Difference between revisions of "Z80 Routines:Math:Division"

Revision as of 03:05, 15 March 2017 (view source) Jacobly (Talk | contribs) (Fixed 24/8 and 32/8.) ← Older edit		Revision as of 03:09, 15 March 2017 (view source) Jacobly (Talk | contribs) (I'm just going to assume Rounded 16/8 was also broken.) Newer edit →
Line 41:		Line 41:
	add hl, hl		add hl, hl
	rla		rla
−	jr c, $+5
	cp c		cp c
	jr c, $+4		jr c, $+4
−
	sub c		sub c
	inc l		inc l
Line 89:		Line 87:
	rl e		rl e
	rla		rla
−	jr c, $+5
	cp d		cp d
	jr c, $+4		jr c, $+4
−
	sub d		sub d
	inc l		inc l
Line 115:		Line 111:
	rl d		rl d
	rla		rla
−	jr c, $+5
	cp c		cp c
	jr c, $+4		jr c, $+4
−
	sub c		sub c
	inc l		inc l
Line 125:		Line 119:
	ret		ret
−	</nowiki>
−	== 32/16 division ==
−
−	The following routine divides acix by de and places the quotient in acix and the remainder in hl
−
−	<nowiki>
−	Div32By16:
−	; IN: ACIX=dividend, DE=divisor
−	; OUT: ACIX=quotient, DE=divisor, HL=remainder, B=0
−	ld hl,0
−	ld b,32
−	Div32By16_Loop:
−	add ix,ix
−	rl c
−	rla
−	adc hl,hl
−	jr c,Div32By16_Overflow
−	sbc hl,de
−	jr nc,Div32By16_SetBit
−	add hl,de
−	djnz Div32By16_Loop
−	ret
−	Div32By16_Overflow:
−	or a
−	sbc hl,de
−	Div32By16_SetBit:
−	.db $DD,$2C ; inc ixl, change to inc ix to avoid undocumented
−	djnz Div32By16_Loop
−	ret
	</nowiki>		</nowiki>
Line 168:		Line 133:
	add hl, hl		add hl, hl
	rla		rla
		+	jr c, $+5
	cp c		cp c
	jr c, $+4		jr c, $+4

---

Revision as of 03:09, 15 March 2017

Introduction

All these routines use the restoring division algorithm, adapted to the z80 architecture to maximize speed. They can easily be unrolled to gain some speed.

8/8 division

The following routine divides d by e and places the quotient in d and the remainder in a

div_d_e:
   xor	a
   ld	b, 8

_loop:
   sla	d
   rla
   cp	e
   jr	c, $+4
   sub	e
   inc	d
   
   djnz	_loop
   
   ret
 

16/8 division

The following routine divides hl by c and places the quotient in hl and the remainder in a

div_hl_c:
   xor	a
   ld	b, 16

_loop:
   add	hl, hl
   rla
   cp	c
   jr	c, $+4
   sub	c
   inc	l
   
   djnz	_loop
   
   ret
 

16/16 division

The following routine divides ac by de and places the quotient in ac and the remainder in hl

div_ac_de:
   ld	hl, 0
   ld	b, 16

_loop:
   sll	c
   rla
   adc	hl, hl
   sbc	hl, de
   jr	nc, $+4
   add	hl, de
   dec	c
   
   djnz	_loop
   
   ret
 

24/8 division

The following routine divides ehl by d and places the quotient in ehl and the remainder in a

div_ehl_d:
   xor	a
   ld	b, 24

_loop:
   add	hl, hl
   rl	e
   rla
   cp	d
   jr	c, $+4
   sub	d
   inc	l
   
   djnz	_loop
   
   ret
 

32/8 division

The following routine divides dehl by c and places the quotient in dehl and the remainder in a

div_dehl_c:
   xor	a
   ld	b, 32

_loop:
   add	hl, hl
   rl	e
   rl	d
   rla
   cp	c
   jr	c, $+4
   sub	c
   inc	l
   
   djnz	_loop
   
   ret
 

Rounded 16/8 division

The following routine divides hl by c and places the rounded quotient in hl and twice the prerounded remainder in a.

RoundHL_Div_C:
   xor	a
   ld	b, 16

_loop:
   add	hl, hl
   rla
   jr	c, $+5
   cp	c
   jr	c, $+4
   sub	c
   inc	l   
   djnz	_loop
;This part is the rounding
   add a,a
   cp	c
   ret	c
   inc hl
   ret