Power-Programmierung/CD1.mdf/magazine/pcmagazi/1990/16/cmdedit.asm

Assembly Source File | 1990-06-26 | 47KB | 1,747 lines

;
; CMDEDIT.ASM
;(c) 1989, 1990 PC Magazine and Ashok P. Nadkarni
;

SIGNATURE1 equ <"CMDEDIT 2.0 (c) 1990 Ziff Communications Co.">
SIGNATURE2 equ <"PC Magazine">
SIGNATURE3 equ <"Ashok P. Nadkarni">

; Main module for command line editor.

    INCLUDE common.inc
    INCLUDE general.inc
    INCLUDE ascii.inc
    INCLUDE buffers.inc
    INCLUDE dos.inc
    INCLUDE bios.inc

    PUBLIC    dos_version_major
    PUBLIC    dos_version_minor
    PUBLIC    resident
    PUBLIC    macro_level
    PUBLIC    cur_macro
    PUBLIC    cur_macro_len
    PUBLIC    linebuf
    PUBLIC    linelimit
    PUBLIC    dot
    PUBLIC    lastchar
    PUBLIC    LINEBUF_END
    PUBLIC    edit_mode
    PUBLIC    default_imode
    PUBLIC    caller_cursor
    PUBLIC    omode_cursor
    PUBLIC    pgm_name
    PUBLIC    macrosize
    PUBLIC    symsize
    PUBLIC    dossize
    PUBLIC    dirsize
    PUBLIC    mfilename
    PUBLIC    mfile_seen
    PUBLIC    macro_ignore_char
    PUBLIC    cmdlen
    PUBLIC    silent
    PUBLIC    endm_cmd
    PUBLIC    defs
    PUBLIC    defm
    PUBLIC    tsr_install_end
    PUBLIC    source
    PUBLIC    abort_processing
    PUBLIC    disp_line
    PUBLIC    set_disp_marks
    PUBLIC    insert_at_dot
    PUBLIC    insert_chars
    PUBLIC    remove_chars
    PUBLIC    erase_to_dot
    PUBLIC    init_over
    PUBLIC    line_to_scr
    PUBLIC    get_next_line
    PUBLIC    reset_line
    PUBLIC    in_appl
    PUBLIC    user_command
    PUBLIC    our_break_handler
    PUBLIC    prev_isr1b
    PUBLIC    old_int21vec
    PUBLIC    cmdedit_isr
    PUBLIC    makeroom
    PUBLIC    locate_dosenv
    PUBLIC    cmdedit

    IFE    TSR
    PUBLIC    cmdedit_cmd
    PUBLIC    debug_loop
    PUBLIC    freadline
    PUBLIC    get_file_line
    PUBLIC    read_cmdfile
    PUBLIC    disp_prompt
    PUBLIC    prompt
    PUBLIC    init_screen
    ENDIF


DGROUP    GROUP    CSEG

CSEG    SEGMENT    PARA PUBLIC 'CODE'
    EXTRN    install_begin:BYTE
    EXTRN    install:PROC
    EXTRN    execute_defs:PROC
    EXTRN    execute_defm:PROC
    EXTRN    execute_dels:PROC
    EXTRN    execute_delm:PROC
    EXTRN    execute_cmdstat:PROC
    EXTRN    execute_pushd:PROC
    EXTRN    execute_popd:PROC
    EXTRN    execute_chd:PROC
    EXTRN    hist_init:PROC
    EXTRN    hist_type:PROC
    EXTRN    hist_top:PROC
    EXTRN    dirs_init:PROC
    EXTRN    macro_init:PROC
    EXTRN    symbol_init:PROC
    EXTRN    expand_macro:PROC
    EXTRN    expand_symbol:PROC
    EXTRN    get_macro_line:PROC
    EXTRN    skip_whitespace:PROC
    EXTRN    skip_nonwhite:PROC
    EXTRN    stre_cmp:PROC
    EXTRN    get_kbd_line:PROC
    EXTRN    getargs:PROC
    EXTRN    file_error:BYTE
    EXTRN    abort_install:PROC
    EXTRN    expand_var:PROC
    EXTRN    execute_rsthist:PROC
    EXTRN    execute_rstmac:PROC
    EXTRN    execute_rstsym:PROC
    EXTRN    execute_rstdir:PROC

; Define important fields in the PSP.
    ASSUME    CS:DGROUP
    ORG    2Ch
env    dw    ?    ;Segment of environment block

    ORG    80h
PROMPT_BUF_SIZE EQU 80
prompt    LABEL    BYTE    ;buffer used for prompt after TSRing
cmdlen    DB    ?    ;Offset 80h in the PSP contains length of command
;             line when program is invoked

    ORG    80h+PROMPT_BUF_SIZE
prompt_length    dw    ?
cur_macro LABEL    BYTE    ;Start of area used after TSRing to
;             store the current macro expansion.


    ASSUME    CS:DGROUP,DS:DGROUP,ES:DGROUP,SS:DGROUP
    ORG    100h
entry:    jmp    install

; The following variables are LOST after TSRing since the space is
; reused for other purposes.

mfilename    db    64 DUP (0)    ;Storage for ASCIIZ filename
mfile_seen    db    0        ;Indicate if command line
;                     specified an init file
mfile_handle    dw    ?        ;Handle for open file

; Entry init_over is jumped to from the installation code after all the
; command line parsing has been done. This part of the installation
; remains resident. It is not kept with the install code because that
; code sections gets overwritten with various buffers.

init_over proc    near

; The command parameters have been parsed. Now get ready to terminate.
    mov    si,offset DGROUP:install_begin
                    ;First location in installation code
    mov    bx,si            ; is where the buffers start.
    mov    ax,dossize        ;Size of DOS history buffer
    add    si,ax            ;SI <- end of DOS buffer
    xor    cx,cx            ;Indicate DOS mode
    call    near ptr hist_init    ;Initialize DOS history buffer
    mov    bx,si            ;Repeat for directory stack
    mov    ax,dirsize
    add    si,ax
    call    near ptr dirs_init
    mov    bx,si            ;And finally for the macros
    mov    ax,macrosize
    add    si,ax
    call    near ptr macro_init
    mov    bx,si            ;And finally for the macros
    mov    ax,symsize
    add    si,ax
    call    near ptr symbol_init

    ; SI->end of buffer area
; Read in the command file
    call    near ptr init_screen     ;Need to do this because
;                     reset_line (called by
;                     execute_defm) restores cursor shape.
    call    near ptr read_cmdfile

