Sun, 16 Apr 1995 19:13:50 GMT

Related articles |
---|

[3 earlier articles] |

Re: Q: division vs multiplication mikeq@primenet.com (1995-04-02) |

Re: Q: division vs multiplication hbaker@netcom.com (1995-04-03) |

Re: Q: division vs multiplication davidm@Rational.COM (1995-04-03) |

Re: Q: division vs multiplication brandis@inf.ethz.ch (1995-04-04) |

Re: Q: division vs multiplication Terje.Mathisen@hda.hydro.com (1995-04-06) |

Re: Q: division vs multiplication meissner@cygnus.com (Mike Meissner) (1995-04-16) |

Re: Q: division vs multiplication martens@cis.ohio-state.edu (1995-04-16) |

Re: Q: division vs multiplication jmccarty@spdmail.spd.dsccc.com (1995-04-18) |

Re: Q: division vs multiplication leichter@zodiac.rutgers.edu (1995-04-11) |

Re: Q: division vs multiplication kptben@aol.com (1995-04-17) |

Re: Q: division vs multiplication pcg@aber.ac.uk (1995-04-17) |

Re: Q: division vs multiplication gsc@magna.com.au (1995-04-18) |

Re: Q: division vs multiplication jbuck@Synopsys.COM (1995-04-28) |

[4 later articles] |

Newsgroups: | comp.compilers |

From: | martens@cis.ohio-state.edu (Jeff Martens) |

Keywords: | arithmetic, optimize |

Organization: | Hood College Dept. of Math and CS |

References: | 95-04-003 95-04-039 |

Date: | Sun, 16 Apr 1995 19:13:50 GMT |

*>t.hulek@imperial.ac.uk (Mr Tomas Hulek) wrote:*

*>[Can one optimize floating division by powers of two into something like a*

*>shift?]*

kptben@aol.com (KPT Ben) writes:

*>When using 32-bit integer math on the PowerPC 601, a brute-force divide is*

*>36 cycles; a multiply is 5 cycles, and bitshifts are 1 cycle.*

*>Multiplication and division by powers of two can be done with a single*

*>bitshift instruction on the 601 (two instructions are necessary when*

*>dividing a signed integer by a power of 2).*

You have to be careful here, though, because a right arithmetic

shift of an odd negative integer will not give the same result as

division by 2. For example:

-1 div 2 is 0

ashr(-1) is -1

--

-- Jeff (jmartens@nimue.hood.edu)

--

Post a followup to this message

Return to the
comp.compilers page.

Search the
comp.compilers archives again.