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Programming:Integer Multiplication

38 bytes added, 04:31, 4 April 2008
Stupid editor - disabled now
<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_lo 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:
'''Output:''' DE = ''Product''
<pre> ld h,umul_tab 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 optimise it further but with no luck!
Executioner
151
edits
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