Simtel MSDOS 1993 May/SIMTEL_0593.ISO/msdos/c/unixclib.asm

Assembly Source File | 1985-10-14 | 10.0 KB | 330 lines

    title    UNIXCLIB - UNIX/C FUNCTIONS FOR PC/MS-DOS
    page    55,131

; UNIXCLIB - Routines for providing UNIX-like functions for PC/MS-DOS
;
; Date of last update: 10/9/85
;
; This is a package of routines that
;
;    (1) emulate routines found in the standard C function libraries on
;        UNIX systems, and/or
;    (2) help bridge the gap between MS-DOS and Unix.
;
;
; Author credit summary:
;
;    Function        Author            Organization
;
;    sleep            Lawrence B. Afrin    Clemson University
;    file_exists            "            "
;    set_jmp                "            "
;    long_jmp            "            "
;
;
; This package was conceived by Lawrence B. Afrin of Clemson University.
; Please send all questions, comments, suggestions, and new routines to
; LBAFRIN@CLEMSON (CSNet) or LBAFRIN.CLEMSON@CSNET-RELAY (ARPANet).  These
; routines were principally written for support of DeSmet C, although
; they can probably be easily interfaced to any C compiler if you know
; the compiler's mechanism(s) or protocol(s) for calling assembler
; routines.
;
; The current catalog of routines in UNIXCLIB.ASM follows:
;
;    sleep(x)        functionally equivalent to UNIX sleep(3) -
;        int x        pauses execution for x seconds
;
;    file_exists(s)        determines whether the named PC/MS-DOS file
;        char *s        exists - helps in building support for the
;                UNIX System V O_CREAT feature (create/open
;                file only if it doesn't already exist)
;
;    long_jmp(j)        major enhancement to DeSmet longjmp() -
;        jmp_buf j;    provides functionality identical to the
;                standard UNIX longjmp() (which DeSmet doesn't)
;
;    set_jmp(j)        major enhancement to DeSmet setjmp() -
;        jmp_buf j;    provides functionality identical to the
;                standard UNIX setjmp() (which DeSmet doesn't)
;
;
; Remember, send your contributions to this library to LBAFRIN@CLEMSON.
; I'm happy to receive DeSmet-related and non-DeSmet-related routines for
; review.  I can usually respond to submissions within a day or two, but
; please don't complain if you see my response time lagging.  As a
; medical student I have to put my academic and patient responsibilities
; at a higher priority than the public service of supervising this library.
;
;                        -- Larry Afrin
;                           Dept. of Computer Science
;                           Clemson University



; Implementation notes for the following 4 routines:  All were tested under
; MASM v1.00, DeSmet C 2.41, and PC-DOS 3.10.  Most versions of MASM and
; DeSmet C should work.  I expect that PC/MS-DOS 2.x and 3.0 work fine,
; too, but I don't think 1.10 will hack it.

;
; DeSmet puts all code segments in the `pgroup' group and all data segments
; in the `dgroup' group.
;
pgroup    group    prog
dgroup    group    data

prog    segment    para public 'prog'
    assume    cs:prog,ds:data,es:nothing

    public    sleep
    public    file_exists
    public    set_jmp
    public    long_jmp

