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cc65/libsrc/cbm/cbm_read.s

114 lines
2.6 KiB
ArmAsm

;
; Ullrich von Bassewitz, 22.06.2002
;
; Original C code by Marc 'BlackJack' Rintsch, 19.03.2001
;
; int __fastcall__ cbm_read (unsigned char lfn, void* buffer, unsigned int size)
; /* Reads up to "size" bytes from a file to "buffer".
; ** Returns the number of actually read bytes, 0 if there are no bytes left
; ** (EOF) or -1 in case of an error. __oserror contains an errorcode then (see
; ** table below).
; */
; {
; static unsigned int bytesread;
; static unsigned char tmp;
;
; /* if we can't change to the inputchannel #lfn then return an error */
; if (__oserror = cbm_k_chkin(lfn)) return -1;
;
; bytesread = 0;
;
; while (bytesread<size && !cbm_k_readst()) {
; tmp = cbm_k_basin();
;
; /* the kernal routine BASIN sets ST to EOF if the end of file
; ** is reached the first time, then we have store tmp.
; ** every subsequent call returns EOF and READ ERROR in ST, then
; ** we have to exit the loop here immediatly.
; */
; if (cbm_k_readst() & 0xBF) break;
;
; ((unsigned char*)buffer)[bytesread++] = tmp;
; }
;
; cbm_k_clrch();
; return bytesread;
; }
;
.include "cbm.inc"
.export _cbm_read
.importzp ptr1, ptr2, ptr3, tmp1
.import popax, popa
.import ___oserror
_cbm_read:
inx
stx ptr1+1
tax
inx
stx ptr1 ; Save size with both bytes incremented separately.
jsr popax
sta ptr2
stx ptr2+1 ; Save buffer
jsr popa
tax
jsr CHKIN
bcs @E1 ; Branch on error
; bytesread = 0;
lda #$00
sta ptr3
sta ptr3+1
beq @L3 ; Branch always
; Loop
@L1: jsr READST
cmp #0 ; Status ok?
bne @L4
jsr BASIN ; Read next char from file
sta tmp1 ; Save it for later
jsr READST
and #$BF
bne @L4
lda tmp1
ldy #0
sta (ptr2),y ; Save read byte
inc ptr2
bne @L2
inc ptr2+1 ; ++buffer;
@L2: inc ptr3
bne @L3
inc ptr3+1 ; ++bytesread;
@L3: dec ptr1
bne @L1
dec ptr1+1
bne @L1
@L4: jsr CLRCH
lda ptr3
ldx ptr3+1 ; return bytesread;
rts
; CHKIN failed
@E1: sta ___oserror
lda #$FF
tax
rts ; return -1