From c4763e9007ba56977e75bdfc33559d81cdbdcbd3 Mon Sep 17 00:00:00 2001
From: uz <uz@b7a2c559-68d2-44c3-8de9-860c34a00d81>
Date: Wed, 19 Aug 2009 14:51:16 +0000
Subject: [PATCH] Special cased the division 16 by 8.

git-svn-id: svn://svn.cc65.org/cc65/trunk@4043 b7a2c559-68d2-44c3-8de9-860c34a00d81
---
 libsrc/runtime/udiv.s | 60 +++++++++++++++++++++++++++++++++----------
 1 file changed, 46 insertions(+), 14 deletions(-)

diff --git a/libsrc/runtime/udiv.s b/libsrc/runtime/udiv.s
index e82d5bf21..03151f94c 100644
--- a/libsrc/runtime/udiv.s
+++ b/libsrc/runtime/udiv.s
@@ -5,11 +5,12 @@
 ;
 
        	.export		tosudiva0, tosudivax, udiv16
-	.import		popsreg
-	.importzp	sreg, ptr1, ptr4
+ 	.import		popsreg
+ 	.importzp	sreg, ptr1, ptr4
+
 
 tosudiva0:
-       	ldx	#0
+        ldx     #$00            ; Clear high byte
 tosudivax:
        	sta	ptr4
        	stx	ptr4+1 	       	; Save right operand
@@ -25,30 +26,61 @@ tosudivax:
  	ldx	sreg+1
  	rts
 
-; Do (sreg/ptr4) -> sreg (see mult-div.s from "The Fridge").
+;---------------------------------------------------------------------------
+; 16by16 division. Divide sreg by ptr4. Result is in sreg, remainder in ptr1
+; (see mult-div.s from "The Fridge").
 ; This is also the entry point for the signed division
 
 udiv16:	lda	#0
  	sta	ptr1+1
  	ldy	#16
+        ldx     sreg+1
+        beq     udiv16by8a
+
 L0:	asl	sreg
  	rol	sreg+1
  	rol	a
  	rol	ptr1+1
+
  	pha
  	cmp	ptr4
  	lda	ptr1+1
  	sbc	ptr4+1
-	bcc	L1
-	sta	ptr1+1
-	pla
-	sbc	ptr4
-	pha
-	inc	sreg
+ 	bcc	L1
+
+ 	sta	ptr1+1
+ 	pla
+ 	sbc	ptr4
+ 	pha
+ 	inc	sreg
+
 L1:	pla
-	dey
-	bne	L0
-	sta	ptr1
-	rts
+ 	dey
+ 	bne	L0
+ 	sta	ptr1
+ 	rts
 
 
+;---------------------------------------------------------------------------
+; 16by8 division
+
+udiv16by8:
+        lda	#0
+ 	sta	ptr1+1
+ 	ldy	#16
+udiv16by8a:
+@L0:	asl	sreg
+  	rol	sreg+1
+  	rol	a
+        bcs     @L1
+
+   	cmp	ptr4
+    	bcc	@L2
+@L1:    sbc	ptr4
+    	inc	sreg
+
+@L2:	dey
+    	bne    	@L0
+    	sta    	ptr1
+    	rts
+