; Initialize var source to get the next line from the keyboard.
    mov    source,offset DGROUP:get_kbd_line
; All data structures initalized. Now setup stack pointer, release
; unneeded memory back to DOS, set up interrupt handler and TSR.
    push    es            ;save ES
    mov    es,env            ;Don't need environment block
    ASSUME    ES:NOTHING
    mov    ah,49h
    int    21h            ;Release the block
    IF    TSR
    mov    ax,3521h        ;Get old interrupt vector
    int    21h
    mov    old_int21vec,bx        ;Remember offset
    mov    old_int21vec+2,es        ;Remember segment

    mov    dx,offset DGROUP:cmdedit_isr ;Our handler
                    ;DS = CS already
    mov    ax,2521h        ;Set intr vector
    int    21h
    ENDIF
    pop    es            ;Restore ES
    ASSUME    ES:DGROUP

    lea    dx,STACK_SIZE+15[si]    ;Calculate end of TSR portion
;                     DX<-num bytes to keep resident
    and    dl,0f0h            ;    rounded to para
;     Note DX->BEYOND last byte of program
    mov    new_sp,dx        ;Remember it

    mov    resident,1        ;Indicate we're TSR

    IFE    TSR
; Don't actually TSR
debug_loop:
@init_over_10:
    @DispCh    CR
    @DispCh    LF
    lea    dx,dummy_prompt
    @DispStr dx
    mov    dx,offset DGROUP:debug_buf     ;Offset
    mov    debug_buf,DEBUG_BUFSIZE-2
    mov    ah,0Ah            ;Function code
    pushf                ;Simulate interrupt
    push    cs            ;Simulate interrupt
    call    near ptr cmdedit_isr    ;Simulate interrupt
    jmp    short @init_over_10    ;Keep looping
debug_buf    db    256 DUP (?)
DEBUG_BUFSIZE    equ $-debug_buf
dummy_prompt    db    "dummy>",DOLLAR
    ENDIF

    int    27h            ;TSR
init_over endp


;+
; FUNCTION : read_cmdfile
;
;    Reads commands from a file. The filename is in the variable
;    mfilename. The space occupied this function is overwritten
;    after TSRing so it must NOT be called once the program is resident.
;
; Parameters:
;    None.
;
; Returns:
;    AX =    0 on success, any other value if failure
;
; Register(s) destroyed:
;    AX,BX,CX,DX
;-
read_cmdfile proc near
    @save    si,di
    cmp    mfile_seen,0
    je    @read_cmdfile_100    ;No file specified

    @OpenFil mfilename,0
    jc    @read_cmdfile_92    ;CF=1 for errors
@read_cmdfile_30:
    mov    source,offset DGROUP:get_file_line
;                    We want get_next_line to read
;                    from the file.
    mov    mfile_handle,ax        ;Save file handle

@read_cmdfile_50:
    mov    dx,offset DGROUP:linebuf ;Destination for file line
    mov    ax,LINEBUF_SIZE
    call    near ptr freadline    ;Get next line into buffer
                    ;AX contains line length
    jnc    @read_cmdfile_80    ;no error or EOF
    or    ax,ax            ;No more bytes ?
    jz    @read_cmdfile_99    ;EOF is not error
    jmp    short @read_cmdfile_90    ;Error, abort install
@read_cmdfile_80:
    mov    dx,offset DGROUP:linebuf
    add    dx,ax
    mov    lastchar,dx        ;Update end of line
    call    near ptr cmdedit_cmd    ;Execute as a command
    jnc    @read_cmdfile_50    ;If not a command, better be a
;                     blank line
    call    near ptr blankline
    jnc    @read_cmdfile_50    ;Ignore blank lines
;     If not blank line and not CMDEDIT command, then error error handler

@read_cmdfile_90:
; Come here for error
    @ClosFil mfile_handle        ;Close the file
@read_cmdfile_92:
    @DispStr file_error
    mov    ax,-1            ;Indicate exit code
    jmp    abort_install        ;Exit program

@read_cmdfile_99:
    @ClosFil mfile_handle        ;Close the file
    jc    @read_cmdfile_92    ;Abort if error closnig file
@read_cmdfile_100:
    @restore
    ret
read_cmdfile endp



;+
; FUNCTION : get_file_line
;
;    Called indirectly through the global variable 'source'.
;    Currently this routine exists only during installation and must
;    NOT be called once the program is a TSR. The next line from the
;    file is copied to linebuf. If there is no next line, the
;    installation is aborted.
;
; Parameters:
;    None.
;
; Returns:
;    Nothing.
; Register(s) destroyed:
;    AX,BX,CX,DX
;-
get_file_line proc near
    mov    dx,offset DGROUP:linebuf
    mov    ax,LINEBUF_SIZE
    call    near ptr freadline
    jnc    @get_file_line_99
;Error reading file or EOF
    @DispStr file_error
    jmp    abort_install
@get_file_line_99:
    mov    dx,offset DGROUP:linebuf
    add    dx,ax
    mov    lastchar,dx        ;Update end of line
    ret
get_file_line    endp




;+
; FUNCTION : freadline
;
;    Reads a line at a time from the file whose handle is in
;    mfile_handle into the buffer pointed to by AX. If the buffer is
;    too small or if there are any errors, the routine returns with CF set.
;    If EOF, then AX = 0 and CF is set.
;
; Parameters:
;    DX    = address of buffer
;     AX    = size of buffer
;
; Returns:
;    CF     = 0 if no errors (and not EOF), else 1.
;    AX    = num chars in line if CF = 0.
;          0 if EOF, ffff for other errors if CF = 1
;
; Register(s) destroyed:
;-
freadline proc    near
    @save    si,di
    mov    di,dx            ;DI->buffer
    mov    bx,mfile_handle
    mov    si,ax            ;SI<-num bytes to read
    xchg    cx,ax            ;CX<-num bytes to read
    mov    ah,3Fh            ;File read function
    int    21h
    jc    @freadline_99        ;Error!
    mov    cx,ax            ;CX<-num bytes read
    jcxz    @freadline_99_a        ;EOF (note AX is 0 indicating EOF)
    xchg    dx,ax            ;DX<-num bytes read
    mov    bx,di            ;BX->start of buffer
    mov    al,CR
    repne    scasb            ;Hunt for CR
    je    @freadline_50        ;Found
;    No CR found, this better be the last line in file.
    cmp    dx,si            ;Were fewer bytes read than requested?
    cmc
    jc    @freadline_99        ;Error
    push    dx            ;Save length of line
    xor    ax,ax            ;AX<-num extra bytes read
    jmp    short @freadline_60
@freadline_50:
    stc                ;Assume line too long
    jcxz    @freadline_99        ;error if match in last char
;                     (line too long)
    cmp    BYTE PTR [di],LF    ;Next char must be linefeed
    stc                ;Assume error
    jne    @freadline_99        ;Indeed an error if not LF
    mov    ax,di
    sub    ax,bx            ;AX<-num chars including CR
    sub    dx,ax
    xchg    ax,dx
    dec    dx            ;DX<-num chars in line
    dec    ax            ;AX<-num extra chars read
    push    dx            ;Save num chars in line

@freadline_60:
; Top of stack contains num bytes in line.
; Now position file pointer to 'unread' characters.
; AX contains the num of extra characters read.
    neg    ax
    cwd
    mov    cx,ax
    xchg    cx,dx            ;CX:DX<-num bytes to 'unread'
    mov    bx,mfile_handle
    mov    ax,4201h        ;Move file ptr relative
    int    21h            ;Seek file relative
; CF set/reset by error status
    pop    ax            ;AX<-num bytes in line
    clc                ;No errors
    jmp    short @freadline_100
@freadline_99:
    mov    ax,0ffffh        ;Non-EOF error
@freadline_99_a:
    stc                ;Indicate error or EOF
@freadline_100:
    @restore
    ret
freadline endp



