Changes
/* 16bit * 16bit Unsigned -> 32 bits result */ forgotten label
'''Output:''' HL = ''Product''
'''CPC Cycles:''' 188-244 (216 on average) = 47-61 (54) usec
'''Size:''' 33 bytes
The additional clocks and bytes maybe required to set up D and L and for RET.
<pre>
sla h ; optimised 1st iteration
add hl,de ; ...
</pre>
== Classic 16bit * 8bit Unsigned ==
'''Output:''' A:HL = ''Product''
'''CPC Cycles:''' 212-300 (256 on average) = 53-75 (64) usec
'''Size:''' 47 bytes
<pre>
adc a,c ; ...
</pre>
== Fast 8bit * 8bit Unsigned (using log / antilog tables) ==
'''Output:''' DE = ''Product''
'''CPC Cycles:''' 124 = 31 usec
'''Size:''' 1024 bytes (768 bytes for the tables)
'''Warning:''' It is VERY approximate routine, e.g., 0*7=7, 1*28=27, 10*81=790, 100*100=9742, ...
<pre>
</pre>
== FasterFastest, accurate 8bit * 8bit Unsigned with 16 KB tables == '''Input:''' L = Multiplier, C = Multiplicand '''Output:''' DE = Product '''CPC Cycles:''' 80 = 20 usec '''Size:''' 14 bytes of code + 16 KB tables
I'm currently working on a new routine, based on a routine by Kirk Meyer [http://www.ticalc.org/pub/86/asm/source/routines/vfmult.asm] which uses nibble multiplication tables.
ld d,a ; 20
</pre>
== Fast, accurate 8bit * 8bit Unsigned with 8 KB tables ==
'''Input:''' L = Multiplier, C = Multiplicand
'''Output:''' DE = Product
'''CPC Cycles:''' 100 = 25 usec
'''Size:''' 19 bytes of code + 8 KB tables
16K is a lot of memory to use for tables, but I'm working on a way to reduce this to 8K while maintaining similar performance (around 26μs). The idea is rather than using tables for the low and high nibbles, use tables for alternate bits. So there would be 16 tables for the values #00, #01, #04, #05, #10, #11, #14, #15, #40, #41, #44, #45, #50, #51, #54, #55. The values can be shifted by 1 (rather than 4) to give values for the alternate bits using a simple ADD HL,HL.
</pre>
== 16bit Very fast 8bit * 16bit 8bit Unsigned with only 1K of tables ==
'''Input:''' BC A = ''Multiplier'', DE L = ''Multiplicand''
'''Output:''' A,HL DE = ''Product'' '''CPC Cycles''': 104-112 (108 on average) = 26-28 (27) usec '''Size''': 24 bytes of code and 1024 bytes for the tables Here's a new routine I've developed which uses the formula ab = ((a + b)<sup>2</sup> - (a - b)<sup>2</sup>) / 4. It's based on a routine for the 6502 by Stephen Judd in a C= Hacking article. Because of differences between the way the 6502 does register indexing it was quite difficult to actually get this working, but it's a great compromise between speed and space since it only uses 1K of tables (as opposed to the 16K or 8K table routines above), and can still manage to do the job in a maximum of 28 microseconds. <br>Firstly, once again, we need some code to generate the tables. These tables contain values for <br>x<sup>2</sup>/4 for 9 bit values of x, with the LSB when bit 8 is zero first followed by the MSB.<pre>.gen_sq4 xor a ld de,umul_tab + #1ff ld (de),a dec d ld (de),a ld h,d ld l,e inc e ld c,e ld b,2 .sq4_lp ld a,b cp 2 ld a,e rra add (hl) ld (de),a inc h inc d ld a,(hl) adc c ld (de),a dec d ld h,d inc l inc e jr nz,sq4_lp inc d inc d djnz sq4_lp ret align #100.umul_tab ds #400 </pre>Now for the actual multiply routine:
<pre>
