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; Copyright (C) 1992, Thomas G. Lane.
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; This file is part of the Independent JPEG Group's software.
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; For conditions of distribution and use, see the accompanying README file.
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; This file contains low-level interface routines to support the MS-DOS
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; backing store manager (jmemdos.c). Routines are provided to access disk
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; files through direct DOS calls, and to access XMS and EMS drivers.
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; This file should assemble with Microsoft's MASM or any compatible
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; assembler (including Borland's Turbo Assembler). If you haven't got
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; a compatible assembler, better fall back to jmemansi.c or jmemname.c.
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; To minimize dependence on the C compiler's register usage conventions,
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; we save and restore all 8086 registers, even though most compilers only
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; require SI,DI,DS to be preserved. Also, we use only 16-bit-wide return
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; values, which everybody returns in AX.
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; Based on code contributed by Ge' Weijers.
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JMEMDOSA_TXT segment byte public 'CODE'
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assume cs:JMEMDOSA_TXT
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public _jxms_getdriver
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public _jxms_calldriver
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public _jems_available
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public _jems_calldriver
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; short far jdos_open (short far * handle, char far * filename)
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; Create and open a temporary file
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push si ; save all registers for safety
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mov cx,0 ; normal file attributes
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lds dx,dword ptr [bp+10] ; get filename pointer
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mov ah,3ch ; create file
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jc open_err ; if failed, return error code
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lds bx,dword ptr [bp+6] ; get handle pointer
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mov word ptr [bx],ax ; save the handle
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xor ax,ax ; return zero for OK
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open_err: pop ds ; restore registers and exit
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; short far jdos_close (short handle)
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; Close the file handle
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push si ; save all registers for safety
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mov bx,word ptr [bp+6] ; file handle
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mov ah,3eh ; close file
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jc close_err ; if failed, return error code
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xor ax,ax ; return zero for OK
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close_err: pop ds ; restore registers and exit
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; short far jdos_seek (short handle, long offset)
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push si ; save all registers for safety
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mov bx,word ptr [bp+6] ; file handle
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mov dx,word ptr [bp+8] ; LS offset
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mov cx,word ptr [bp+10] ; MS offset
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mov ax,4200h ; absolute seek
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jc seek_err ; if failed, return error code
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xor ax,ax ; return zero for OK
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seek_err: pop ds ; restore registers and exit
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; short far jdos_read (short handle, void far * buffer, unsigned short count)
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push si ; save all registers for safety
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mov bx,word ptr [bp+6] ; file handle
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lds dx,dword ptr [bp+8] ; buffer address
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mov cx,word ptr [bp+12] ; number of bytes
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mov ah,3fh ; read file
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jc read_err ; if failed, return error code
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cmp ax,word ptr [bp+12] ; make sure all bytes were read
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mov ax,1 ; else return 1 for not OK
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read_ok: xor ax,ax ; return zero for OK
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read_err: pop ds ; restore registers and exit
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; short far jdos_write (short handle, void far * buffer, unsigned short count)
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push si ; save all registers for safety
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mov bx,word ptr [bp+6] ; file handle
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lds dx,dword ptr [bp+8] ; buffer address
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mov cx,word ptr [bp+12] ; number of bytes
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mov ah,40h ; write file
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jc write_err ; if failed, return error code
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cmp ax,word ptr [bp+12] ; make sure all bytes written
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mov ax,1 ; else return 1 for not OK
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write_ok: xor ax,ax ; return zero for OK
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write_err: pop ds ; restore registers and exit
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; void far jxms_getdriver (XMSDRIVER far *)
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; Get the address of the XMS driver, or NULL if not available
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_jxms_getdriver proc far
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push si ; save all registers for safety
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mov ax,4300h ; call multiplex interrupt with
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int 2fh ; a magic cookie, hex 4300
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cmp al,80h ; AL should contain hex 80
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xor dx,dx ; no XMS driver available
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xor ax,ax ; return a nil pointer
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jmp short xmsavail_done
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xmsavail: mov ax,4310h ; fetch driver address with
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int 2fh ; another magic cookie
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mov dx,es ; copy address to dx:ax
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xmsavail_done: les bx,dword ptr [bp+6] ; get pointer to return value
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mov word ptr es:[bx],ax
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mov word ptr es:[bx+2],dx
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pop ds ; restore registers and exit
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; void far jxms_calldriver (XMSDRIVER, XMScontext far *)
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; The XMScontext structure contains values for the AX,DX,BX,SI,DS registers.
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; These are loaded, the XMS call is performed, and the new values of the
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; AX,DX,BX registers are written back to the context structure.
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_jxms_calldriver proc far
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push si ; save all registers for safety
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les bx,dword ptr [bp+10] ; get XMScontext pointer
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mov ax,word ptr es:[bx] ; load registers
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mov dx,word ptr es:[bx+2]
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mov si,word ptr es:[bx+6]
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mov ds,word ptr es:[bx+8]
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mov bx,word ptr es:[bx+4]
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call dword ptr [bp+6] ; call the driver
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mov cx,bx ; save returned BX for a sec
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les bx,dword ptr [bp+10] ; get XMScontext pointer
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mov word ptr es:[bx],ax ; put back ax,dx,bx
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mov word ptr es:[bx+2],dx
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mov word ptr es:[bx+4],cx
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pop ds ; restore registers and exit
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_jxms_calldriver endp
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; short far jems_available (void)
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; Have we got an EMS driver? (this comes straight from the EMS 4.0 specs)
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_jems_available proc far
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push si ; save all registers for safety
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mov ax,3567h ; get interrupt vector 67h
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mov di,000ah ; check offs 10 in returned seg
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lea si,ASCII_device_name ; against literal string
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mov ax,1 ; match, it's there
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no_ems: xor ax,ax ; it's not there
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avail_done: pop ds ; restore registers and exit
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ASCII_device_name db "EMMXXXX0"
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; void far jems_calldriver (EMScontext far *)
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; The EMScontext structure contains values for the AX,DX,BX,SI,DS registers.
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; These are loaded, the EMS trap is performed, and the new values of the
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; AX,DX,BX registers are written back to the context structure.
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_jems_calldriver proc far
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push si ; save all registers for safety
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les bx,dword ptr [bp+6] ; get EMScontext pointer
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mov ax,word ptr es:[bx] ; load registers
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mov dx,word ptr es:[bx+2]
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mov si,word ptr es:[bx+6]
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mov ds,word ptr es:[bx+8]
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mov bx,word ptr es:[bx+4]
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int 67h ; call the EMS driver
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mov cx,bx ; save returned BX for a sec
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les bx,dword ptr [bp+6] ; get EMScontext pointer
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mov word ptr es:[bx],ax ; put back ax,dx,bx
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mov word ptr es:[bx+2],dx
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mov word ptr es:[bx+4],cx
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pop ds ; restore registers and exit
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_jems_calldriver endp
added
removed
jpg/jmemdosa.asm
