ mov ah,$DOS_OPEN2 int $DOS jnc openok int $HALT ; open failure openok: mov debugin,ax ; save file handle endif mov inbuf_prev,0 ; set empty input buffer mov inbuf_len,0 ; set empty input buffer mov linbuf_len,0 ; set empty line buffer mov outbuf_len,0 ; set empty output buffer readln: call get_line ; get an input line mov cx,linbuf_len ; Get output line length jcxz eof ; No more data, all done call strip_line ; Yes, go strip any line number putlin: call trim_line call write_line ; go write the line jmp short readln ; Loop for next line eof: ; here at end-of-file call write_buf ; write any remaining data mov ah,$DOS_EXIT ; all done, no more data mov al,0 ; return code int $DOS ; terminate if DEBUG even ; align on word boundary debugin dw ? debugfn db "c:\pascal\foo.for",.NUL endif even ; align on word boundary inbuf_prev dw ? ; Buffer pointer inbuf_len dw ? ; Buffer size inbuf db MAXINBUF dup (?) ; Input buffer even ; align on word boundary linbuf_len dw ? ; Buffer pointer linbuf db MAXLINBUF dup (?) ; Output buffer for line storage even ; align on word boundary outbuf_len dw ? ; Buffer length outbuf db MAXOUTBUF dup (?) ; Output buffer for final write deseq endp assume cs:deseqc,ds:deseqc,es:deseqc,ss:deseqc trim_line proc near ; Routine to trim trailing white space from line. No action is taken if ; the line buffer does not end with CR LF, since in that case, the line ; is incomplete (long line split across buffer boundary). ; No registers are preserved mov cx,linbuf_len ; line length mov si,offset linbuf-3 ; output buffer address-3 add si,cx ; address of last character before CR LF mov al,[si+1] ; get what should be CR cmp al,.CR ; was it? jne notrim ; no, not really end-of-line mov al,[si+2] ; get what should be LF cmp al,.LF ; was it? jne notrim ; no, not really end-of-line std ; set direction flag to decrement si trim: lodsb ; byte from [si] to al, decrement si cmp al," " ; blank? je zap_space ; yes cmp al,.HT ; tab? jne notrim ; no, not white space, so exit loop zap_space: mov byte ptr [si+1],.NUL ; change blank or tab to NUL loop trim ; decrement cx and loop until cx = 0 notrim: ret ; return to caller trim_line endp assume cs:deseqc,ds:deseqc,es:deseqc,ss:deseqc strip_line proc near ; Routine to strip line numbers ; No registers are preserved mov cx,linbuf_len ; line length cmp cx,8 ; Possible nnnnn<TAB> .. <CR><LF> on this line? jle strip_done ; No, return immediately mov si,offset linbuf; line buffer address cld ; clear direction flag to increment si nextch: ; Loop looking for line numbers lodsb ; Byte from [si] to al, increment si cmp al,128 ; 8-th bit on? jb ordchr ; Jump if not call check_seq ; Check for sequence number and clear if so ordchr: ; Ordinary character loop nextch ; Decrement count in cx and loop until cx = 0 strip_done: ret ; return to caller strip_line endp assume cs:deseqc,ds:deseqc,es:deseqc,ss:deseqc get_line proc near ; Routine to get a line from the standard input file, leaving it ; in line_buf with its length in line_len. line_len will be zero ; on end-of-file. ; no registers preserved getnext: call getch ; get next input character jz eol ; zero when no more input push ax ; save character call write ; save in line buffer pop ax ; restore character cmp al,.LF ; end-of-line yet? jne getnext ; jump if not LF eol: ; here on eol or possibly eof ret ; return to caller get_line endp assume cs:deseqc,ds:deseqc,es:deseqc,ss:deseqc check_dos_version proc near ; Routine to check for DOS version 2.00 or later. Aborts with message ; if not so. ; No registers preserved mov ah,$DOS_GETVERSION int $DOS xchg ah,al cmp ax,0200h ; DOS 2.00 or later? jnb cont ; jump if version >= 2.00 mov dx,offset baddos mov ah,$DOS_STROUT int $DOS ; print string to standard output int $HALT ; terminate early version of DOS cont: ret baddos db "DESEQ: Incorrect DOS version" db " -- must run under DOS 2.00 or later" db .CR,.LF,"$" check_dos_version endp assume cs:deseqc,ds:deseqc,es:deseqc,ss:deseqc getch proc near ; Routine to get next character from standard input in al. ; Returns with zero flag set on end-of-file, clear otherwise ; No registers are preserved mov bp,inbuf_prev ; Pointer to next available byte in buffer cmp bp,inbuf_len ; Bytes left in buffer? jl noread ; Yes, no need to read more yet mov ah,$DOS_READ2 ; string read code if DEBUG mov bx,debugin ; file handle else mov bx,$STDIN ; file handle endif mov cx,MAXINBUF ; count of bytes to read mov dx,offset inbuf ; buffer address int $DOS ; read a block of characters mov inbuf_len,ax ; number of bytes actually read mov inbuf_prev,0 ; Point to last byte returned or ax,ax ; test