Category : C Source Code
Archive   : XLIB06.ZIP
Filename : XFILEIO.ASM

;-----------------------------------------------------------------------
; MODULE XFILEIO
;
; Sequential binary file I/O functions
;
; Some functions based on a r.g.p post by Joshua Jensen
;
; Compile with Tasm.
; C callable.
;
;
; ****** XLIB - Mode X graphics library ****************
; ****** ****************
; ****** Written By Themie Gouthas ****************
;
; [email protected]
; [email protected]
;-----------------------------------------------------------------------
COMMENT $


$

LOCALS
.286

include model.inc
include xfileio.inc
.data

_file_err dw (?) ; error value

.code

PUSH_DS macro
IFNDEF s
push ds
ENDIF
endm

POP_DS macro
IFNDEF s
pop ds
ENDIF
endm

LDS_M macro arg1,arg2
IFNDEF s
lds &arg1&,&arg2&
ELSE
mov &arg1&,word ptr &arg2&
ENDIF
endm



;****************************************************************
;
; name: f_open
;
; C Prototype:
;
; extern int f_open(char * filename, char access)
;
; Opens a file according to the access char:
;
; 0 = read only - If doesnt exist return error
; 1 = write only - If doesnt exist create it otherwise clear it
; 2 = read/write - If doesnt exist create it
;
; Returns the file handle on success, -1 on failure
;
;
proc _f_open
IFNDEF s
ARG filename:dword,access:byte
ELSE
ARG filename:word,access:byte
ENDIF
push bp ; Preserve caller's stack frame
mov bp,sp
PUSH_DS
LDS_M dx,[filename] ; point DS:DX to file name string
mov [_file_err],0
cmp [access],1
je @@creat

mov ah,3dh ; select "open file" DOS service
mov al,[access] ; select access type code
int 21h ; call DOS service
jnb @@Done ; If carry flag set we have failed


cmp [access],2
jne @@error
@@creat:
mov ah,3ch ; select "creat file" DOS service
mov cx,0
int 21h ; call DOS service
jnb @@Done ; If carry flag set we have failed
@@error:
mov [_file_err],ax
mov ax,-1 ; indicate failure
@@Done: ; otherwise return file handle
POP_DS
pop bp ;restore caller's stack frame
ret
_f_open endp


;****************************************************************
;
; name: f_close
;
; C Prototype:
;
; extern int f_close(int handle)
;
; Closes the file associated with the specified handle
;
; Returns 0 on success, -1 on failure
;
proc _f_close
ARG handle:word
push bp ; Preserve caller's stack frame
mov bp,sp

mov [_file_err],0 ; Clear error
mov ah,3eh ; select "close file handle" DOS service
mov bx,[handle] ; select handle of file to close
int 21h ; call DOS service
jnb @@Fix ; failed if carry flag set
mov [_file_err],ax;
mov ax,-1 ; return error
jmp short @@Done
@@Fix: ; otherwise
xor ax,ax ; return 0
@@Done:
pop bp ;restore caller's stack frame
ret
_f_close endp


;****************************************************************
;
; name: f_read
;
; C Prototype:
;
; extern int f_read(int handle, char *buffer, int count)
;
; Reads a block of count bytes from the file specified by the handle
; into the buffer
;
; Returns count on success, failure is detectable via _file_err
;
proc _f_read
IFNDEF s
ARG handle:word,buffer:dword,count:word
ELSE
ARG handle:word,buffer:word,count:word
ENDIF
push bp ; Preserve caller's stack frame
mov bp,sp
PUSH_DS

mov [_file_err],0 ; Clear error
mov ah,3fh ; select "read from file or device" DOS service
mov bx,[handle] ; select handle of file to close
mov cx,[count]
LDS_M dx,[buffer]
int 21h ; call DOS service
jnb @@Done ; failed if carry flag set
mov [_file_err],ax
xor ax,ax ; return error
jmp short @@Done
@@Done:
POP_DS
pop bp ;restore caller's stack frame
ret
_f_read endp

;****************************************************************
;
; name: f_write
;
; C Prototype:
;
; extern int f_write(int handle, char *buffer, int count)
;
; Writes a block of count bytes to the file specified by the handle
; from the buffer
;
; Returns count on success, error is indicated by _file_err iff count = 0
;
proc _f_write
IFNDEF s
ARG handle:word,buffer:dword,count:word
ELSE
ARG handle:word,buffer:word,count:word
ENDIF
push bp ; Preserve caller's stack frame
mov bp,sp
PUSH_DS

mov [_file_err],0 ; Clear error
mov ah,40h ; select "write to file or device" DOS service
mov bx,[handle] ; select handle of file to write
mov cx,[count]
LDS_M dx,[buffer]
int 21h ; call DOS service
jnb @@Done ; has the function failed ?
mov [_file_err],ax
xor ax,ax ; yes, return error
jmp short @@Done
@@Done: ; otherwise return bytes written
POP_DS
pop bp ; restore caller's stack frame
ret
_f_write endp

