# Faster divides

## sdenman@wolf.cs.washington.edu (Stuart Denman)Sat, 14 Oct 1995 10:18:15 GMT

From comp.compilers

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Faster divides sdenman@wolf.cs.washington.edu (1995-10-14)
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 Newsgroups: comp.graphics.algorithms,comp.compilers From: sdenman@wolf.cs.washington.edu (Stuart Denman) Keywords: arithmetic, performance, question Organization: Computer Science & Engineering, U of Washington, Seattle Date: Sat, 14 Oct 1995 10:18:15 GMT

I remember someone saying there was a trick to speed up something like this
where you have all long variables and you divide multiple times by the same
value:

long dsh,dtx,dty,dy;
...do some calculations to find values for them...
dsh = (dsh << 16) / dy;
dtx = (dtx << 16) / dy;
dty = (dty << 16) / dy;

I tried using 3 floating-point multiplies, but that is way slower, even on
a Pentium due to the large speed hit of converting back-and-forth from
integer to floating-point.

Does anyone know of an algorithm to speed this up without having to do these
3 very similar divides? It seems like there would be one since you are
dividing by the exact same value!

Stuart Denman
sdenman@cs.washington.edu

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