;
; sleep - written by Lawrence B. Afrin of Clemson University
; (lbafrin@clemson).  Provides UNIX-like sleep(3) functionality.
;
;    calling mechanism is:    push    <number of seconds to sleep>
;                call    sleep
;
;    note that this limits the maximum sleep time to 65535 seconds
sleep    proc    near
    push    bp            ; enter in a DeSmet-approved (more or
    mov    bp,sp            ;   less) manner
    sub    sp,10
    push    ax            ; save regs
    push    bx
    push    cx
    push    dx
    cmp    ax,0            ; test for sleep(x) where x <= 0
    jg    sleep8
    jmp    sleep7            ; ignore call if such is the case
sleep8:    mov    ah,2ch            ; get the current time from DOS
    int    21h
    mov    [bp-2],cx        ; [bp-4:bp-2] hold the original time
    mov    [bp-4],dx
    mov    [bp-6],cx        ; [bp-8:bp-6] will hold the target
    mov    [bp-8],dx        ;   time (when we end our sleep)
    mov    word ptr [bp-10],60
    mov    ax,[bp+4]
    xor    dx,dx
    div    word ptr [bp-10]
    add    dl,[bp-7]        ; add num of secs (mod 60) to orig secs
    cmp    dl,60
    jl    sleep0
    sub    dl,60            ; overflow of targ secs, so take mod 60
    inc    byte ptr [bp-6]        ;   and increment target minutes
sleep0:    mov    [bp-7],dl
    cmp    ax,0
    je    sleep3
    xor    dx,dx
    div    word ptr [bp-10]
    add    dl,[bp-6]        ; add num of mins (mod 60) to targ mins
    cmp    dl,60
    jl    sleep1
    sub    dl,60            ; overflow of targ mins, so take mod 60
    inc    byte ptr [bp-5]        ;   and increment target hours
sleep1:    mov    [bp-6],dl
    cmp    ax,0
    je    sleep3
    add    al,[bp-5]
    cmp    al,24
    jl    sleep2
    sub    al,24
sleep2:    mov    [bp-5],al        ; by now we know our target time
                    ; now let's start looping until we hit
                    ;   the target time
sleep3:    mov    ah,2ch            ; top of loop: get current time
    int    21h
    mov    ax,[bp-6]
    mov    bx,[bp-8]
    cmp    cx,[bp-2]    ; if current time >= original time (don't have
    jg    sleep4        ;   to worry about 24 hour wraparound because
    jl    sleep6        ;   max number of sleep secs = 65535, which
    cmp    dx,[bp-4]    ;   is < 24 hours (= 86400))
    jl    sleep6
sleep4:    cmp    ax,[bp-2]    ;   then if target time <= original time
    jg    sleep5
    jl    sleep3
    cmp    bx,[bp-4]
    jle    sleep3        ;          then loop again
sleep5:    cmp    cx,ax        ;          else if current time >= target time
    jg    sleep7        ;                 then exit
    jl    sleep3        ;                 else loop again
    cmp    dx,bx
    jl    sleep3
    jmp    sleep7
sleep6:    cmp    ax,[bp-2]    ;   else if target time > original time
    jg    sleep7
    cmp    bx,[bp-4]
    jg    sleep7        ;          then exit
    cmp    cx,ax        ;          else if current time >= target time
    jg    sleep7        ;                 then exit
    jl    sleep3        ;                 else loop again
    cmp    dx,bx
    jl    sleep3
sleep7:    pop    dx        ; exit
    pop    cx
    pop    bx
    pop    ax
    mov    sp,bp
    pop    bp
    ret
sleep    endp


;
; file_exists - written by Lawrence B. Afrin of Clemson University
; (lbafrin@clemson).  Tells caller whether specified PC/MS-DOS file
; already exists.  Helpful in building higher level file system support
; such as for the O_CREAT flag in the UNIX System V open(2) call.
;
;    calling mechanism is:    push    <address (in data seg) of filename string>
;                call    file_exists
;
;    returns AX = 0 if file does not exist
;        AX = 1 if file does exist
;
; Note that file_exists temporarily establishes a new Disk Transfer Address.
;

data    segment    para public 'data'

file_exists_dta    db    128 dup (?)
old_dta_seg    dw    ?
old_dta_off    dw    ?

data    ends

file_exists    proc    near
    push    bp            ; play DeSmet games
    mov    bp,sp
    push    bx
    push    cx
    push    dx
    push    es
    mov    ah,2fh            ; get old dta
    int    21h
    mov    old_dta_seg,es        ; save old dta
    mov    old_dta_off,bx
    mov    dx,offset dgroup:file_exists_dta
    mov    ah,1ah
    int    21h            ; set up temp dta
    mov    dx,[bp+4]
    mov    ah,4eh
    mov    cx,0
    int    21h            ; ask DOS if file exists
    mov    cx,1            ; assume it does
    cmp    ax,0            ; does it?
    je    file_exists_x        ; yup
    mov    cx,0            ; whoops, no it doesn't
file_exists_x:
    push    cx            ; save return code
    push    ds
    mov    dx,old_dta_off
    mov    ax,old_dta_seg
    mov    ds,ax
    mov    ah,1ah
    int    21h            ; restore old dta
    pop    ds
    pop    ax            ; restore return code
    pop    es
    pop    dx
    pop    cx
    pop    bx
    mov    sp,bp
    pop    bp
    ret
file_exists    endp


