jpeg/jmemdosa.asm

   1 ;
   2 ; jmemdosa.asm
   3 ;
   4 ; Copyright (C) 1992, Thomas G. Lane.
   5 ; This file is part of the Independent JPEG Group's software.
   6 ; For conditions of distribution and use, see the accompanying README file.
   7 ;
   8 ; This file contains low-level interface routines to support the MS-DOS
   9 ; backing store manager (jmemdos.c).  Routines are provided to access disk
  10 ; files through direct DOS calls, and to access XMS and EMS drivers.
  11 ;
  12 ; This file should assemble with Microsoft's MASM or any compatible
  13 ; assembler (including Borland's Turbo Assembler).  If you haven't got
  14 ; a compatible assembler, better fall back to jmemansi.c or jmemname.c.
  15 ;
  16 ; To minimize dependence on the C compiler's register usage conventions,
  17 ; we save and restore all 8086 registers, even though most compilers only
  18 ; require SI,DI,DS to be preserved.  Also, we use only 16-bit-wide return
  19 ; values, which everybody returns in AX.
  20 ;
  21 ; Based on code contributed by Ge' Weijers.
  22 ;
  23
  24 JMEMDOSA_TXT    segment byte public 'CODE'
  25
  26                 assume  cs:JMEMDOSA_TXT
  27
  28                 public  _jdos_open
  29                 public  _jdos_close
  30                 public  _jdos_seek
  31                 public  _jdos_read
  32                 public  _jdos_write
  33                 public  _jxms_getdriver
  34                 public  _jxms_calldriver
  35                 public  _jems_available
  36                 public  _jems_calldriver
  37
  38 ;
  39 ; short far jdos_open (short far * handle, char far * filename)
  40 ;
  41 ; Create and open a temporary file
  42 ;
  43 _jdos_open      proc    far
  44                 push    bp                      ; linkage
  45                 mov     bp,sp
  46                 push    si                      ; save all registers for safety
  47                 push    di
  48                 push    bx
  49                 push    cx
  50                 push    dx
  51                 push    es
  52                 push    ds
  53                 mov     cx,0                    ; normal file attributes
  54                 lds     dx,dword ptr [bp+10]    ; get filename pointer
  55                 mov     ah,3ch                  ; create file
  56                 int     21h
  57                 jc      open_err                ; if failed, return error code
  58                 lds     bx,dword ptr [bp+6]     ; get handle pointer
  59                 mov     word ptr [bx],ax        ; save the handle
  60                 xor     ax,ax                   ; return zero for OK
  61 open_err:       pop     ds                      ; restore registers and exit
  62                 pop     es
  63                 pop     dx
  64                 pop     cx
  65                 pop     bx
  66                 pop     di
  67                 pop     si
  68                 pop     bp
  69                 ret
  70 _jdos_open      endp
  71
  72
  73 ;
  74 ; short far jdos_close (short handle)
  75 ;
  76 ; Close the file handle
  77 ;
  78 _jdos_close     proc    far
  79                 push    bp                      ; linkage
  80                 mov     bp,sp
  81                 push    si                      ; save all registers for safety
  82                 push    di
  83                 push    bx
  84                 push    cx
  85                 push    dx
  86                 push    es
  87                 push    ds
  88                 mov     bx,word ptr [bp+6]      ; file handle
  89                 mov     ah,3eh                  ; close file
  90                 int     21h
  91                 jc      close_err               ; if failed, return error code
  92                 xor     ax,ax                   ; return zero for OK
  93 close_err:      pop     ds                      ; restore registers and exit
  94                 pop     es
  95                 pop     dx
  96                 pop     cx
  97                 pop     bx
  98                 pop     di
  99                 pop     si
 100                 pop     bp
 101                 ret
 102 _jdos_close     endp
 103
 104
 105 ;
 106 ; short far jdos_seek (short handle, long offset)
 107 ;
 108 ; Set file position
 109 ;
 110 _jdos_seek      proc    far
 111                 push    bp                      ; linkage
 112                 mov     bp,sp
 113                 push    si                      ; save all registers for safety
 114                 push    di
 115                 push    bx
 116                 push    cx
 117                 push    dx
 118                 push    es
 119                 push    ds
 120                 mov     bx,word ptr [bp+6]      ; file handle
 121                 mov     dx,word ptr [bp+8]      ; LS offset
 122                 mov     cx,word ptr [bp+10]     ; MS offset
 123                 mov     ax,4200h                ; absolute seek
 124                 int     21h
 125                 jc      seek_err                ; if failed, return error code
 126                 xor     ax,ax                   ; return zero for OK
 127 seek_err:       pop     ds                      ; restore registers and exit
 128                 pop     es
 129                 pop     dx
 130                 pop     cx
 131                 pop     bx