;****************************************************************
;
; name: f_readfar
;
; C Prototype:
;
; extern int f_readfar(int handle, char far * buffer, int count)
;
; Reads a block of count bytes from the file specified by the handle
; into the buffer
;
; Returns count on success, failure is detectable via _file_err
;
proc _f_readfar
ARG handle:word,buffer:dword,count:word
push bp ; Preserve caller's stack frame
mov bp,sp
push ds

mov [_file_err],0 ; Clear error
mov ah,3fh ; select "read from file or device" DOS service
mov bx,[handle] ; select handle of file to close
mov cx,[count]
lds dx,[buffer]
int 21h ; call DOS service
jnb @@Done ; failed if carry flag set
mov [_file_err],ax
xor ax,ax ; return error
jmp short @@Done
@@Done:
pop ds
pop bp ;restore caller's stack frame
ret
_f_readfar endp

;****************************************************************
;
; name: f_writefar
;
; C Prototype:
;
; extern int f_writefar(int handle, char far * buffer, int count)
;
; Writes a block of count bytes to the file specified by the handle
; from the buffer
;
; Returns count on success, error is indicated by _file_err iff count = 0
;
proc _f_writefar
ARG handle:word,buffer:dword,count:word
push bp ; Preserve caller's stack frame
mov bp,sp
push ds

mov [_file_err],0 ; Clear error
mov ah,40h ; select "write to file or device" DOS service
mov bx,[handle] ; select handle of file to write
mov cx,[count]
lds dx,[buffer]
int 21h ; call DOS service
jnb @@Done ; has the function failed ?
mov [_file_err],ax
xor ax,ax ; yes, return error
jmp short @@Done
@@Done: ; otherwise return bytes written
pop ds
pop bp ; restore caller's stack frame
ret
_f_writefar endp



;****************************************************************
;
; name: f_seek
;
; C Prototype:
;
; extern long int f_seek(int handle, long int position, char method_code)
;
; Moves the file pointer according to the position and method code
;
; Returns file pointer position on success, -1 on failure
;
proc _f_seek
ARG handle:word,position:dword,method_code:byte
push bp ; Preserve caller's stack frame
mov bp,sp

mov [_file_err],0 ; Clear error
mov ah,42h ; select "move file pointer" DOS service
mov bx,[handle] ; select handle of file to close
mov al,[method_code]
mov cx,word ptr [position+2]
mov dx,word ptr [position]
int 21h ; call DOS service
jnb @@Done ; has the function failed ?
mov [_file_err],ax
mov ax,-1 ; yes, return error
mov dx,-1 ;
jmp short @@Done
@@Done: ; otherwise return bytes written
pop bp ; restore caller's stack frame
ret
_f_seek endp

;****************************************************************
;
; name: f_tell
;
; C Prototype:
;
; extern long int f_tell(int handle)
;
; Returns file pointer position on success, -1 on failure
;
proc _f_tell
ARG handle:word,position:dword,method_code:byte
push bp ; Preserve caller's stack frame
mov bp,sp

mov [_file_err],0 ; Clear error
mov ah,42h ; select "move file pointer" DOS service
mov bx,[handle] ; select handle of file to close
xor dx,dx
mov cx,dx
int 21h
jnb @@Done
mov [_file_err],ax
mov ax,-1 ; yes, return error
mov dx,-1 ;
jmp short @@Done
@@Done: ; otherwise return bytes written
pop bp ; restore caller's stack frame
ret
_f_tell endp


;****************************************************************
;
; name: f_filelength
;
; C Prototype:
;
; extern long int f_filelength(int handle)
;
; Returns the length of the file associated with the specified handle
;
; Returns file length on success, -1 on failure
;
proc _f_filelength
ARG handle:word
LOCAL low:word,high:word=LocalStk
push bp ; Preserve caller's stack frame
mov bp,sp
sub sp,LocalStk

mov [_file_err],0 ; Clear error

; Get ptr's current location in file and save it

mov ah,42h ; select "move file pointer" DOS service
mov al,1 ; select "from current location" method
mov bx,[handle] ; select handle of file to close
xor cx,cx
xor dx,dx
int 21h
jb @@Error
mov [low],ax
mov [high],dx

; Get ptr's value at end of file

mov ah,42h ; select "move file pointer" DOS service
mov al,2 ; select "from end of file" method
mov bx,[handle] ; select handle of file to close
xor cx,cx
xor dx,dx
int 21h
jb @@Error

; Save the results while returning pointer to its previous location

push ax
push dx

mov ah,42h ; select "move file pointer" DOS service
mov al,0 ; select "from start of file" method
mov bx,[handle] ; select handle of file to close
mov cx,[high]
mov dx,[low]
int 21h

; restore resultant length

pop dx
pop ax

jnb @@Done ; Was the operation a success ?
@@Error:
mov [_file_err],ax
mov ax,-1 ; no, return error
mov dx,-1 ;
@@Done: ; otherwise return bytes written
mov sp,bp
pop bp ; restore caller's stack frame
ret
_f_filelength endp


end