ld h,umul_tab_lo / #100 ; 2 ld b,h ; 3 add l ; 4 ld c,a ; 5 jr nc,@noovf ; 7 inc b ; 8 inc b ; 9.@noovf sub l ; 10 sub l ; 11 jr nc,@noneg ; 13 neg ; 15.@noneg ld l,a ; 16 ld a,(bc) ; 18 sub (hl) ; 20 ld e,a ; 21 inc b ; 22 inc h ; 23 ld a,(bc) ; 25 sbc (hl) ; 27 ld d,a ; 28 </pre>This code could easily be converted to a macro as it's only 24 bytes. I've tried to optimize it further but with no luck! [[User:Executioner|Executioner]] 06:25, 4 April 2008 (CEST) == Fast 8bit * 8bit Unsigned with only 512 bytes of tables == '''Input''': A = Multiplier, B = Multiplicant '''Output''': A:E = Product '''CPC Cycles''': 136-172 (154 on average) = 34-43 (38.5) usec '''Size''': 44 bytes of code and 512 bytes for the tables Fast 8 bit unsigned multiplication with 16 bit result. It uses formula<br>x*y = ((x+y)/2)<sup>2</sup> - ((x-y)/2)<sup>2</sup>, if x+y is even<br> = ((x+y-1)/2)<sup>2</sup> - ((x-y-1)/2)<sup>2</sup> + y, if x+y is odd and x>=y <pre> cp b jr nc,l1 ld e,a ld a,b ld b,e l1 ld c,a sub b rra ld d,a ld a,c add a,b rra ld l,a ld h,high(sqrlo) ld a,(hl) ld e,l ld l,d jr nc,l2 sub (hl) ;odd ld l,e ld e,a inc h ;loads high(sqrhi) ld a,(hl) ld l,d sbc a,(hl) ld d,a ld a,e add a,b ld e,a ld a,d adc a,0 ret l2 sub (hl) ;even ld l,e ld e,a inc h ld a,(hl) ld l,d sbc a,(hl) ret sqrlo ;low(x*x) should be at the page border db 0,1,4,9,$10,$19,$24,$31,$40,$51,$64,$79,$90,$a9,$c4,$e1 db 0,$21,$44,$69,$90,$b9,$e4,$11,$40,$71,$a4,$d9,$10,$49,$84,$c1 db 0,$41,$84,$c9,$10,$59,$a4,$f1,$40,$91,$e4,$39,$90,$e9,$44,$a1 db 0,$61,$c4,$29,$90,$f9,$64,$d1,$40,$b1,$24,$99,$10,$89,4,$81 db 0,$81,4,$89,$10,$99,$24,$b1,$40,$d1,$64,$f9,$90,$29,$c4,$61 db 0,$a1,$44,$e9,$90,$39,$e4,$91,$40,$f1,$a4,$59,$10,$c9,$84,$41 db 0,$c1,$84,$49,$10,$d9,$a4,$71,$40,$11,$e4,$b9,$90,$69,$44,$21 db 0,$e1,$c4,$a9,$90,$79,$64,$51,$40,$31,$24,$19,$10,9,4,$1 db 0,1,4,9,$10,$19,$24,$31,$40,$51,$64,$79,$90,$a9,$c4,$e1 db 0,$21,$44,$69,$90,$b9,$e4,$11,$40,$71,$a4,$d9,$10,$49,$84,$c1 db 0,$41,$84,$c9,$10,$59,$a4,$f1,$40,$91,$e4,$39,$90,$e9,$44,$a1 db 0,$61,$c4,$29,$90,$f9,$64,$d1,$40,$b1,$24,$99,$10,$89,4,$81 db 0,$81,4,$89,$10,$99,$24,$b1,$40,$d1,$64,$f9,$90,$29,$c4,$61 db 0,$a1,$44,$e9,$90,$39,$e4,$91,$40,$f1,$a4,$59,$10,$c9,$84,$41 db 0,$c1,$84,$49,$10,$d9,$a4,$71,$40,$11,$e4,$b9,$90,$69,$44,$21 db 0,$e1,$c4,$a9,$90,$79,$64,$51,$40,$31,$24,$19,$10,9,4,$1sqrhi ;high(x*x) db 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 db 1,1,1,1,1,1,1,2,2,2,2,2,3,3,3,3 db 4,4,4,4,5,5,5,5,6,6,6,7,7,7,8,8 db 9,9,9,$a,$a,$a,$b,$b,$c,$c,$d,$d,$e,$e,$f,$f db $10,$10,$11,$11,$12,$12,$13,$13,$14,$14,$15,$15,$16,$17,$17,$18 db $19,$19,$1a,$1a,$1b,$1c,$1c,$1d,$1e,$1e,$1f,$20,$21,$21,$22,$23 db $24,$24,$25,$26,$27,$27,$28,$29,$2a,$2b,$2b,$2c,$2d,$2e,$2f,$30 db $31,$31,$32,$33,$34,$35,$36,$37,$38,$39,$3a,$3b,$3c,$3d,$3e,$3f db $40,$41,$42,$43,$44,$45,$46,$47,$48,$49,$4a,$4b,$4c,$4d,$4e,$4f db $51,$52,$53,$54,$55,$56,$57,$59,$5a,$5b,$5c,$5d,$5f,$60,$61,$62 db $64,$65,$66,$67,$69,$6a,$6b,$6c,$6e,$6f,$70,$72,$73,$74,$76,$77 db $79,$7a,$7b,$7d,$7e,$7f,$81,$82,$84,$85,$87,$88,$8a,$8b,$8d,$8e db $90,$91,$93,$94,$96,$97,$99,$9a,$9c,$9d,$9f,$a0,$a2,$a4,$a5,$a7 db $a9,$aa,$ac,$ad,$af,$b1,$b2,$b4,$b6,$b7,$b9,$bb,$bd,$be,$c0,$c2 db $c4,$c5,$c7,$c9,$cb,$cc,$ce,$d0,$d2,$d4,$d5,$d7,$d9,$db,$dd,$df db $e1,$e2,$e4,$e6,$e8,$ea,$ec,$ee,$f0,$f2,$f4,$f6,$f8,$fa,$fc,$fe</pre> [[User:Litwr|Litwr]] 10:25, 24 October 2015 (CEST) == 16bit * 16bit Unsigned -> 32 bits result == '''Input:''' BC = ''Multiplier'', DE = ''Multiplicand'' '''Output:''' DE,HL = ''Product''<pre>ld hl,0ld a,16muluw add hl,hl rl e rl d jr nc,muluw_cont add hl,bc jr nc,muluw_cont inc demuluw_cont dec a jr nz,muluw</pre> == 16bit * 16bit Unsigned -> 24 bits result == '''Input:''' BC = ''Multiplier'', DE = ''Multiplicand'' '''Output:''' A,HL = ''Product''<pre>ld ix,0
ld hl,0
.mul24b1:
db #dd:ld d,h
ex de,hl
ret</pre>
== Web links ==
* [http://map.tni.nl/articles/mult_div_shifts.php Multiplications and divisions on the MSX Assembly Page]
* [http://www.mccw.hetlab.tk/92/Multiplication/en.html "Multiplication on a Z80" ( MSX Computer & Club Webmagazine)]
* [http://www.andreadrian.de/oldcpu/Z80_number_cruncher.html The Z80 number cruncher (Andre Adrian)] (16/32bit multiplication, addition, right shift)
[[Category:Programming]]
