16 Mar 1997 23:05:12 -0500

Related articles |
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Multiplication by a constant - how? Sergey.Solyanik@bentley.com (Sergey Solyanik) (1997-03-14) |

Re: Multiplication by a constant - how? rweaver@ix.netcom.com (1997-03-16) |

Re: Multiplication by a constant - how? harwood@trinidad.progress.com (1997-03-16) |

Re: Multiplication by a constant - how? d.sand@ix.netcom.com (Duane Sand) (1997-03-16) |

Re: Multiplication by a constant - how? harwood@trinidad.progress.com (1997-03-16) |

Re: Multiplication by a constant - how? dlmoore@ix.netcom.com (David L Moore) (1997-03-16) |

Re: Multiplication by a constant - how? preston@tera.com (1997-03-21) |

Re: Multiplication by a constant - how? torbenm@diku.dk (1997-03-21) |

[3 later articles] |

From: | rweaver@ix.netcom.com (Richard Weaver ) |

Newsgroups: | comp.compilers |

Date: | 16 Mar 1997 23:05:12 -0500 |

Organization: | Netcom |

References: | 97-03-062 |

Keywords: | arithmetic, optimize |

Sergey Solyanik <Sergey.Solyanik@bentley.com> writes:

*>MicroSoft Visual C seems to be capable to generate multiplication by a*

*>constant using sequence of shifts and adds no longer than 6 operations*

*>(total), using at most two registers. The optimization is used always*

*>and does not seem to be confined to any special cases. Does anybody*

*>know what algorithm is used and where can I look for information?*

...

One source for this algorithm is

Richard J. Gillings

Mathematics in the Time of the Pharaohs

MIT, 1972

Dover reprint 1982

From page 18 "When the Egyptian scribe needed to multiply two numbers,

he would first decide which would be the multiplicand, then he would

repeatedly multiply this by 2, adding up the intermediate multipliers

until they summed to the original multiplier"

Dick W

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