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libsrc/runtime/add.s

@@ -0,0 +1,47 @@
+;
+; Ullrich von Bassewitz, 05.08.1998
+;
+; CC65 runtime: add ints
+;
+
+; Make this as fast as possible, even if it needs more space since it's
+; called a lot!
+
+       	.export		tosadda0, tosaddax
+	.importzp	sp, tmp1
+
+tosadda0:
+	ldx	#0
+tosaddax:
+	ldy	#0
+	clc
+	adc	(sp),y		; lo byte
+	sta	tmp1		; save it
+	txa
+	iny
+	adc	(sp),y		; hi byte
+	tax
+	clc
+	lda	sp
+	adc	#2
+	sta	sp
+	bcc	L1
+	inc	sp+1
+L1:	txa	    		; Test high byte
+	bmi	L2
+	bne	L3
+	lda	tmp1		; Get low byte
+	rts
+
+; Value is negative
+
+L2:	lda	tmp1		; Get low byte
+	ldy	#$FF		; Force negative
+	rts
+
+; Value is positive != 0
+
+L3:	lda	tmp1		; Get low byte
+	ldy	#1
+	rts
+