16 May 1999 15:26:59 -0400

Related articles |
---|

Rounding with Div and Mod operators william.rayer@virgin.net (William Rayer) (1999-05-09) |

Re: Rounding with Div and Mod operators wclodius@aol.com (1999-05-16) |

Re: Rounding with Div and Mod operators ucapjab@ucl.ac.uk (Jonathan Barker) (1999-05-16) |

Re: Rounding with Div and Mod operators nr@labrador.cs.virginia.edu (Norman Ramsey) (1999-05-16) |

Re: Rounding with Div and Mod operators guerby@acm.org (Laurent Guerby) (1999-05-16) |

Re: Rounding with Div and Mod operators anton@mips.complang.tuwien.ac.at (1999-05-16) |

Re: Rounding with Div and Mod operators Scott.Daniels@Acm.Org (Scott.David.Daniels) (1999-05-16) |

Re: Rounding with Div and Mod operators cdg@nullstone.com (Christopher Glaeser) (1999-05-16) |

Re: Rounding with Div and Mod operators johan.persson@mbox319.swipnet.se (Johan Persson) (1999-05-16) |

Re: Rounding with Div and Mod operators genew@shuswap.net (1999-05-20) |

Re: Rounding with Div and Mod operators sofkam@rpi.edu (1999-05-20) |

Re: Rounding with Div and Mod operators drh@microsoft.com (Dave Hanson) (1999-05-20) |

Re: Rounding with Div and Mod operators anton@mips.complang.tuwien.ac.at (1999-05-20) |

Re: Rounding with Div and Mod operators peter.r.wilson@boeing.com (Peter Wilson) (1999-05-20) |

[6 later articles] |

From: | Christopher Glaeser <cdg@nullstone.com> |

Newsgroups: | comp.compilers |

Date: | 16 May 1999 15:26:59 -0400 |

Organization: | Nullstone Corporation |

References: | 99-05-039 |

Keywords: | arithmetic, design |

*> What is interesting about this rule is there seem to be two ways of*

*> rounding that satisfy it when n or d are negative - either we round*

*> integers to the next lowest value or we round towards zero.*

*> My question is: which rounding system is preferred and does it matter?*

Which ever rounding direction you choose, make sure the implementation

is correct. Several years ago I looked at the integer divide code

generated by twenty commercial C compilers to fine tune our

performance test suite, and twelve of these compilers generated

incorrect code. The most common defect was related to power-of-two

optimization such that (x / 2) generated different results than (x /

y) when y=2.

Best,

Christopher Glaeser mailto:cdg@nullstone.com

Nullstone Corporation http://www.nullstone.com

Post a followup to this message

Return to the
comp.compilers page.

Search the
comp.compilers archives again.