kernel / pub / scm / linux / kernel / git / shemminger / vmbus-next / 51118697b54cc97a0d2d009cf5f976c5c99f3734 / . / include / linux / reciprocal_div.h

#ifndef _LINUX_RECIPROCAL_DIV_H | |

#define _LINUX_RECIPROCAL_DIV_H | |

#include <linux/types.h> | |

/* | |

* This algorithm is based on the paper "Division by Invariant | |

* Integers Using Multiplication" by Torbjörn Granlund and Peter | |

* L. Montgomery. | |

* | |

* The assembler implementation from Agner Fog, which this code is | |

* based on, can be found here: | |

* http://www.agner.org/optimize/asmlib.zip | |

* | |

* This optimization for A/B is helpful if the divisor B is mostly | |

* runtime invariant. The reciprocal of B is calculated in the | |

* slow-path with reciprocal_value(). The fast-path can then just use | |

* a much faster multiplication operation with a variable dividend A | |

* to calculate the division A/B. | |

*/ | |

struct reciprocal_value { | |

u32 m; | |

u8 sh1, sh2; | |

}; | |

struct reciprocal_value reciprocal_value(u32 d); | |

static inline u32 reciprocal_divide(u32 a, struct reciprocal_value R) | |

{ | |

u32 t = (u32)(((u64)a * R.m) >> 32); | |

return (t + ((a - t) >> R.sh1)) >> R.sh2; | |

} | |

#endif /* _LINUX_RECIPROCAL_DIV_H */ |