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Div Mod
Overview
Division algorithms differ in terms of the width of the operands and results. The algorithms on this page are classified by the bit-width of these. For the operations A / B = C (Division) and A % B = D (Modulo), the algorithms are classified as "A / B = C, D".
All of these algorithms contain a loop which can be unrolled to increase speed at the expense of code size.
Unsigned "8 / 8 = 8, 8" bit
; Integer divides D by E
; Result in D, remainder in A
; Clobbers F, B
xor a
ld b,8
-: sla d
rla
cp e
jr c,+
sub e
inc d
+: djnz -
; Result in D, remainder in A
; Clobbers F, B
xor a
ld b,8
-: sla d
rla
cp e
jr c,+
sub e
inc d
+: djnz -
Unsigned "16 / 8 = 8, 8" bit
; Integer divides HL by E
; Result in A, remainder in H
; Clobbers F, B, L
ld b,8
-: adc hl,hl
ld a,h
jr c,+
cp e
jr c,++
+: sub e
ld h,a
or a
++: djnz -
ld a,l
rla
cpl
; Result in A, remainder in H
; Clobbers F, B, L
ld b,8
-: adc hl,hl
ld a,h
jr c,+
cp e
jr c,++
+: sub e
ld h,a
or a
++: djnz -
ld a,l
rla
cpl
Unsigned "16 / 8 = 16, 8" bit
; Integer divides HL by C
; Result in HL, remainder in A
; Clobbers F, B
xor a
ld b,16
-: add hl,hl
rla
cp c
jr c,+
sub c
inc l
+: djnz -
; Result in HL, remainder in A
; Clobbers F, B
xor a
ld b,16
-: add hl,hl
rla
cp c
jr c,+
sub c
inc l
+: djnz -
Unsigned "16 / 16 = 16, 16" bit
; Integer divides A:C by DE
; Result in A:C, remainder in HL
; Clobbers F, B
ld hl,$0000
ld b,16
-: sll c
rla
adc hl,hl
sbc hl,de
jr nc,+
add hl,de
dec c
+: djnz -
; Result in A:C, remainder in HL
; Clobbers F, B
ld hl,$0000
ld b,16
-: sll c
rla
adc hl,hl
sbc hl,de
jr nc,+
add hl,de
dec c
+: djnz -
Unsigned "24 / 8 = 24, 8" bit
; Integer divides E:HL by D
; Result in E:HL, remainder in A
; Clobbers F, B
xor a
ld b,24
-: add hl,hl
rl e
rla
cp d
jr c,+
sub d
inc l
+: djnz -
; Result in E:HL, remainder in A
; Clobbers F, B
xor a
ld b,24
-: add hl,hl
rl e
rla
cp d
jr c,+
sub d
inc l
+: djnz -
Unsigned "24 / 16 = 24, 16" bit
; Integer divides A:BC by DE
; Result in A:BC, remainder in HL
; Clobbers F, IYH
ld hl,$0000
ld iyh,24
-: sll c
rl b
rla
adc hl,hl
sbc hl,de
jr nc,+
add hl,de
dec c
+: dec iyh
jp nz,-
; Result in A:BC, remainder in HL
; Clobbers F, IYH
ld hl,$0000
ld iyh,24
-: sll c
rl b
rla
adc hl,hl
sbc hl,de
jr nc,+
add hl,de
dec c
+: dec iyh
jp nz,-
Unsigned "32 / 8 = 32, 8" bit
; Integer divides DE:HL by C
; Result in DE:HL, remainder in A
; Clobbers F, B
xor a
ld b,32
-: add hl,hl
rl e
rl d
rla
cp c
jr c,+
sub c
inc l
+: djnz -
; Result in DE:HL, remainder in A
; Clobbers F, B
xor a
ld b,32
-: add hl,hl
rl e
rl d
rla
cp c
jr c,+
sub c
inc l
+: djnz -
Unsigned "32 / 16 = 16, 16" bit
; Integer divides HLBC by DE, returns result in BC and remainder in HL
; Clobbers A, F, IYH
; Found on Usenet
Divide16:
ld iyh,16
-: rl c
rl b
adc hl,hl
sbc a,a
or a
sbc hl,de
sbc a,0
jr nc,+
add hl,de
scf
+: dec iyh
jp nz,-
rl c
rl b
ld a,c
cpl
ld c,a
ld a,b
cpl
ld b,a
ret
; Clobbers A, F, IYH
; Found on Usenet
Divide16:
ld iyh,16
-: rl c
rl b
adc hl,hl
sbc a,a
or a
sbc hl,de
sbc a,0
jr nc,+
add hl,de
scf
+: dec iyh
jp nz,-
rl c
rl b
ld a,c
cpl
ld c,a
ld a,b
cpl
ld b,a
ret
Z80 Bits
See also http://baze.au.com/misc/z80bits.html
TODO
Use Meka's CLOCK and/or a test framework to get some timing data.
