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;
; Ullrich von Bassewitz, 31.05.1998
; Christian Krueger: 12-Aug-2013, minor optimizations
;
; char* strncat (char* dest, const char* src, size_t n);
;
.export _strncat
.import popax, popptr1
.importzp ptr1, ptr2, ptr3, tmp1, tmp2
.macpack cpu
_strncat:
eor #$FF ; one's complement to count upwards
sta tmp1
txa
eor #$FF
sta tmp2
jsr popptr1 ; get src
jsr popax ; get dest
sta ptr3 ; remember for function return
stx ptr3+1
stx ptr2+1
tay ; low byte as offset in Y
.if (.cpu .bitand ::CPU_ISET_65SC02)
stz ptr2
.else
ldx #0
stx ptr2 ; destination on page boundary
.endif
; find end of dest
L1: lda (ptr2),y
beq L2
iny
bne L1
inc ptr2+1
bne L1
; end found, apply offset to dest ptr and reset y
L2: sty ptr2
; 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
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