Sat, 14 Oct 1995 10:18:15 GMT

Related articles |
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Faster divides sdenman@wolf.cs.washington.edu (1995-10-14) |

Re: Faster divides idr@cs.pdx.edu (1995-10-23) |

Re: Faster divides cdg@nullstone.com (1995-10-25) |

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!

Thanks for any help you can offer,

Stuart Denman

sdenman@cs.washington.edu

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