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libsrc/runtime/mul.s

@@ -0,0 +1,43 @@
+;
+; Ullrich von Bassewitz, 07.08.1998
+;
+; CC65 runtime: multiplication for ints
+;
+
+       	.export		tosumula0, tosumulax, tosmula0, tosmulax
+	.import		popsreg
+	.importzp	sreg, tmp1, ptr4
+
+tosmula0:
+tosumula0:
+	ldx	#0
+tosmulax:
+tosumulax:
+mul16:	sta	ptr4
+      	stx	ptr4+1 	       	; Save right operand
+      	jsr	popsreg	       	; Get left operand
+
+; Do ptr4*sreg --> AX (see mult-div.s from "The Fridge").
+
+	lda	#0
+   	sta	tmp1
+	ldx	sreg+1	       	; Get into register for speed
+   	ldy    	#16 	       	; Number of bits
+L0:	lsr	tmp1
+   	ror	a
+   	ror	ptr4+1
+   	ror	ptr4
+   	bcc	L1
+   	clc
+   	adc	sreg
+   	pha
+       	txa	    	       	; hi byte of left op
+   	adc	tmp1
+   	sta	tmp1
+   	pla
+L1:	dey
+       	bpl    	L0
+	lda	ptr4	       	; Load the result
+	ldx	ptr4+1
+	rts			; Done
+