; set_jmp and long_jmp - written by Lawrence B. Afrin of Clemson University
; (lbafrin@clemson).  Provides UNIX-like setjmp(3) and longjmp(3) function-
; ality, significantly extends functionality of DeSmet counterparts.
;
; Note that the type of the "jmp_buf"-type variable in this implementation
; is a three-element one-dimensional integer array.  (The C statement would be
; "typedef int jmp_buf[3];".
;
; set_jmp:
;    calling mechanism is:    push    <address (in data seg) of jmp_buf var>
;                call    set_jmp
;
;    returns AX = 0
;
; long_jmp:
;    calling mechanism is:    push    <value to be faked as set_jmp return val>
;                push    <address (in data seg) of jmp_buf var>
;                call    long_jmp
;
;    causes a return with AX = "fake return val" to the instruction follow-
;    ing the call to set_jmp that was made specifying the same jmp_buf
;    variable
;
; IMPORTANT NOTES!!!
;
;    (1) These routines are specific for DeSmet C and probably no other C
;        compilers.  They depend heavily on the DeSmet protocol used
;        to manage stack frames.
;    (2) The same warnings as in the DeSmet manual apply here.  A long_jmp
;        into a routine containing the corresponding set_jmp, when the
;        target routine is no longer "active" (i.e., on the stack), has
;        a totally unguaranteed result.
;    (3) The performance of these routines under the DeSmet debugger has
;        not been tested.  Use at your own risk!
;
;
; How It Works
;
;    The DeSmet "environment" that needs to be saved and restored by
;    set_jmp/long_jmp consists of an address to jump/return to, the
;    current frame pointer (found in BP), and the current stack
;    pointer (you guessed it, SP).  set_jmp saves these values into
;    the jmp_buf, and long_jmp restores SP and BP and then plays a
;    trick so that when it returns, it actually is as if the
;    corresponding set_jmp were returning (except that the return value
;    is as specified in the call to long_jmp).
;

set_jmp    proc    near
    push    bp        ; we're going to do this without disturbing
    push    bx        ;   regs except the return value reg, AX
    mov    bp,sp        ; let's get some addressability here
    mov    bx,[bp+6]    ; load the jmp_buf address into BX
    mov    ax,[bp+4]    ; load the target jump address into AX
    mov    [bx],ax        ; tuck this address away in (int) jmp_buf[0]
    lea    ax,[bp+6]    ; load into AX the value that we're going to
                ;   want to give SP in the long_jmp
    mov    [bx+2],ax    ; tuck that away in (int) jmp_buf[1]
    mov    ax,[bp+2]    ; load into AX the BP (frame ptr) we saved above
    mov    [bx+4],ax    ; save that, too, in (int) jmp_buf[2]
    pop    bx        ; that's it!  now restore regs,
    pop    bp
    mov    ax,0        ; set the return code
    ret            ; and get out of here
set_jmp    endp

long_jmp    proc    near    ; notice that we get away with this without
                ;   having to play with any registers not
                ;   intimately involved in the concept of
                ;   a long_jmp; neat, huh?
    mov    bp,sp        ; use bp for work variable
    mov    ax,[bp+4]    ; load long_jmp's 2nd argument as the return val
    mov    bp,[bp+2]    ; now point bp at the jmp_buf
    mov    sp,ds:[bp+2]    ; load SP
    push    ds:[bp+0]    ; push the target address onto the `new' stack
    mov    bp,ds:[bp+4]    ; load BP
                ; (The stack should now be looking *exactly*
                ; as if it's ready for a NEAR-type return
                ; from the corresponding set_jmp call, except
                ; that AX has the return value specified in
                ; the long_jmp call.)
    ret            ; let's get back to work
long_jmp    endp

prog    ends

    end