Talk:Programming:Integer Multiplication
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Revision as of 19:42, 6 May 2007 by Executioner (Talk | contribs) (New page: The FastMult routine using logs can be optimised somewhat from it's original by removing the slow SET instructions and extra direct addressing operation: <pre> FastMult: ld l,c l...)
The FastMult routine using logs can be optimised somewhat from it's original by removing the slow SET instructions and extra direct addressing operation:
FastMult: ld l,c ld h,&82 ld d,(hl) ; d = 32 * log_2(c) ld l,b ld a,(hl) ; a = 32 * log_2(b) add a,d ld l,a ld a,0 adc a,0 ld h,a ; hl = d + a add hl,hl set 2,h ; hl = hl + $0400 set 7,h ; hl = hl + &8000 ld e,(hl) inc hl ld d,(hl) ; de = 2^((hl)/32) ret
to
FastMult: ld l,c ld h,&82 ld d,(hl) ; d = 32 * log_2(c) ld l,b ld a,(hl) ; a = 32 * log_2(b) add a,d ld l,a adc &42 sub l ld h,a ; hl = d + a add hl,hl ld e,(hl) inc l ld d,(hl) ; de = 2^((hl)/32) ret
The add hl,hl can also be removed if the tables are split with low-byte in one page and high-byte in the other.
