;
-; Ullrich von Bassewitz, 31.05.1998
+; Ullrich von Bassewitz, 2003-05-04
;
-; char* strncpy (char* dest, const char* src, unsigned size);
+; char* __fastcall__ strncpy (char* dest, const char* src, unsigned size);
;
- .export _strncpy
- .import popax
- .importzp ptr1, ptr2, ptr3, tmp1, tmp2
+ .export _strncpy
+ .import popax
+ .importzp ptr1, ptr2, tmp1, tmp2, tmp3
+
+.proc _strncpy
+
+ eor #$FF
+ sta tmp1
+ txa
+ eor #$FF
+ sta tmp2 ; Store -size - 1
-_strncpy:
- sta tmp1 ; Save size
- stx 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
+ stx tmp3 ; remember for function return
+
+; Copy src -> dest up to size bytes
+ ldx tmp1 ; Load low byte of ones complement of size
ldy #$00
- ldx tmp1 ; Low byte of size
- beq L1
-
-; Copy the first chunk < 256
-
- jsr CopyChunk
- bcs L3 ; Jump if end of string found
-
-; Copy full 256 byte chunks
-
-L1: lda tmp2 ; High byte of size
- beq L3
- ldx #$00 ; Copy 256 bytes
-L2: jsr CopyChunk
- bcs L3
- dec tmp2
- bne L2
- beq L9
-
-; Fill the remaining space with zeroes. If we come here, the value in X
-; is the low byte of the fill count, tmp2 holds the high byte. Y is the index
-; into the target string.
-
-L3: tax ; Test low byte
- beq L4
- jsr FillChunk
-
-L4: lda tmp2 ; Test high byte
- beq L9
-L5: jsr FillChunk
- dec tmp2
- bne L5
-
-; Done - return a pointer to the string
-
-L9: lda ptr3
- ldx ptr3+1
- rts
-
-
-; -------------------------------------------------------------------
-; Copy byte count in X from ptr1 to ptr2
-
-.proc CopyChunk
-L1: lda (ptr1),y
- sta (ptr2),y
- beq L3
- iny
- bne L2
- inc ptr1+1
- inc ptr2+1
-L2: dex
- bne L1
- clc
- rts
-L3: sec
- rts
-.endproc
+L1: inx
+ bne L2
+ inc tmp2
+ beq L9
+
+L2: lda (ptr1),y ; Copy one character
+ sta (ptr2),y
+ beq L5 ; Bail out if terminator reached (A = 0)
+ iny
+ bne L1
+ inc ptr1+1
+ inc ptr2+1 ; Bump high bytes
+ bne L1 ; Branch always
+; Fill the remaining bytes.
-; -------------------------------------------------------------------
-; Fill byte count in X with zeroes
+L3: inx ; Counter low byte
+ beq L6 ; Branch on overflow
+L4: sta (ptr2),y ; Clear one byte
+L5: iny ; Bump pointer
+ bne L3
+ inc ptr2+1 ; Bump high byte
+ bne L3 ; Branch always
+
+; Bump the counter high byte
+
+L6: inc tmp2
+ bne L4
+
+; Done, return dest
+
+L9: lda ptr2 ; Get low byte
+ ldx tmp3 ; Get unchanged high byte
+ rts
-.proc FillChunk
- lda #$00
-L1: sta (ptr1),y
- iny
- bne L2
- inc ptr1+1
-L2: dex
- bne L1
- rts
.endproc
+