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libsrc/common/strncpy.s

@@ -0,0 +1,98 @@
+;
+; Ullrich von Bassewitz, 31.05.1998
+;
+; char* strncpy (char* dest, const char* src, unsigned size);
+;
+
+	.export		_strncpy
+	.import		popax
+	.importzp	ptr1, ptr2, ptr3, tmp1, tmp2
+
+_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
+
+	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
+
+
+; -------------------------------------------------------------------
+; Fill byte count in X with zeroes
+
+.proc	FillChunk
+	lda	#$00
+L1:	sta	(ptr1),y
+	iny
+	bne	L2
+   	inc	ptr1+1
+L2:	dex
+	bne	L1
+	rts
+.endproc
+
+