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70 lines
1.5 KiB
ArmAsm
70 lines
1.5 KiB
ArmAsm
;
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; Ullrich von Bassewitz, 2003-05-04
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; char* __fastcall__ strncpy (char* dest, const char* src, unsigned size);
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;
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.export _strncpy
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.import popax
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.importzp ptr1, ptr2, tmp1, tmp2, tmp3
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.proc _strncpy
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eor #$FF
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sta tmp1
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txa
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eor #$FF
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sta tmp2 ; Store -size - 1
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jsr popax ; get src
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sta ptr1
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stx ptr1+1
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jsr popax ; get dest
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sta ptr2
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stx ptr2+1
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stx tmp3 ; remember for function return
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; Copy src -> dest up to size bytes
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ldx tmp1 ; Load low byte of ones complement of size
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ldy #$00
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L1: inx
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bne L2
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inc tmp2
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beq L9
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L2: lda (ptr1),y ; Copy one character
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sta (ptr2),y
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beq L5 ; Bail out if terminator reached (A = 0)
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iny
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bne L1
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inc ptr1+1
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inc ptr2+1 ; Bump high bytes
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bne L1 ; Branch always
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; Fill the remaining bytes.
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L3: inx ; Counter low byte
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beq L6 ; Branch on overflow
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L4: sta (ptr2),y ; Clear one byte
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L5: iny ; Bump pointer
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bne L3
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inc ptr2+1 ; Bump high byte
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bne L3 ; Branch always
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; Bump the counter high byte
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L6: inc tmp2
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bne L4
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; Done, return dest
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L9: lda ptr2 ; Get low byte
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ldx tmp3 ; Get unchanged high byte
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rts
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.endproc
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