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99 lines
1.5 KiB
ArmAsm
99 lines
1.5 KiB
ArmAsm
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; Ullrich von Bassewitz, 31.05.1998
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;
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; char* 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, ptr3, tmp1, tmp2
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_strncpy:
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sta tmp1 ; Save size
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stx tmp2
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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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sta ptr3 ; remember for function return
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stx ptr3+1
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ldy #$00
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ldx tmp1 ; Low byte of size
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beq L1
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; Copy the first chunk < 256
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jsr CopyChunk
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bcs L3 ; Jump if end of string found
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; Copy full 256 byte chunks
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L1: lda tmp2 ; High byte of size
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beq L3
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ldx #$00 ; Copy 256 bytes
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L2: jsr CopyChunk
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bcs L3
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dec tmp2
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bne L2
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beq L9
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; Fill the remaining space with zeroes. If we come here, the value in X
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; is the low byte of the fill count, tmp2 holds the high byte. Y is the index
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; into the target string.
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L3: tax ; Test low byte
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beq L4
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jsr FillChunk
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L4: lda tmp2 ; Test high byte
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beq L9
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L5: jsr FillChunk
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dec tmp2
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bne L5
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; Done - return a pointer to the string
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L9: lda ptr3
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ldx ptr3+1
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rts
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; -------------------------------------------------------------------
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; Copy byte count in X from ptr1 to ptr2
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.proc CopyChunk
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L1: lda (ptr1),y
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sta (ptr2),y
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beq L3
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iny
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bne L2
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inc ptr1+1
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inc ptr2+1
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L2: dex
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bne L1
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clc
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rts
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L3: sec
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rts
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.endproc
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; -------------------------------------------------------------------
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; Fill byte count in X with zeroes
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.proc FillChunk
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lda #$00
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L1: sta (ptr1),y
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iny
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bne L2
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inc ptr1+1
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L2: dex
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bne L1
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rts
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.endproc
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