# 32x32=64

## gah@ugcs.caltech.edu (glen herrmannsfeldt)

20 Dec 2001 00:43:17 -0500

*From comp.compilers*

Related articles |

**32x32=64 ***gah@ugcs.caltech.edu* (2001-12-20) |

Re: 32x32=64 *RLWatkins@CompuServe.Com (R. L. Watkins)* (2001-12-22) |

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**From: ** | gah@ugcs.caltech.edu (glen herrmannsfeldt) |

**Newsgroups: ** | comp.compilers |

**Date: ** | 20 Dec 2001 00:43:17 -0500 |

**Organization: ** | California Institute of Technology, Pasadena |

**Summary: ** | 64 bit multiplication |

**Keywords: ** | arithmetic, comment |

**Posted-Date: ** | 20 Dec 2001 00:43:17 EST |

There is a discussion in comp.arch that wandered from its initial

discussion about typesetting to C code.

The point was made that mutliplying two 32 bit numbers, with one or

both cast to a 64 bit type, could be done using a 32 x 32 multiply

with 64 bit product instruction that many machines have. (Using the

"as if" rule)

The question, then, is do any compilers perform this optimization?

-- glen

[They sure did it for 16x16 -> 32 -John]

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