;+
; FUNCTION : blankline
;
;    Checks whether the line in linebuf is blank or not. Also treats it
;    as blank line if it begins with a `-'.
;
; Parameters:
;    None.
;
; Returns:
;    CF    = 0 if blank line, else 1.
; Register(s) destroyed:
;    AX,BX,CX,DX
;-
blankline proc    near
    @save    si
    mov    si,offset DGROUP:linebuf
    cmp    byte ptr [si],'-'        ;Comment char ?
    jne    @blankline_20
    clc
    jmp    short @blankline_99
@blankline_20:
    mov    cx,lastchar
    sub    cx,si            ;CX<-num chars in line
    call    near ptr skip_whitespace ;CF=1 if end of string
    cmc
@blankline_99:
    @restore
    ret
blankline endp


; Extend the resident part of the installation code to form a buffer to
; hold the prompt and one to hold the current macro line arguments.
;  - 128 bytes from PSP + initial portion of CSEG.
tsr_install_end LABEL BYTE
    IF    ($-entry) LT (2+PROMPT_BUF_SIZE+LINEBUF_SIZE - 128)
    DB    (2+PROMPT_BUF_SIZE+LINEBUF_SIZE - 128 - ($-entry)) DUP (?)
    ENDIF

pgm_name   db    SIGNATURE1,CR,LF
copyrite   db    SIGNATURE2,32,254,32,SIGNATURE3,CR,LF,LF,DOLLAR,26

; Major and minor DOS versions.
dos_version_major    db    ?
dos_version_minor    db    ?

;dos_envseg    dw    0            ;Segment for DOS
;                         environment. 0 indicates
;                         we don't know it.

resident    db    0        ;1 after becoming resident
abort_entry_stack dw ?            ;Storage for stack state to be
;                     restored when processing is aborted
abort_msg_hd db    '*** CMDEDIT : '    ;Header for abort message
ABORT_HDR_LEN    equ $-abort_msg_hd
abort_msg_tl db ' Any ongoing macro aborted! ***'            ;Tail for abort message
ABORT_TAIL_LEN    equ $-abort_msg_tl

; The following are error messages displayed by routine abort_processing.
; ALL MESSAGES MUST BE SHORT ENOUGH TO FIT INTO LINEBUF TOGETHER WITH
; abort_msg_hd and abort_msg_tl. The order of messages must be same as
; the order of Error code definitions in file common.inc
abort_msg_table LABEL    BYTE
line_trunc_msg     db    'Line too long.'
saw_sig_msg     db    'Command aborted by user.'
dirstk_empty_msg db    'Directory stack empty.'
dirstk_msg     db    'Invalid dir or stack full.'
dirstk_only_dos     db    'Command is DOS only.'
nested_macro_msg db    'Nested macro definition.'
nested_delm_msg     db    'DELM used inside macro.'
ctrl_brk_msg     db    'Control-Break.'
abort_msg_end    LABEL    BYTE

; The following table holds pointers to each entry in the message table
; above. The length of each message is also stored here.
abort_msg_ptrs    LABEL    WORD
        dw    line_trunc_msg
        dw    saw_sig_msg-line_trunc_msg
        dw    saw_sig_msg
        dw    dirstk_empty_msg-saw_sig_msg
        dw    dirstk_empty_msg
        dw    dirstk_msg-dirstk_empty_msg
        dw    dirstk_msg
        dw    dirstk_only_dos-dirstk_msg
        dw    dirstk_only_dos
        dw    nested_macro_msg-dirstk_only_dos
        dw    nested_macro_msg
        dw    nested_delm_msg-nested_macro_msg
        dw    nested_delm_msg
        dw    ctrl_brk_msg-nested_delm_msg
        dw    ctrl_brk_msg
        dw    abort_msg_end-ctrl_brk_msg

macrosize    dw    512    ;Default size of macro buffer
symsize        dw    512    ;Default size of symbol buffer
dossize        dw    512    ;Default size of DOS history buffer
dirsize        dw    128    ;Default size of directory stack buffer

;+-------------------------+
;| CMDEDIT state variables |
;+-------------------------+
; The variables source and macro_level together indicate the source of
; the next line. If macro_level is non-zero, the next line is obtained
; from an ongoing macro expansion. If macro_level is 0, then the
; variable source contains the address of the function to call to
; return the next line. This will be either get_kbd_line or
; get_file_line.
macro_level    dw    0
source        dw    ?        ;filled in during initialization


;+----------------------------------------------------------+
;| CMDEDIT commands. All commands preceded by a length byte.|
;| For each command that is added, make sure you update the |
;| table cmd_func_table below.                    |
;+----------------------------------------------------------+
cmd_table    LABEL    BYTE
defs        db    4,'defs'    ;Define a single line macro
defm        db    4,'defm'    ;Start multiline macro definition
pushd        db    5,'pushd'    ;Push on directory stack
popd        db    4,'popd'    ;Pop from directory stack
chd        db    3,'chd'        ;Change disk and directory
dels        db    4,'dels'    ;Delete a symbol
delm        db    4,'delm'    ;Delete a macro
rsthist        db    7,'rsthist'    ;Reset history stack
rstmac        db    6,'rstmac'    ;Reset macro buffer
rstsym        db    6,'rstsym'    ;Reset symbol buffer
rstdir        db    6,'rstdir'    ;Reset directory stack
cmdstat        db    7,'cmdstat'    ;Show macro and symbol status

cmd_table_end    db    0        ;Terminate with a 0
MAX_CMD_LEN    equ    7        ;Length of longest command
; Note endm is not a command except during a macro definition.
endm_cmd    db    4,'endm'    ;End multiline macro definition


;+--------------------------------------------------------------+
;| CMDEDIT command functions. Must be in same order as commands.|
;+--------------------------------------------------------------+
cmd_func_table    label WORD
        dw    execute_defs
        dw    execute_defm
        dw    execute_pushd
        dw    execute_popd
        dw    execute_chd
        dw    execute_dels
        dw    execute_delm
        dw    execute_rsthist
        dw    execute_rstmac
        dw    execute_rstsym
        dw    execute_rstdir
        dw    execute_cmdstat

linebuf_prefix    db    0        ;Fill byte/Sentinel before linebuf.
;                     Used in code to allow uniform
;                     checking of first linebuf character.
linebuf        db    LINEBUF_SIZE DUP (?)    ;Temporary line buffer.
LINEBUF_END    equ    $
linebuf_suffix    db    ?            ;Need a byte at end of
;                         linebuf in various places
macro_ignore_char db    ';'        ;Character used to prevent macro
;                     and symbol expansion.
lastchar    dw    ?        ;Points beyond last char in the line
cur_macro_len    dw    ?        ;Length of data in cur_macro
dot        dw    ?        ;Current position in line
disp_begin    dw    ?        ;disp_begin and disp_end are
disp_end    dw    ?        ; markers into the line buffer
;                      that are used to keep track
;                      of the range that has been
;                      changed. This is used to
;                      selectively update the display.
edit_mode    db    ?        ;1 if insert mode, else 0
default_imode    db    0        ;By default overtype mode

