source: xtideuniversalbios/trunk/Assembly_Library/Src/File/FileIO.asm @ 51

; File name     :   FileIO.asm
; Project name  :   Assembly Library
; Created date  :   1.9.2010
; Last update   :   10.10.2010
; Author        :   Tomi Tilli
; Description   :   Functions for file access.

; Section containing code
SECTION .text

;--------------------------------------------------------------------
; FileIO_OpenWithPathInDSSIandFileAccessInAL
;   Parameters:
;       AL:     FILE_ACCESS.(mode)
;       DS:SI:  Ptr to NULL terminated path or file name
;   Returns:
;       AX:     DOS error code if CF set
;       BX:     File handle if CF cleared
;       CF:     Clear if file opened successfully
;               Set if error
;   Corrupts registers:
;       AX, BX
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
FileIO_OpenWithPathInDSSIandFileAccessInAL:
    xchg    dx, si      ; Path now in DS:DX
    mov     ah, OPEN_EXISTING_FILE
    int     DOS_INTERRUPT_21h
    xchg    si, dx
    mov     bx, ax      ; Copy file handle to BX
    ret


;--------------------------------------------------------------------
; FileIO_CloseUsingHandleFromBX
;   Parameters:
;       BX:     File handle
;   Returns:
;       AX:     DOS error code if CF set
;       CF:     Clear if file closed successfully
;               Set if error
;   Corrupts registers:
;       AX
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
FileIO_CloseUsingHandleFromBX:
    mov     ah, CLOSE_FILE
    int     DOS_INTERRUPT_21h
    ret


;--------------------------------------------------------------------
; File position is updated so next read will start where
; previous read stopped.
; 
; FileIO_ReadCXbytesToDSSIusingHandleFromBX
;   Parameters:
;       BX:     File handle
;       CX:     Number of bytes to read
;       DS:SI:  Ptr to destination buffer
;   Returns:
;       AX:     Number of bytes actually read if successfull (0 if at EOF before call)
;               DOS error code if CF set
;       CF:     Clear if successfull
;               Set if error
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
FileIO_ReadCXbytesToDSSIusingHandleFromBX:
    xchg    dx, si              ; DS:DX now points to destination buffer
    mov     ah, READ_FROM_FILE_OR_DEVICE
    int     DOS_INTERRUPT_21h
    xchg    si, dx
    ret


;--------------------------------------------------------------------
; File position is updated so next write will start where
; previous write stopped.
; 
; FileIO_WriteCXbytesFromDSSIusingHandleFromBX:
;   Parameters:
;       BX:     File handle
;       CX:     Number of bytes to write
;       DS:SI:  Ptr to source buffer
;   Returns:
;       AX:     Number of bytes actually written if successfull (EOF check)
;               DOS error code if CF set
;       CF:     Clear if successfull
;               Set if error
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
FileIO_WriteCXbytesFromDSSIusingHandleFromBX:
    xchg    dx, si              ; DS:DX now points to source buffer
    mov     ah, WRITE_TO_FILE_OR_DEVICE
    int     DOS_INTERRUPT_21h
    xchg    si, dx
    ret


;--------------------------------------------------------------------
; FileIO_GetFileSizeToDXAXusingHandleFromBXandResetFilePosition:
;   Parameters:
;       BX:     File handle
;   Returns:
;       DX:AX:  Signed file size (if CF cleared)
;       AX:     DOS error code (if CF set)
;       CF:     Clear if successfull
;               Set if error
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
FileIO_GetFileSizeToDXAXusingHandleFromBXandResetFilePosition:
    push    cx

    ; Get file size to DX:AX
    xor     cx, cx
    xor     dx, dx
    mov     al, SEEK_FROM.endOfFile
    call    FileIO_SeekFromOriginInALtoOffsetInDXAXusingHandleFromBX
    jc      SHORT .ReturnFileError
    push    dx
    push    ax

    ; Reset file position
    xor     dx, dx
    mov     al, SEEK_FROM.startOfFile
    call    FileIO_SeekFromOriginInALtoOffsetInDXAXusingHandleFromBX
    pop     ax
    pop     dx

.ReturnFileError:
    pop     cx
    ret


;--------------------------------------------------------------------
; FileIO_SeekFromOriginInALtoOffsetInDXAXusingHandleFromBX:
;   Parameters:
;       AL:     SEEK_FROM.(origin)
;       BX:     File handle
;       CX:DX:  Signed offset to seek starting from AL
;   Returns:
;       DX:AX:  New file position in bytes from start of file (if CF cleared)
;       AX:     DOS error code (if CF set)
;       CF:     Clear if successfull
;               Set if error
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
FileIO_SeekFromOriginInALtoOffsetInDXAXusingHandleFromBX:
    mov     ah, SET_CURRENT_FILE_POSITION
    int     DOS_INTERRUPT_21h
    ret