Sun, 2 Apr 1995 13:50:23 GMT

Related articles |
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Q: division vs multiplication t.hulek@imperial.ac.uk (1995-03-24) |

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

Re: Q: division vs multiplication Terje.Mathisen@hda.hydro.com (1995-04-02) |

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) |

[9 later articles] |

Newsgroups: | comp.compilers |

From: | mikeq@primenet.com (Michael Quinlan) |

Keywords: | arithmetic, optimize |

Organization: | Primenet |

References: | 95-04-003 |

Date: | Sun, 2 Apr 1995 13:50:23 GMT |

t.hulek@imperial.ac.uk (Mr Tomas Hulek) writes:

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

shift?]

*>I would imagine that division by 2.0 could be done very efficiently, just like*

*>division by 10 in our decimal system. But is it really so?*

On at least one set of machines (the IBM System 370/390 series), division

of a floating point number by 2 is significantly faster than multiplication

because the hardware has a special instruction for it.

Of course, in a C program, division by 2 will only be faster when the

compiler detects the situation and generates code using the instruction.

A well-written compiler might detect both situations above and generate

identical code.

+---------------------------------+

| Michael Quinlan |

| mikeq@primenet.com |

| http://www.primenet.com/~mikeq/ |

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