linelimit    dw    ?        ;Upper limit for linebuf based
;                     on user's buffer length
noted_dos_seg    db    0        ;1 after we have noted DOS segment
dos_seg        dw    ?        ;Stores DOS segment
in_appl        db    0        ;0 if dos, 1 if application
user_command    db    0        ;This is set to 1 by certain
;                     CMDEDIT commands to return a
;                     string to the caller.
;                     (Basically put in as a kluge
;                     to get the prompt right after
;                     a pushd/popd/chd)
;+------------+
;| Video data |
;+------------+
video_page    db    ?        ;Current video page
screen_width    db    ?        ;width of screen
initial_curcol    label    byte        ;initial cursor column
initial_curpos    dw    ?        ;Initial cursor position
;Next two words must be contiguos
omode_cursor    dw    ?        ;Cursor for overtype mode
imode_cursor    dw    ?        ;Cursor for insert mode
caller_cursor    dw    ?        ;Cursor shape of caller

silent        db    0        ;non-0 if bell should not be rung

;+-------------------------------------------------------------------------+
;|Storage areas for various registers when called through INT 21 interface.|
;+-------------------------------------------------------------------------+

ssreg    dw    ?
spreg    dw    ?

old_int21h LABEL DWORD        ;Storage for previous int 21h vector
old_int21vec    DW    2 DUP (?)

new_sp    dw    ?        ;Store our stack ptr (bottom of stack).
                ;This is first para BEYOND cmdedit's memory.

prev_isr1b    dd    ?        ;Previous control break handler

; check_break is set to 1 on entry to cmdedit, and restored to 0 on exit. If
; 1 on entry, then calling program must have been aborted with a break or
; critical error. The CMDEDIT Ctrl-Break ISR increments this flag every
; time it is called. If it is > 1, inside CMDEDIT, it indicates that a
; ctrl-break was entered. This allows runaway macros and symbols to be
; aborted.
check_break    dw    0
trap_break    db    0        ;If 1, does not allow original
;                     Ctrl-Break handler to see the
;                     Ctrl_break



;+
; FUNCTION : cmdedit_isr
;
;    This is our replacement for the DOS INT 21h handler.
;
; Parameters:
;    AH = function code
;
; Register(s) destroyed:
;-
cmdedit_isr proc far
    ASSUME    CS:DGROUP,DS:NOTHING,ES:NOTHING,SS:NOTHING
    pushf                ;Save flags
    cmp    ah,0Ah            ;Is it the buffered input function ?
    je    @cmdedit_isr_10        ;If so go on carry out our duty
    popf                ;else restore flags
    jmp    cs:old_int21h        ;and execute the original ISR
@cmdedit_isr_10:
                    ;Save registers
    mov    cs:ssreg,ss        ;Stack segment
    mov    cs:spreg,sp        ; and pointer
    cli                ;Wanna change stack
    push    cs
    pop    ss
    mov    sp,cs:new_sp        ;Bottom of stack
    ASSUME    SS:DGROUP
    sti                ;OK to interrupt now
    @save    ax,bx,cx,dx,si,di,bp,ds,es
    xchg    bx,dx
    mov    al,byte ptr ds:[bx]    ;Length of caller buffer
    xchg    dx,bx
    xor    ah,ah            ;AX<-length of caller's buffer
    push    ds            ;Save user segment
    mov    cx,cs
    mov    ds,cx            ;Init DS, ES to point to DGROUP
    mov    es,cx
    ASSUME    DS:DGROUP,ES:DGROUP
    add    ax,offset dgroup:linebuf ;AX->last allowable linebuf
;                      location + 1
    dec    ax            ;Need room for CR at end of line
    mov    linelimit,ax        ;Store it
    pop    ax            ;AX <- User's buffer segment
                    ;DX already contains offset of
                    ; user buffer
    call    near ptr cmdedit    ;Main routine
    @restore
    cli
    mov    ss,cs:ssreg
    mov    sp,cs:spreg
    sti

    popf
    iret
cmdedit_isr    endp




;+
; FUNCTION : cmdedit
;
;    Main routine called by the INT 21h ISR to get next line.
;    General Algorithm:
;    (1) Get the next line from the keyboard/macro expansion/file.
;    (2) Check for line begins with a macro. If so, expand it and
;        repeat step (2). Else go onto step (3).
;    (3) Check if the line is an internal CMDEDIT command. If so, execute
;        it and return to step (1).
;    (4) Copy line to caller's buffer and return.
;
; Parameters:
;    AX    = segment of user's buffer
;    DX    = offset of user's buffer
;
; Returns:
;    The next input line is copied into the user's buffer.
; Register(s) destroyed:
;    All except segment registers.
;-
cmdedit    proc    near
    push    es            ;Save ES
    push    ax            ;Caller's buffer segment
    push    dx            ;Caller's buffer offset
    mov    trap_break,1        ;Trap Ctrl-Break handler
    mov    cx,1
    xchg    cx,CS:check_break    ;Check if last call did not
;                     exit normally. Also set flag
;                     for this call.
    jcxz    @cmdedit_0        ;Last exit was OK
    mov    macro_level,0        ;No it was not, so reset input
    mov    source,offset DGROUP:get_kbd_line
@cmdedit_0:
    call    near ptr init_screen    ;Get screen/cursor data

    cmp    noted_dos_seg,0        ;Have we noted the DOS segment ?
    jne    @cmdedit_1        ;Jump if we know it already
    mov    noted_dos_seg,1        ;Remember that we now know it
    mov    dos_seg,ax        ;Else remember it
                    ;No point jumping over next
                    ;couple of statements.
@cmdedit_1:
    mov    cx,1            ;Assume caller is not DOS
    cmp    ax,dos_seg        ;Is the caller DOS ?
    jne    @cmdedit_2
    dec    cx            ;Yes, CX<-0
@cmdedit_2:
    mov    in_appl,cl        ;Rememeber whether caller is dos
    call    near ptr hist_type    ;Set the history type (DOS/appl)

; cmdedit_abort_entry is the entry point when command proessing is
; aborted for any reason. It is jumped to from abort_processing
    mov    abort_entry_stack,sp    ;Remember stack state
cmdedit_abort_entry    LABEL PROC
@cmdedit_3:
    call    near ptr reset_line    ;Reset cursor, line etc.
    call    near ptr get_next_line    ;Get the next line from appropriate
;                     source (stored in linebuf)
@cmdedit_10:
    cmp    check_break,2        ;Check for any control breaks
    jb    @cmdedit_11        ;No ctrl-breaks
    mov    check_break,1
    mov    ax,E_CTRL_BREAK        ;Message number
    jmp    abort_processing

@cmdedit_11:
;If the first character is a ignore character, do not do a macro or symbol
;expansion.
    mov    cx,lastchar        ;End of line
    mov    si,offset DGROUP:linebuf ;SI->line buffer
    sub    cx,si            ;CX<-length of line
    jcxz    @cmdedit_15        ;Empty line, keep going since it
;                     can still be a macro or symbol
    mov    al,[si]            ;AL<-first char of line
    cmp    al,macro_ignore_char
    jne    @cmdedit_15
; First is an ignore character so move up all characters and return
    mov    di,si            ;DI->start of line
    inc    si            ;SI->first char to copy
    dec    cx            ;1 less character
    dec    lastchar
;    Assume ES==DS, direction flag clear
    rep    movsb            ;Move the bytes
    jmp    @cmdedit_25        ;Yes, exit with carry flag set

