gem5 / testing / jenkins-gem5-prod / 631bfb6d257ed849270400cc7f6a39afdb732dff / . / src / base / intmath.cc

/* | |

* Copyright (c) 2001, 2003-2005 The Regents of The University of Michigan | |

* All rights reserved. | |

* | |

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* documentation and/or other materials provided with the distribution; | |

* neither the name of the copyright holders nor the names of its | |

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* this software without specific prior written permission. | |

* | |

* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS | |

* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT | |

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* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT | |

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* | |

* Authors: Nathan Binkert | |

* Steve Reinhardt | |

*/ | |

#include "base/intmath.hh" | |

int | |

prevPrime(int n) | |

{ | |

int decr; | |

// If the number is even, let's start with the previous odd number. | |

if (!(n & 1)) | |

--n; | |

// Lets test for divisibility by 3. Then we will be able to easily | |

// avoid numbers that are divisible by 3 in the future. | |

decr = n % 3; | |

if (decr == 0) { | |

n -= 2; | |

decr = 2; | |

} | |

else if (decr == 1) | |

decr = 4; | |

for (;;) { | |

if (isPrime(n)) | |

return n; | |

n -= decr; | |

// Toggle between 2 and 4 to prevent trying numbers that are known | |

// to be divisible by 3. | |

decr = 6 - decr; | |

} | |

} |