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cc65/libsrc/common/strncat.s
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git-svn-id: svn://svn.cc65.org/cc65/trunk@3 b7a2c559-68d2-44c3-8de9-860c34a00d81
2000-05-28 13:40:48 +00:00

73 lines
1.1 KiB
ArmAsm

;
; Ullrich von Bassewitz, 31.05.1998
;
; char* strncat (char* dest, const char* src, size_t n);
;
.export _strncat
.import popax
.importzp ptr1, ptr2, ptr3, tmp1, tmp2
_strncat:
eor #$FF ; one's complement to count upwards
sta tmp1
txa
eor #$FF
sta tmp2
jsr popax ; get src
sta ptr1
stx ptr1+1
jsr popax ; get dest
sta ptr2
stx ptr2+1
sta ptr3 ; remember for function return
stx ptr3+1
ldy #0
; find end of dest
L1: lda (ptr2),y
beq L2
iny
bne L1
inc ptr2+1
bne L1
; end found, get offset in y into pointer
L2: tya
clc
adc ptr2
sta ptr2
bcc L3
inc ptr2+1
; copy src. We've put the ones complement of the count into the counter, so
; we'll increment the counter on top of the loop
L3: ldy #0
ldx tmp1 ; low counter byte
L4: inx
bne L5
inc tmp2
beq L6 ; jump if done
L5: lda (ptr1),y
sta (ptr2),y
beq L7
iny
bne L4
inc ptr1+1
inc ptr2+1
bne L4
; done, set the trailing zero and return pointer to dest
L6: lda #0
sta (ptr2),y
L7: lda ptr3
ldx ptr3+1
rts