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libsrc/runtime/laddeq.s

@@ -0,0 +1,53 @@
+;
+; Ullrich von Bassewitz, 07.04.2000
+;
+; CC65 runtime: += operator
+;
+; On entry, the low byte of the address of the variable to increment is
+; in ptr1, the high byte is in Y, and the increment is in eax.
+;
+
+       	.export	       	laddeq1, laddeqa, laddeq
+       	.importzp   	sreg, ptr1, tmp1
+
+
+laddeq1:
+       	lda	#$01
+
+laddeqa:
+	ldx	#$00
+	stx	sreg
+	stx	sreg+1
+
+laddeq:	sty 	ptr1+1	    	    	; Store high byte of address
+	ldy 	#$00	    	    	; Address low byte
+	clc
+
+	adc	(ptr1),y
+	sta	(ptr1),y
+       	pha			       	; Save byte 0 of result for later
+
+	iny			       	; Address byte 1
+	txa
+	adc	(ptr1),y	    	; Load byte 1
+	sta	(ptr1),y
+	tax
+
+	iny			    	; Address byte 2
+	lda	sreg
+	adc	(ptr1),y
+	sta	(ptr1),y
+	sta	sreg
+
+	iny			    	; Address byte 3
+	lda	sreg+1
+	adc	(ptr1),y
+	sta	(ptr1),y
+	sta	sreg+1
+
+	pla				; Retrieve byte 0 of result
+
+	rts				; Done
+
+
+