@cmdedit_15:
    call    near ptr expand_symbol    ;Check if symbol and expand
    jnc    @cmdedit_10        ;If expanded, recurse
    call    near ptr expand_macro    ;Check if line is a macro
;                     and expand if possible.
    jnc    @cmdedit_10        ;If expanded, do recursively.
;                     (note that currently recursion
;                     will take place only on the
;                     last line of a macro definition)
@cmdedit_25:

    mov    user_command,0        ;Init flag
    call    near ptr cmdedit_cmd    ;Check if CMDEDIT command
    jc    @cmdedit_30        ;No
; CMDEDIT command, but might want to return to caller anyway.
    cmp    user_command,1        ;If 1, then return string to caller
    je    @cmdedit_30        ; klugery here for PUSHD/POPD/CHD
;                     to intentionally return a
;                     blank line to DOS in order to
;                     get prompt right.

    jmp    short @cmdedit_3

@cmdedit_30:
; Expand variables if any.
    call    near ptr replace_vars

; Check if line too long for user buffer.
    mov    ax,lastchar        ;AX->last character in buffer
    cmp    ax,linelimit
    jbe    @cmdedit_80        ;We're OK
    mov    ax,E_TRUNCATE        ;error - line too long
    jmp    near ptr abort_processing
@cmdedit_80:
    sub    ax,offset DGROUP:linebuf ;AX<-length of line
; OK now we have a line to give to the caller. Copy it into caller's
; buffer and return.
    pop    di            ;Caller's buffer offset
    pop    es            ;Caller's buffer segment
    inc    di            ;ES:DI->second byte of user buffer
    stosb                ;Store line length
    mov    si,offset DGROUP:linebuf ;SI->Source string
    xchg    cx,ax            ;CX<-length of string
    rep    movsb            ;Copy bytes
    mov    al,CR
    stosb                ;Store terminating carraige-return
; Set cursor shape to caller's shape
    call    near ptr restore_cursor    ;Restore user's cursor shape
    mov    check_break,0        ;Reset flag
    mov    trap_break,0        ; Ctrl-Break handler
    pop    es            ;Restore ES
    ret
cmdedit endp





;+
; FUNCTION : get_next_line
;
;    Gets the next line from the appropriate source and stores it in
;    the line buffer. THe source of the line may be either a macro
;    expansion or a file or the keyboard.
;
; Parameters:
;    None.
;
; Returns:
;    Nothing
; Register(s) destroyed:
;-
get_next_line proc near
    mov    lastchar,offset DGROUP:linebuf
                    ;Empty line (in case not
;                     already done)
    call    near ptr get_macro_line    ;Get next line in expansion
    jnc    @get_next_line_99    ;Jump if there is a next line
                    ;No next line in expansion, so
                    ;get line from keyboard/file
@get_next_line_10:
    call    [source]        ;get_kbd_line / get_file_line
@get_next_line_99:
    ret
get_next_line endp



;+
; FUNCTION : replace_vars
;
;    Replaces all the variables in the current line with their
;    expansions. If the line is too long, aborts with a truncation
;    error.
;
; Parameters:
;    None.
;
; Returns:
;    Nothing.
; Register(s) destroyed:
;    AX,BX,CX,DX
;-
replace_vars proc near
    call    near ptr expand_var        ;CF set if error. AX
;                         contains error code
    jnc    @replace_vars_99
    jmp    near ptr abort_processing    ;Abort processing

@replace_vars_99:
    ret
replace_vars endp



;+
; FUNCTION : get_curpos
;
;    Returns the current cursor position.
;
; Parameters:
;    Global    video_page indicates the page.
;
; Returns:
;    DX    = Current cursor position.
;    CX    = Current cursor scan lines.
; Register(s) destroyed: AX,BX
;-
get_curpos proc    near
    @GetCur    video_page
    ret
get_curpos    endp


;+
; FUNCTION : set_disp_marks
;
;    Sets the marks disp_begin and disp_end to indicate the start
;    and end positions in the line that have been changed. The
;    routine is passed two parameters which indicate
;    the potentially new values for disp_begin and disp_end
;    respectively. However the global disp_begin is changed only if
;    the new value is less than the current value. Similarly
;    disp_end is changed only if the new value is greater than the
;    current value.
;
; Parameters:
;    AX    = potential disp_end
;    DX    = potential disp_begin
;
; Returns:
;    Nothing.
;    May set globals disp_begin and disp_end.
;
; Register(s) destroyed: None.
;-
set_disp_marks    proc near
    cmp    ax,disp_end        ;New value greater ?
    jb    @set_disp_marks_10    ;No
    mov    disp_end,ax        ;New disp_end
@set_disp_marks_10:
    cmp    dx,disp_begin        ;New value smaller
    jnb    @set_disp_marks_20    ;No
    mov    disp_begin,dx        ;New disp_begin
@set_disp_marks_20:
    ret
set_disp_marks    endp


;+
; FUNCTION : disp_line
;
;    Displays the current contents of the line buffer. Since the
;    entire line is not redisplayed everytime, all procedures that
;    change the contents of the line buffer have to follow certain
;    rules in order to make sure the display correctly shows the
;    line. The variable disp_begin must be set to the earliest
;    position in the line that has been changed and disp_end to beyond
;    last position in the line that has been changed.;
; Parameters:
;    None.
;
; Returns:
;    Nothing
; Register(s) destroyed:
;-
disp_line proc near
    @save    si,di
    mov    ax,disp_begin        ;Lower limit of changed chars
    mov    si,ax
    mov    cx,disp_end        ;CX->byte after last char that
;                     has changed
    sub    cx,si            ;CX<-num chars to be output
    jcxz    @disp_line_90        ;Nothing to be updated
    push    cx            ;Save CX across calls
    call    near ptr line_to_scr    ;Move cursor to corresponding
;                     position on the screen.
;    OK, now we are ready to begin updating the screen.
    call    near ptr get_curpos    ;DX<-current cursor position
    pop    cx            ;Restore CX
    mov    di,lastchar        ;DI->beyond last char
    cmp    si,di            ;Beyond last char?
    je    @disp_line_25        ;Go display blanks
@disp_line_10:                ;Loop to output chars
    lodsb                ;AL<-next char
    @DispCh    al            ;Display it
    push    cx            ;Save CX
    push    dx            ;Save old cursor position
    call    near ptr get_curpos    ;DX<-new cursor position
                    ; BX destroyed
    pop    bx            ;BX<-old cursor position
    pop    cx            ;Restore CX
    or    dl,dl            ;Column 0 ?
    jne    @disp_line_20        ;Nope
                    ;Col 0
    cmp    bh,dh            ;Is the row the same
    jne    @disp_line_20
                    ;yes, screen scrolled
    dec    initial_curpos+1    ;Decrement the row for initial
;                     cursor position
@disp_line_20:
    mov    bx,dx            ;New cursor position
    cmp    si,di            ;Beyond last char?
    loopne    @disp_line_10        ;Keep looping until count exhausted or
;                     beyond last char
@disp_line_25:
;    Now all changed positions have been displayed. If CX is not 0,
;    then the remaining char positions have to be
;    replaced with blanks. Note that since we are now overwriting
;    previously displayed positions, no need to check for line
;    wraparound or scroll.