 132                 pop     di
 133                 pop     si
 134                 pop     bp
 135                 ret
 136 _jdos_seek      endp
 137
 138
 139 ;
 140 ; short far jdos_read (short handle, void far * buffer, unsigned short count)
 141 ;
 142 ; Read from file
 143 ;
 144 _jdos_read      proc    far
 145                 push    bp                      ; linkage
 146                 mov     bp,sp
 147                 push    si                      ; save all registers for safety
 148                 push    di
 149                 push    bx
 150                 push    cx
 151                 push    dx
 152                 push    es
 153                 push    ds
 154                 mov     bx,word ptr [bp+6]      ; file handle
 155                 lds     dx,dword ptr [bp+8]     ; buffer address
 156                 mov     cx,word ptr [bp+12]     ; number of bytes
 157                 mov     ah,3fh                  ; read file
 158                 int     21h
 159                 jc      read_err                ; if failed, return error code
 160                 cmp     ax,word ptr [bp+12]     ; make sure all bytes were read
 161                 je      read_ok
 162                 mov     ax,1                    ; else return 1 for not OK
 163                 jmp     short read_err
 164 read_ok:        xor     ax,ax                   ; return zero for OK
 165 read_err:       pop     ds                      ; restore registers and exit
 166                 pop     es
 167                 pop     dx
 168                 pop     cx
 169                 pop     bx
 170                 pop     di
 171                 pop     si
 172                 pop     bp
 173                 ret
 174 _jdos_read      endp
 175
 176
 177 ;
 178 ; short far jdos_write (short handle, void far * buffer, unsigned short count)
 179 ;
 180 ; Write to file
 181 ;
 182 _jdos_write     proc    far
 183                 push    bp                      ; linkage
 184                 mov     bp,sp
 185                 push    si                      ; save all registers for safety
 186                 push    di
 187                 push    bx
 188                 push    cx
 189                 push    dx
 190                 push    es
 191                 push    ds
 192                 mov     bx,word ptr [bp+6]      ; file handle
 193                 lds     dx,dword ptr [bp+8]     ; buffer address
 194                 mov     cx,word ptr [bp+12]     ; number of bytes
 195                 mov     ah,40h                  ; write file
 196                 int     21h
 197                 jc      write_err               ; if failed, return error code
 198                 cmp     ax,word ptr [bp+12]     ; make sure all bytes written
 199                 je      write_ok
 200                 mov     ax,1                    ; else return 1 for not OK
 201                 jmp     short write_err
 202 write_ok:       xor     ax,ax                   ; return zero for OK
 203 write_err:      pop     ds                      ; restore registers and exit
 204                 pop     es
 205                 pop     dx
 206                 pop     cx
 207                 pop     bx
 208                 pop     di
 209                 pop     si
 210                 pop     bp
 211                 ret
 212 _jdos_write     endp
 213
 214
 215 ;
 216 ; void far jxms_getdriver (XMSDRIVER far *)
 217 ;
 218 ; Get the address of the XMS driver, or NULL if not available
 219 ;
 220 _jxms_getdriver proc    far
 221                 push    bp                      ; linkage
 222                 mov     bp,sp
 223                 push    si                      ; save all registers for safety
 224                 push    di
 225                 push    bx
 226                 push    cx
 227                 push    dx
 228                 push    es
 229                 push    ds
 230                 mov     ax,4300h                ; call multiplex interrupt with
 231                 int     2fh                     ; a magic cookie, hex 4300
 232                 cmp     al,80h                  ; AL should contain hex 80
 233                 je      xmsavail
 234                 xor     dx,dx                   ; no XMS driver available
 235                 xor     ax,ax                   ; return a nil pointer
 236                 jmp     short xmsavail_done
 237 xmsavail:       mov     ax,4310h                ; fetch driver address with
 238                 int     2fh                     ; another magic cookie
 239                 mov     dx,es                   ; copy address to dx:ax
 240                 mov     ax,bx
 241 xmsavail_done:  les     bx,dword ptr [bp+6]     ; get pointer to return value
 242                 mov     word ptr es:[bx],ax
 243                 mov     word ptr es:[bx+2],dx
 244                 pop     ds                      ; restore registers and exit
 245                 pop     es
 246                 pop     dx
 247                 pop     cx
 248                 pop     bx
 249                 pop     di
 250                 pop     si
 251                 pop     bp
 252                 ret
 253 _jxms_getdriver endp
 254
 255
 256 ;
 257 ; void far jxms_calldriver (XMSDRIVER, XMScontext far *)
 258 ;
 259 ; The XMScontext structure contains values for the AX,DX,BX,SI,DS registers.
