;

; 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