    jcxz    @disp_line_90        ;No more chars

    mov    al,' '            ;Overwrite with blanks
@disp_line_30:
    @DispCh    al
    loop    @disp_line_30
@disp_line_90:
    mov    ax,dot
    mov    disp_begin,ax        ;Initialize for next call
    mov    disp_end,ax
    call    near ptr line_to_scr    ;Set cursor at dot

    @restore
    ret
disp_line endp





;+
; FUNCTION : line_to_scr
;
;    Places the cursor at the screen position corresponding to a
;    specific position in the line buffer. The entire line buffer
;    upto that position must have been displayed before.
;
; Parameters:
;    AX    = Pointer into the line buffer
;
; Returns:
;    Nothing.
; Register(s) destroyed: AX, BX, DX
;-
line_to_scr proc near
    sub    ax,offset dgroup:linebuf ;ax<-num chars
    mov    dx,initial_curpos    ;Initial cursor position
;                     dh<-row, dl<-column
    xor    bh,bh
    mov    bl,dl            ;BX<-original column
    add    ax,bx            ;Compensate for initial position.
;                     AX is now the 'virtual column'
    mov    bl,screen_width        ;BX<-width of screen
@line_to_scr_10:            ;Loop to skip over chars that
;                     do not need to be updated
    cmp    ax,bx            ;Num of chars fit on a line?
    jb    @line_to_scr_20        ;Yes, exit loop
    sub    ax,bx            ;Go to next line
    inc    dh            ;Increment the row
    jmp    short @line_to_scr_10
@line_to_scr_20:
; al now contains the column and dh the row where the cursor should
; be placed
    mov    dl,al            ;dx<-screen position
    @SetCurPos ,,video_page        ;Set the cursor position
    ret
line_to_scr endp




;+
; FUNCTION : insert_chars
;
;    Inserts a string of chars at the specified position in the
;    linebuffer. If the length would exceed the size of the line buffer,
;    chars are only store until the buffer is full and the carry flag is
;    set. Dot is updated appropriately.
;
; Parameters :
;
;    SI    - ptr to source string
;    DI    - ptr to insert position. This must lie in the line buffer.
;    AX    - length of source string
;
; Returns:
;    CF    = 1 if could not be fitted into linebuf
;          0 otherwise
;
; Registers destroyed:
;    AX,CX,DX
insert_chars proc near
    @save    si,di
    mov    dx,di            ;Save insert position in DX
    mov    di,lastchar        ;First empty position
    mov    cx,offset DGROUP:linebuf_suffix
    sub    cx,di            ;Subtract current last position
;                     CX<-max chars that will fit
    cmp    cx,ax            ;Will all chars fit ?
    jb    @insert_chars_5    ;Not all chars will fit
    xchg    ax,cx            ;All chars will fit
@insert_chars_5:
;    CX is number of chars to insert
    pushf                ;Remember CF
;    Make place for the characters to be inserted by moving current
;    characters up by CX.
    mov    ax,di
    sub    ax,dx            ;AX<-num chars to move
    push    si            ;Remember source address
    mov    si,di            ;SI->first char to be moved
    add    di,cx            ;DI -> new value of lastchar
    mov    lastchar,di        ;Store it
    xchg    ax,cx            ;AX<-num chars to insert
;                     CX<-num chars to move
    std                ;Direction is downward
    cmpsb                ;Decrement SI,DI
    rep    movsb            ;Make place
    cld
    pop    si            ;Restore string source
; Before inserting the chars, update the dot if it is affected.
    cmp    dx,dot            ;Is the dot at or after the insert
;                     position ?
    jb    @insert_chars_50    ;No, jump
    add    dot,ax            ;Else update the dot
@insert_chars_50:
    mov    di,dx            ;DI->insert position
    xchg    cx,ax            ;CX<-num chars to insert
    rep    movsb            ;Copy string into linebuffer
    mov    ax,lastchar
    call    near ptr set_disp_marks    ;AX,DX are parameters
    popf                ;Restore CF

    @restore
    ret
insert_chars endp


;+
; FUNCTION : insert_at_dot
;
;    Inserts a string of characters into the line buffer in the
;    position pointed to by dot. If the length specified in global
;    caller_buflen will be exceeded,chars are only stored until the
;    buffer is full and CF is set.
;
; Parameters:
;    SI    = ptr to source string
;    AL    = length of string
;
; Returns:
;    CF    = 1 if could not be fitted into linebuf
;          0 otherwise
; Register(s) destroyed:
;    <TBA>
;-
insert_at_dot proc near
    @save    si,di,dx
    xor    ah,ah            ;AX<-length of source string
    mov    di,dot            ;DI-> insert position
    call    near ptr insert_chars    ;Params SI,DI,AX, returns status in CF
    @restore
    ret
insert_at_dot endp




;+
; FUNCTION : remove_chars
;
;    Removes a string of chars at the specified position in the
;    linebuffer. The display markers and the lastchar global are updated
;    accordingly.
;
; Parameters :
;
;    SI    - ptr to position in linebuf from which to delete
;    AX    - number of chars to delete.
;
; Returns:
;    Nothing.
;
; Registers destroyed:
;    AX,CX,DX
remove_chars proc near
    @save    si,di
    mov    di,ax            ;Save delete count

; First update the display markers
    mov    ax,lastchar
    mov    dx,si
    call    near ptr set_disp_marks    ;AX,DX params
    mov    ax,lastchar
    sub    ax,si            ;Num chars after delete position
    cmp    ax,di            ;More than the specified number ?
    jb    @remove_chars_10    ;No, so just delete that many bytes
    mov    ax,di
@remove_chars_10:
; AX is number of bytes to delete. See if the dot needs to be updated.
    mov    di,si            ;DI->delete position
    add    si,ax            ;SI->first char after delete string
    cmp    di,dot
    jnb    @remove_chars_40    ;dot before delete pos, so
;                     unaffected
    cmp    si,dot            ;Is dot beyond it delete range
    jb    @remove_chars_30    ;Yes
; dot is in delete region. Update it to point to first delete position
    mov    dot,di
    jmp    short @remove_chars_40
@remove_chars_30:
; dot is beyond delete position. So subtract delete bytes from it.
    sub    dot,ax

@remove_chars_40:
; Now that the screen markers and dot have been updated, get down to the
; real business at hand. SI points to first char after delete string, DI is
; the delete position. AX is number of bytes to be deleted.
    mov    cx,lastchar
    sub    lastchar,ax        ;Update lastchar
    sub    cx,si            ;CX<-num bytes to move
    rep    movsb            ;Move 'em
; All done

