From 23f10afff46826e02e87143c2e91b914f26d981e Mon Sep 17 00:00:00 2001
From: Nick Downing <nick@ndcode.org>
Date: Fri, 14 Jun 2019 01:36:13 +1000
Subject: [PATCH] Fix bugs, working signed division

---
 sm.asm | 50 +++++++++++++++++++++++++++-----------------------
 1 file changed, 27 insertions(+), 23 deletions(-)

diff --git a/sm.asm b/sm.asm
index 856d028..c19d8f4 100644
--- a/sm.asm
+++ b/sm.asm
@@ -913,8 +913,8 @@ mul_hl_de:
 
 div_hl_de:
 	push	bc
-	ld	c,l
 divu:	ld	a,h
+	ld	c,l
 	ld	hl,0
 	call	div0
 	ld	b,a
@@ -930,7 +930,6 @@ divu:	ld	a,h
 
 div_hl_de_signed:
 	push	bc
-	ld	c,l
 	ld	a,h
 	or	a
 	ld	a,d
@@ -943,6 +942,7 @@ div_hl_de_signed:
 	; negative dividend, positive divisor
 	dec	hl			; reduces remainder by 1 (we inc later)
 	ld	a,h
+	ld	c,l
 	ld	hl,-1
 	call	div1
 	ld	b,a
@@ -959,15 +959,17 @@ div_hl_de_signed:
 	ret
 
 2$:	; positive dividend, negative divisor
+	ld	a,h
+	ld	c,l
 	ld	hl,0
-	call	div3
+	call	divn1
 	ld	b,a
 	ld	a,c
 	ld	c,b
 	call	divn
-;	inc	a
-;	jr	c,3$
-;	sbc	hl,de
+	inc	a
+	jr	c,3$
+	sbc	hl,de
 3$:	ld	d,c
 	ld	e,a
 	pop	bc
@@ -979,14 +981,15 @@ div_hl_de_signed:
 	; negative dividend, negative divisor
 	dec	hl			; reduces remainder by 1 (we inc later)
 	ld	a,h
+	ld	c,l
 	ld	hl,-1
-	call	div2
+	call	divn0
 	ld	b,a
 	ld	a,c
 	ld	c,b
 	call	divn
-;	jr	nc,5$
-;	add	hl,de
+	jr	nc,5$
+	add	hl,de
 5$:	inc	hl			; get into range divisor+1..0
 	ld	d,c
 	ld	e,a
@@ -1128,10 +1131,10 @@ div11:	add	a,a
  ;call print_crlf
 	ret
 
-; div2/3 are the same as div0/1 but carry reversed after add/subtract divisor
+; divn0/3 are the same as div0/1 but carry reversed after add/subtract divisor
 
-divn:	jr	c,div3
-div2:
+divn:	jr	c,divn1
+divn0:
  ;push af
  ;ld a,'A
  ;call print_char
@@ -1152,13 +1155,14 @@ div2:
 	ld	b,8
 	scf
 	rla
-div20:	adc	hl,hl
+divn00:	adc	hl,hl
+	or	a
 	sbc	hl,de
-	jr	c,div21
+	jr	c,divn01
 	dec	a
-	jr	div31
-div21:	add	a,a
-	djnz	div20
+	jr	divn11
+divn01:	add	a,a
+	djnz	divn00
 	dec	a
 	or	a
  ;push af
@@ -1181,7 +1185,7 @@ div21:	add	a,a
  ;call print_crlf
 	ret
 
-div3:
+divn1:
  ;push af
  ;ld a,'C
  ;call print_char
@@ -1201,13 +1205,13 @@ div3:
  ;ex de,hl
 	ld	b,8
 	add	a,a
-div30:	adc	hl,hl
+divn10:	adc	hl,hl
 	add	hl,de
-	jr	c,div31
+	jr	c,divn11
 	inc	a
-	jr	div21
-div31:	add	a,a
-	djnz	div30
+	jr	divn01
+divn11:	add	a,a
+	djnz	divn10
 	;inc	a
 	;dec	a			; compensation
 	scf
-- 
2.34.1