JPEGView/Independent JPEG Group/jmemdosa.asm

;
; 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 p