; more source code at http://www.ahjoe.com/source/srcdown.asp

        PUBLIC  FOPEN, FSIZE, FREAD, FWRITE, FCREATE, FPOS, FCLOSE
CODE    SEGMENT
        ASSUME  CS:CODE

FCLOSE  PROC    FAR
; IN:
;     AX=FILE NO.
        PUSH    BX
        MOV     BX, AX
        MOV     AH, 3EH
        INT     21H
        POP     BX
        RETF
FCLOSE  ENDP

FOPEN   PROC    FAR
; IN:
;     DS:DX=FILE NAME
;     AL=OPEN MODE
; OUT:
;     CF=0   AX=FILE NUM
;     CF=1   AX=ERROR CODE

        MOV     AH, 3DH
        INT     21H
        RETF

FOPEN   ENDP

FSIZE   PROC    FAR
; IN:
;     AX=FILE NUM
; OUT:
;     CF=0  DX:AX=FILE_SIZE
;     CF=1  AX=ERROR CODE

        PUSH    BX
        PUSH    CX
        MOV     BX, AX
        MOV     AX, 4202H
        XOR     CX, CX
        MOV     DX, CX
        INT     21H
        PUSH    AX
        PUSH    DX
        MOV     CX, 0
        MOV     DX, 0
        MOV     AX, 4200H
        INT     21H
        POP     DX
        POP     AX
        POP     CX
        POP     BX
        RETF
FSIZE   ENDP

FREAD   PROC    NEAR
; IN:
;     DS:DX=DATA BUFFER
;     AX=FILE NUM
;     CX=LENGTH
; OUT:
;     CF=0  AX=READ SIZE
;     CF=1  AX=ERROR CODE

        PUSH    BX
        MOV     BX, AX
        MOV     AH, 3FH
        INT     21H
        POP     BX
        RETF
FREAD   ENDP

FWRITE  PROC    FAR
; IN:
;     DS:DX=DATA BUFFER
;     AX=FILE NUM
;     CX=LENGTH
; OUT:
;     CF=0  AX=WRITE SIZE
;     CF=1  AX=ERROR CODE

        PUSH    BX
        MOV     BX, AX
        MOV     AH, 40H
        INT     21H
        POP     BX
        RETF
FWRITE  ENDP

FCREATE PROC    FAR
; IN:
;     DS:DX=FILE NAME
; OUT:
;     CF=0  AX=FILE NUM
;     CF=1  AX=ERROR CODE

        MOV     CX, 0
        MOV     AH, 3CH
        INT     21H
        RETF
FCREATE ENDP

FPOS    PROC    FAR
; IN:
;     AL=MODE
;     BX=FILE NUM
;     CX:DX=NEW POSITION
; OUT:
;     DX:AX=NEW POSITION
        MOV     AH,42H
        INT     21H
        RETF
FPOS    ENDP

CODE    ENDS
        END     FOPEN