 260 ; These are loaded, the XMS call is performed, and the new values of the
 261 ; AX,DX,BX registers are written back to the context structure.
 262 ;
 263 _jxms_calldriver        proc    far
 264                 push    bp                      ; linkage
 265                 mov     bp,sp
 266                 push    si                      ; save all registers for safety
 267                 push    di
 268                 push    bx
 269                 push    cx
 270                 push    dx
 271                 push    es
 272                 push    ds
 273                 les     bx,dword ptr [bp+10]    ; get XMScontext pointer
 274                 mov     ax,word ptr es:[bx]     ; load registers
 275                 mov     dx,word ptr es:[bx+2]
 276                 mov     si,word ptr es:[bx+6]
 277                 mov     ds,word ptr es:[bx+8]
 278                 mov     bx,word ptr es:[bx+4]
 279                 call    dword ptr [bp+6]        ; call the driver
 280                 mov     cx,bx                   ; save returned BX for a sec
 281                 les     bx,dword ptr [bp+10]    ; get XMScontext pointer
 282                 mov     word ptr es:[bx],ax     ; put back ax,dx,bx
 283                 mov     word ptr es:[bx+2],dx
 284                 mov     word ptr es:[bx+4],cx
 285                 pop     ds                      ; restore registers and exit
 286                 pop     es
 287                 pop     dx
 288                 pop     cx
 289                 pop     bx
 290                 pop     di
 291                 pop     si
 292                 pop     bp
 293                 ret
 294 _jxms_calldriver        endp
 295
 296
 297 ;
 298 ; short far jems_available (void)
 299 ;
 300 ; Have we got an EMS driver? (this comes straight from the EMS 4.0 specs)
 301 ;
 302 _jems_available proc    far
 303                 push    si                      ; save all registers for safety
 304                 push    di
 305                 push    bx
 306                 push    cx
 307                 push    dx
 308                 push    es
 309                 push    ds
 310                 mov     ax,3567h                ; get interrupt vector 67h
 311                 int     21h
 312                 push    cs
 313                 pop     ds
 314                 mov     di,000ah                ; check offs 10 in returned seg
 315                 lea     si,ASCII_device_name    ; against literal string
 316                 mov     cx,8
 317                 cld
 318                 repe cmpsb
 319                 jne     no_ems
 320                 mov     ax,1                    ; match, it's there
 321                 jmp     short avail_done
 322 no_ems:         xor     ax,ax                   ; it's not there
 323 avail_done:     pop     ds                      ; restore registers and exit
 324                 pop     es
 325                 pop     dx
 326                 pop     cx
 327                 pop     bx
 328                 pop     di
 329                 pop     si
 330                 ret
 331
 332 ASCII_device_name       db      "EMMXXXX0"
 333
 334 _jems_available endp
 335
 336
 337 ;
 338 ; void far jems_calldriver (EMScontext far *)
 339 ;
 340 ; The EMScontext structure contains values for the AX,DX,BX,SI,DS registers.
 341 ; These are loaded, the EMS trap is performed, and the new values of the
 342 ; AX,DX,BX registers are written back to the context structure.
 343 ;
 344 _jems_calldriver        proc far
 345                 push    bp                      ; linkage
 346                 mov     bp,sp
 347                 push    si                      ; save all registers for safety
 348                 push    di
 349                 push    bx
 350                 push    cx
 351                 push    dx
 352                 push    es
 353                 push    ds
 354                 les     bx,dword ptr [bp+6]     ; get EMScontext pointer
 355                 mov     ax,word ptr es:[bx]     ; load registers
 356                 mov     dx,word ptr es:[bx+2]
 357                 mov     si,word ptr es:[bx+6]
 358                 mov     ds,word ptr es:[bx+8]
 359                 mov     bx,word ptr es:[bx+4]
 360                 int     67h                     ; call the EMS driver
 361                 mov     cx,bx                   ; save returned BX for a sec
 362                 les     bx,dword ptr [bp+6]     ; get EMScontext pointer
 363                 mov     word ptr es:[bx],ax     ; put back ax,dx,bx
 364                 mov     word ptr es:[bx+2],dx
 365                 mov     word ptr es:[bx+4],cx
 366                 pop     ds                      ; restore registers and exit
 367                 pop     es
 368                 pop     dx
 369                 pop     cx
 370                 pop     bx
 371                 pop     di
 372                 pop     si
 373                 pop     bp
 374                 ret
 375 _jems_calldriver        endp
 376
 377 JMEMDOSA_TXT    ends
 378
 379                 end