number of bytes obtained jz done ; return with zero flag set on EOF noread: mov bp,inbuf_prev ; offset of next character available mov al,inbuf[bp] ; get the character from the buffer inc inbuf_prev ; increment byte pointer (and set condition ; flag to non-zero) done: ret ; return to caller with zero/non-zero flag set getch endp assume cs:deseqc,ds:deseqc,es:deseqc,ss:deseqc write proc near ; Routine to write the character in al to the line buffer. If the ; buffer is filled, it is automatically written to the standard ; output file by a call to write_line and an error message is issued ; noting the overflow. Characters are not lost in the output, but ; processing on the current line will not be correct. ; No registers are preserved mov bp,linbuf_len ; offset of next available slot in buffer cmp bp,MAXLINBUF ; buffer full yet? jl nowrite ; no, just add to buffer push ax ; yes, save character call write_line ; then write the buffer push bx ; save registers push cx push dx mov ah,$DOS_WRITE2 ; and write an error message mov bx,$STDERR mov cx,linemsg_len mov dx,offset linemsg int $DOS pop dx ; restore registers pop cx pop bx pop ax ; and restore the character mov bp,0 ; new output buffer length in index register mov linbuf_len,bp ; and storage nowrite: ; here with bp pointing to offset of next char mov linbuf[bp],al ; save the character inc linbuf_len ; increment output buffer length ret ; return to caller linemsg db "%Long line overflows buffer - processing incomplete",.CR,.LF linemsg_len equ $-linemsg write endp assume cs:deseqc,ds:deseqc,es:deseqc,ss:deseqc write_line proc near ; Routine to write the line buffer to the output buffer. Any NUL's found ; are discarded. ; No registers are preserved. mov cx,linbuf_len ; current line length jcxz wrdone ; exit if no characters left to write mov si,offset linbuf; line buffer address mov bx,outbuf_len ; old output buffer length lea di,outbuf[bx] ; address of next available char in output cld ; clear direction flag to increment si and di mvbuff: ; copy the buffer discarding NULs lodsb ; character from [si] to al, increment si cmp al,.NUL ; NUL? je mvloop ; yes, skip output cmp bx,MAXOUTBUF ; still space in output buffer? jl mvchar ; yes, store the character call write_buf ; no, empty the buffer mov bx,outbuf_len ; old output buffer length mvchar: stosb ; character from al to [di], increment di inc bx ; count the character mvloop: loop mvbuff ; decrement cx, and loop while cx > 0 wrdone: mov outbuf_len,bx ; update output buffer length mov linbuf_len,0 ; indicate empty buffer ret ; return to caller write_line endp assume cs:deseqc,ds:deseqc,es:deseqc,ss:deseqc write_buf proc near ; Routine to write outbuf buffer to the standard output file. ; All registers are preserved. ; Error returns from DOS (e.g. disk full) result in an error message ; and immediate termination. push ax ; save registers push bx push cx push dx mov ah,$DOS_WRITE2 mov bx,$STDOUT ; file handle mov cx,outbuf_len ; count of bytes to write jcxz writeok ; exit if nothing to write mov dx,offset outbuf; buffer address int $DOS ; write the buffer jnc writeok mov ah,$DOS_WRITE2 ; write failed, issue message mov bx,$STDERR ; file handle mov cx,writemsg_len ; count mov dx,offset writemsg ; buffer int $DOS mov ah,$DOS_EXIT mov al,1 ; return code int $DOS ; abort writeok: mov outbuf_len,0 ; show empty buffer pop dx ; restore registers pop cx pop bx pop ax ret writemsg db "?Unrecoverable write error on standard output file",.CR,.LF db " Disk probably full",.CR,.LF writemsg_len equ $-writemsg write_buf endp assume cs:deseqc,ds:deseqc,es:deseqc,ss:deseqc check_seq proc near ; Routine to check that we have 5 digits followed by a tab, and if ; so, replace it by NULs. On entry, si points to character FOLLOWING ; one with bit 8 set, and al contains the latter character. ; Preserves all registers push bx ; save bx push ax ; and ax cmp byte ptr [si],.HT ; check for following tab jne check_done ; jump if not tab mov bx,-5 ; loop count check_dig: ; loop testing for digits mov al,[si+bx] ; get digit cmp bx,-1 ; digit before tab? jne no_clear ; jump if not and al,7FH ; yes, clear high bit - nnnnN<tab> no_clear: cmp al,.DIGIT0 jb check_done ; not a digit cmp al,.DIGIT9 ; ja check_done ; not a digit inc bx ; was digit, bx = bx + 1 jl check_dig ; loop until bx = 0 mov byte ptr [si-5],.NUL ; set the nnnnn<TAB> field to NULs mov byte ptr [si-4],.NUL mov byte ptr [si-3],.NUL mov byte ptr [si-2],.NUL mov byte ptr [si-1],.NUL mov byte ptr [si],.NUL check_done: pop ax ; restore ax pop bx ; restore bx ret ; return to caller check_seq endp deseqc ends end deseq