    @restore
    ret
remove_chars endp


;+
; FUNCTION : erase_to_dot
;
;    Deletes all characters from the line buffer between the
;    positions AX and dot. (Either AX or dot may be specify the
;    beginning of range to be deleted). The markers disp_begin and
;    disp_end are set to reflect the changed positions in the line.
;    Global lastchar is also updated.
; Parameters:
;    AX    = One endpoint of the range to be deleted.
;    Global    dot is the other.
; Returns:
;    Nothing.
; Register(s) destroyed:
;-
erase_to_dot proc near
    @save    si
    mov    si,dot
    cmp    ax,si            ;Make sure AX is after dot
    jnb    @erase_to_dot_10    ;Yes it is
    xchg    si,ax            ;Else exchange
@erase_to_dot_10:            ;AX is low end, SI high end
    sub    ax,si            ;AX is num bytes to delete
    call    near ptr remove_chars    ;Delete AX chars starting at [SI]
    @restore
    ret
erase_to_dot endp


;+
; FUNCTION : cmdedit_cmd
;
;    Checks if the line buffer contains a CMDEDIT command and if so
;    executes it.
;
; Parameters:
;    None.
;
; Returns:
;    CF    = 0 if the line was a command
;          1 otherwise.
; Register(s) destroyed:
;    AX,BX,CX,DX
;-
cmdedit_cmd proc near
    @save    si,di
    mov    si,offset DGROUP:linebuf    ;SI->linebuf
    mov    di,lastchar            ;DI->end of line in linebuf
; Skip leading whitespace
    mov    cx,di
    sub    cx,si                ;CX<-num chars in linebuf
    call    near ptr skip_whitespace    ;SI->first non-whitespace char
;                         CX<-num remaining chars
    jcxz    @cmdedit_cmd_99            ;No command on line
    mov    di,si                ;DI->first char of word
; Skip first word (name of this command)
    call    near ptr skip_nonwhite        ;SI->first whitespace after
;                             command name
;                         CX<-num remaining chars
    mov    ax,si
    sub    ax,di                ;AX<-num chars in word
    cmp    ax,MAX_CMD_LEN            ;Word too long to be command?
    ja    @cmdedit_cmd_98            ;Yes, exit
; Now search thru the command table to see if the first word in the line is a
; CMDEDIT command. Currently, DI->start of word, AX = num chars in word
    xor    dx,dx                ;DX<-Command number
    mov    si,offset dgroup:cmd_table    ;SI->Start of commands

@cmdedit_cmd_10:
    xor    ch,ch                ;Clear high bits
    mov    cl,[si]                ;CX<-Length of command
    jcxz    @cmdedit_cmd_98            ;End of table, exit
    inc    si                ;SI->command
    cmp    cx,ax                ;Lengths match
    jne    @cmdedit_cmd_30            ;No, go try next command
    xchg    bx,ax                ;BX<-num chars in word
    call    near ptr stre_cmp        ;Compare strings
    xchg    ax,bx                ;AX<-num chars in word
    je    @cmdedit_cmd_50            ;Command matched

@cmdedit_cmd_30:
    xor    ch,ch
    mov    cl,-1[si]            ;AX<-length of command
    add    si,cx                ;SI->length of next command
    inc    dx                ;Increment the command number
    jmp    short @cmdedit_cmd_10        ;Try next command

@cmdedit_cmd_50:                ;Found command
    mov    si,di                ;SI->first char of command
    add    si,ax                ;SI->first char after command
    mov    cx,lastchar
    sub    cx,si                ;CX<-num chars after command
    mov    di,dx                ;BX<-command number
    shl    di,1                ;BX<-offset into table
    call    cmd_func_table[di]        ;Execute it
;                         Params:
;                         SI->first char after command
;                         CX = remaining length of line
;                         (after command)
    cmp    source,offset DGROUP:get_kbd_line
    jne    @cmdedit_cmd_60
    call    near ptr disp_prompt        ;Display user prompt
@cmdedit_cmd_60:
    clc                    ;CF = 0
    jmp    short @cmdedit_cmd_99
@cmdedit_cmd_98:                ;No command found
    stc                    ;CF = 1
@cmdedit_cmd_99:
    @restore
    ret
cmdedit_cmd endp




;+
; FUNCTION : abort_processing
;
;    Called by various routines in case of any errors that require
;    aborting of any ongoing processing. An error message is
;    displayed and CMDEDIT state is reset to accept input from the
;    keyboard. The routine adjusts the stack pointer to a previously
;    stored state. Execution then continues at a `abort entry'
;    point. The routine does NOT return to the caller.
;
; Parameters:
;    AX    = Error message number.
;
; Returns:
;    Does NOT return to caller.
;
; Register(s) destroyed:
;    Potentially all but irrelevant since routine does not return to
;    caller.
;-
abort_processing proc near
    mov    macro_level,0            ;Reset macro level
    mov    source,offset DGROUP:get_kbd_line ;Set input to keyboard

; Display a message
    mov    si,offset DGROUP:abort_msg_hd
    mov    di,offset DGROUP:linebuf
    mov    dot,di                ;dot MUST be at
;                         beginning of line
;                         since this position is
;                         stored in the main routine
    mov    cx,ABORT_HDR_LEN
    rep    movsb                ;Copy message header
    sal    ax,1
    sal    ax,1                ;AX is now index into msg table
    xchg    ax,bx
    mov    si,abort_msg_ptrs[bx]        ;SI->message
    mov    cx,abort_msg_ptrs[bx+2]        ;CX<-length of message
    rep    movsb                ;Copy msg into linebuf
    mov    si,offset DGROUP:abort_msg_tl
    mov    cx,ABORT_TAIL_LEN
    rep    movsb                ;Copy tail of message
    mov    lastchar,di
    mov    ax,di                ;Set display marks
    mov    dx,offset DGROUP:linebuf
    call    near ptr set_disp_marks
    call    disp_line            ;Display message
    call    near ptr restore_cursor        ;Restore cursor to user shape
    @DispCh    CR
    @DispCh    LF
    call    near ptr disp_prompt
    mov    sp,abort_entry_stack
    jmp    near ptr cmdedit_abort_entry

abort_processing endp



;+
; FUNCTION : restore_cursor
;
;    Restores the cursor to the user's shape.
;
; Parameters:
;    Global caller_cursor contains original shape
;
; Returns:
;
; Register(s) destroyed:
;    None.
;-
restore_cursor    proc near
    @save    ax,cx
    mov    cx,caller_cursor
    IF    TOGGLE_CURSOR
    @SetCurSz ch,cl
    ENDIF
    @restore
    ret
restore_cursor    endp


;+
; FUNCTION : reset_line
;
;    Called to init various things like cursor shape, history buffer
;    character positions etc.
;
; Parameters:
;    None.
;
; Returns:
;    Nothing.
;
; Register(s) destroyed:
;    AX,BX,CX,DX
;-
reset_line proc near
    call    near ptr hist_top    ;Reset history stack ptr to top
    call    near ptr restore_cursor    ;Reset cursor shape
    mov    ax,offset dgroup:linebuf
    mov    lastchar,ax        ;End of line
    mov    dot,ax            ;current pos in line
    mov    disp_begin,ax        ;first pos that changed
    mov    disp_end,ax        ;last pos that changed

; Init overstrike/insert mode
    mov    bl,default_imode    ;Default edit mode
;                     (insert/overstrike)
    mov    edit_mode,bl        ;Init insert/overtype mode

