;

; jmemdosa.asm

;

; Copyright (C) 1992, Thomas G. Lane.

; This file is part of the Independent JPEG Group's software.

; For conditions of distribution and use, see the accompanying README file.

;

; This file contains low-level interface routines to support the MS-DOS

; backing store manager (jmemdos.c). Routines are provided to access disk

; files through direct DOS calls, and to access XMS and EMS drivers.

;

; This file should assemble with Microsoft's MASM or any compatible

; assembler (including Borland's Turbo Assembler). If you haven't got

; a compatible assembler, better fall back to jmemansi.c or jmemname.c.

;

; To minimize dependence on the C compiler's register usage conventions,

; we save and restore all 8086 registers, even though most compilers only

; require SI,DI,DS to be preserved. Also, we use only 16-bit-wide return

; values, which everybody returns in AX.

;

; Based on code contributed by Ge' Weijers.

;

JMEMDOSA_TXT segment byte public 'CODE'

assume cs:JMEMDOSA_TXT

public _jdos_open

public _jdos_close

public _jdos_seek

public _jdos_read

public _jdos_write

public _jxms_getdriver

public _jxms_calldriver

public _jems_available

public _jems_calldriver

;

; short far jdos_open (short far * handle, char far * filename)

;

; Create and open a temporary file

;

_jdos_open proc far

push bp ; linkage

mov bp,sp

push si ; save all registers for safety

push di

push bx

push cx

push dx

push es

push ds

mov cx,0 ; normal file attributes

lds dx,dword ptr [bp+10] ; get filename pointer

mov ah,3ch ; create file

int 21h

jc open_err ; if failed, return error code

lds bx,dword ptr [bp+6] ; get handle pointer

mov word ptr [bx],ax ; save the handle

xor ax,ax ; return zero for OK

open_err: pop ds ; restore registers and exit

pop es

pop dx

pop cx

pop bx

pop di

pop si

pop bp

ret

_jdos_open endp

;

; short far jdos_close (short handle)

;

; Close the file handle

;

_jdos_close proc far

push bp ; linkage

mov bp,sp

push si ; save all registers for safety

push di

push bx

push cx

push dx

push es

push ds

mov bx,word ptr [bp+6] ; file handle

mov ah,3eh ; close file

int 21h

jc close_err ; if failed, return error code

xor ax,ax ; return zero for OK

close_err: pop ds ; restore registers and exit

pop es

pop dx

pop cx

pop bx

pop di

pop si

pop bp

ret

_jdos_close endp

;

; short far jdos_seek (short handle, long offset)

;

; Set file position

;

_jdos_seek proc far

push bp ; linkage

mov bp,sp

push si ; save all registers for safety

push di

push bx

push cx

push dx

push es

push ds

mov bx,word ptr [bp+6] ; file handle

mov dx,word ptr [bp+8] ; LS offset

mov cx,word ptr [bp+10] ; MS offset

mov ax,4200h ; absolute seek

int 21h

jc seek_err ; if failed, return error code

xor ax,ax ; return zero for OK

seek_err: pop ds ; restore registers and exit

pop es

pop dx

pop cx

pop bx

pop di

pop si

pop bp

ret

_jdos_seek endp

;

; short far jdos_read (short handle, void far * buffer, unsigned short count)

;

; Read from file

;

_jdos_read proc far

push bp ; linkage

mov bp,sp

push si ; save all registers for safety

push di

push bx

push cx

push dx

push es

push ds

mov bx,word ptr [bp+6] ; file handle

lds dx,dword ptr [bp+8] ; buffer address

mov cx,word ptr [bp+12] ; number of bytes

mov ah,3fh ; read file

int 21h

jc read_err ; if failed, return error code

cmp ax,word ptr [bp+12] ; make sure all bytes were read

je read_ok

mov ax,1 ; else return 1 for not OK

jmp short read_err

read_ok: xor ax,ax ; return zero for OK

read_err: pop ds ; restore registers and exit

pop es

pop dx

pop cx

pop bx

pop di

pop si

pop bp

ret

_jdos_read endp

;

; short far jdos_write (short handle, void far * buffer, unsigned short count)

;

; Write to file

;

_jdos_write proc far

push bp ; linkage

mov bp,sp

push si ; save all registers for safety

push di

push bx

push cx

push dx

push es

push ds

mov bx,word ptr [bp+6] ; file handle

lds dx,dword ptr [bp+8] ; buffer address

mov cx,word ptr [bp+12] ; number of bytes

mov ah,40h ; write file

int 21h

jc write_err ; if failed, return error code

cmp ax,word ptr [bp+12] ; make sure all bytes written

je write_ok

mov ax,1 ; else return 1 for not OK

jmp short write_err

write_ok: xor ax,ax ; return zero for OK

write_err: pop ds ; restore registers and exit

pop es

pop dx

pop cx

pop bx

pop di

pop si

pop bp

ret

_jdos_write endp

;

; void far jxms_getdriver (XMSDRIVER far *)

;

; Get the address of the XMS driver, or NULL if not available

;

_jxms_getdriver proc far

push bp ; linkage

mov bp,sp

push si ; save all registers for safety

push di

push bx

push cx

push dx

push es

push ds

mov ax,4300h ; call multiplex interrupt with

int 2fh ; a magic cookie, hex 4300

cmp al,80h ; AL should contain hex 80

je xmsavail

xor dx,dx ; no XMS driver available

xor ax,ax ; return a nil pointer

jmp short xmsavail_done

xmsavail: mov ax,4310h ; fetch driver address with

int 2fh ; another magic cookie

mov dx,es ; copy address to dx:ax

mov ax,bx

xmsavail_done: les bx,dword ptr [bp+6] ; get pointer to return value

mov word ptr es:[bx],ax

mov word ptr es:[bx+2],dx

pop ds ; restore registers and exit

pop es

pop dx

pop cx

pop bx

pop di

pop si

pop bp

ret

_jxms_getdriver endp

;

; void far jxms_calldriver (XMSDRIVER, XMScontext far *)

;

; The XMScontext structure contains values for the AX,DX,BX,SI,DS registers.

; These are loaded, the XMS call is performed, and the new values of the

; AX,DX,BX registers are written back to the context structure.

;

_jxms_calldriver proc far

push bp ; linkage

mov bp,sp

push si ; save all registers for safety

push di

push bx

push cx

push dx

push es

push ds

les bx,dword ptr [bp+10] ; get XMScontext pointer

mov ax,word ptr es:[bx] ; load registers

mov dx,word ptr es:[bx+2]

mov si,word ptr es:[bx+6]

mov ds,word ptr es:[bx+8]

mov bx,word ptr es:[bx+4]

call dword ptr [bp+6] ; call the driver

mov cx,bx ; save returned BX for a sec

les bx,dword ptr [bp+10] ; get XMScontext pointer

mov word ptr es:[bx],ax ; put back ax,dx,bx

mov word ptr es:[bx+2],dx

mov word ptr es:[bx+4],cx

pop ds ; restore registers and exit

pop es

pop dx

pop cx

pop bx

pop di

pop si

pop bp

ret

_jxms_calldriver endp

;

; short far jems_available (void)

;

; Have we got an EMS driver? (this comes straight from the EMS 4.0 specs)

;

_jems_available proc far

push si ; save all registers for safety

push di

push bx

push cx

push dx

push es

push ds

mov ax,3567h ; get interrupt vector 67h

int 21h

push cs

pop ds

mov di,000ah ; check offs 10 in returned seg

lea si,ASCII_device_name ; against literal string

mov cx,8

cld

repe cmpsb

jne no_ems

mov ax,1 ; match, it's there

jmp short avail_done

no_ems: xor ax,ax ; it's not there

avail_done: pop ds ; restore registers and exit

pop es

pop dx

pop cx

pop bx

pop di

pop si

ret

ASCII_device_name db "EMMXXXX0"

_jems_available endp

;

; void far jems_calldriver (EMScontext far *)

;

; The EMScontext structure contains values for the AX,DX,BX,SI,DS registers.

; These are loaded, the EMS trap is performed, and the new values of the

; AX,DX,BX registers are written back to the context structure.

;

_jems_calldriver proc far

push bp ; linkage

mov bp,sp

push si ; save all registers for safety

push di

push bx

push cx

push dx

push es

push ds

les bx,dword ptr [bp+6] ; get EMScontext pointer

mov ax,word ptr es:[bx] ; load registers

mov dx,word ptr es:[bx+2]

mov si,word ptr es:[bx+6]

mov ds,word ptr es:[bx+8]

mov bx,word ptr es:[bx+4]

int 67h ; call the EMS driver

mov cx,bx ; save returned BX for a sec

les bx,dword ptr [bp+6] ; get EMScontext pointer

mov word ptr es:[bx],ax ; put back ax,dx,bx

mov word ptr es:[bx+2],dx

mov word ptr es:[bx+4],cx

pop ds ; restore registers and exit

pop es

pop dx

pop cx

pop bx

pop di

pop si

pop bp

ret

_jems_calldriver endp

JMEMDOSA_TXT ends

end