; Initialize the cursor shapes for insert and overstrike mode
    mov    ax,caller_cursor    ;Caller's cursor shape
    IF    TOGGLE_CURSOR
    mov    ah,al
    sub    ah,3
    mov    imode_cursor,ax        ;Insert mode cursor
    mov    ah,al
    sub    ah,1
    mov    omode_cursor,ax        ;Overtype mode cursor

; Init cursor shape
    xor    bh,bh
    add    bx,bx
    mov    cx,omode_cursor[bx]
    mov    ah,01h
    int    10h

    ELSE

    mov    omode_cursor,ax
    mov    imode_cursor,ax

    ENDIF

    mov    bh,video_page
    @GetCur bh
    mov    initial_curpos,dx    ;Initial cursor position

    ret
reset_line endp


;+
; FUNCTION : init_screen
;
;    Inits various screen parameters. Reads the current prompt from
;    the screen and store in the prompt buffer. prompt buffer is
;    assumed to be at most the width of the screen.
;
; Parameters:
;    None.
;
; Returns:
;    Nothing.
; Register(s) destroyed:
;    AX,BX,CX,DX
;-
init_screen proc near
    @save    si,di
    @GetMode            ;Get the video mode
    mov    video_page,bh        ;Store page
    mov    screen_width,ah        ; and width of display

    @GetCur    bh            ;Get the cursor shape and position
    mov    initial_curpos,dx    ;Initial cursor position
    mov    caller_cursor,cx    ;Caller's cursor shape

    mov    di,offset DGROUP:prompt
    mov    cx,PROMPT_BUF_SIZE    ;CX<-size of prompt buffer
;                     (assumed not 0)
    mov    si,dx            ;DX<-cursor pos
    xor    dl,dl            ;DX<-position at start of row

@init_screen_5:
; BH holds video page, DX is cursor position, SI is ending cursor
; position, CX is remaining space in prompt buffer
    @SetCurPos    ,,bh        ;Set cursor position
    cmp    dx,si            ;Reached original position ?
    je    @init_screen_10        ;Yes, all done
    @GetChAtr    bh        ;Get char at cursor
    stosb                ;Store in prompt buffer
    inc    dl            ;Increment cursor position
    loop    @init_screen_5        ;loop unless prompt buffer full
@init_screen_10:
    sub    di,offset DGROUP:prompt
    mov    prompt_length,di    ;Store length of prompt

    @restore
    ret
init_screen endp



;+
; FUNCTION : disp_prompt
;
;    Called to display the user's prompt. The prompt is taken from
;    the buffer 'prompt'.
;
; Parameters:
;    None.
;
; Returns:
;    Nothing.
; Register(s) destroyed:
;    <TBA>
;-
disp_prompt    proc near
    @save    si
    @DispCh    CR
    @DispCh LF
    mov    cx,prompt_length
    jcxz    @disp_prompt_99
    mov    si,offset DGROUP:prompt
@disp_prompt_10:
    lodsb
    @DispCh    al
    loop    @disp_prompt_10
@disp_prompt_99:
    @restore
    ret
disp_prompt    endp




;+
; FUNCTION : makeroom
;
;    Called to push a specified number of characters from the end of a
;    line to the back of the line buffer.
;
; Parameters:
;    CX    - number of chars to push back
;
; Returns:
;    DI    - points to the first char of the string pushed back.
; Register(s) destroyed:
;    CX
;-
makeroom proc near
    @save    si
    mov    si,lastchar        ;end of line
    dec    si
    mov    di,offset DGROUP:linebuf_suffix ;Di->end of linebuf (we
;                         want to move chars in
;                         reverse order)
    std
    rep    movsb            ;Move up characters
    cld
    inc    di            ;DI->start of string
    @restore
    ret
makeroom endp


;+
; FUNCTION : getpsp
;
;    Returns the PSP of the current process
;
; Returns:
;    BX - segment of current PSP
;
; Registers destroyed :
;    AX,BX
;-
getpsp proc near
; Get the PSP of the current process
    cmp    dos_version_major,2
    jbe    @getpsp_10
;    DOS 3.x or above - use documented call
    mov    ah,62h
    jmp    short @getpsp_90
@getpsp_10:
; DOS version 2.x - use undocumented call
    mov    ah,51h
@getpsp_90:
    int    21h                ;BX->PSP segment
    ret
getpsp endp



;+
; Function : locate_dosenv
;
;    Locates the segment in which the current environment is located.
;    This environment is the 'current' environment which may not
;    necessarily be the root environment.
;
; Parameters:
;    None.
;
; Returns:
;    AX    - segment of environment
;
; Register(s) destroyed:
;    AX
;-
locate_dosenv proc near
    @save    bx,si,es

    call    near ptr getpsp            ;BX->segment of psp
    mov    es,bx                ;ES->segment of psp

;    Loop to find the current command.com psp
    mov    si,16h                ;ES:SI->parent psp
    xor    ax,ax                ;Init for loop
    jmp    short @locate_dosenv_20        ;'while' loop

@locate_dosenv_10:
    mov    ax,es:[si]            ;AX<-psp seg
    mov    es,ax                ;ES->psp of parent
@locate_dosenv_20:
    cmp    ax,es:[si]            ;Is psp == parent psp ?
    jne    @locate_dosenv_10

; ES contains DOS PSP.
    mov    ax,es:[2ch]            ;Offset 2c is env address

; AX->DOS environment
;    mov    dos_envseg,ax
    cmp    dos_version_major,2        ;DOS 2.x ?
    je    @locate_dosenv_50
; Versions 3.x or higher
    cmp    dos_version_minor,10        ;3.1 or below ?
    jle    @locate_dosenv_50        ;If so handle like 2.x
    cmp    dos_version_minor,30        ;3,3 or above ?
    jge    @locate_dosenv_99        ;Then all done
; DOS version higher than 3.1 but below 3.3.
    jmp    short @locate_dosenv_60


@locate_dosenv_50:
; DOS version 2.x-3.1. If the environement is non-0, all done. Else the
; environment is the memory block below the command.com.
    or    ax,ax                ;0 ?
    jne    @locate_dosenv_99        ;No, all done
@locate_dosenv_60:
    mov    si,es
    dec    si                ;SI is segment of memory
;                         control block of command.com
    mov    es,si
    mov    ax,es:[3]            ;AX->size of command.com in
;                         paragraphs
    inc    ax                ;Add size of MCB to AX (in
;                         paras)
    add    ax,si                ;AX->MCB of environment
    inc    ax                ;AX->environment
;    mov    dos_envseg,ax            ;Store it.

@locate_dosenv_99:
; OK, now dos_envseg supposedly contains the environment segment. DO some
; heuristics to make sure it is really what we think it is.


    @restore
    ret
locate_dosenv endp



;+
; FUNCTION : our_break_handler
;
;    This takes over the Ctrl-Break interrupt and sets a flag when
;    Ctrl-Break is hit. It then jumps to the original Ctrl-Break handler.
;
; Parameters:
;
;
; Returns:
;
; Register(s) destroyed:
;-
our_break_handler proc near
    inc    CS:check_break
    cmp    CS:trap_break,1
    jne    @our_break_handler_10
    iret
@our_break_handler_10:
    jmp    CS:prev_isr1b
our_break_handler endp

CSEG    ENDS

    END    entry