android / kernel / msm / 68cdc8df1cb6622980b791ce03e99c255c9888af / . / include / linux / reciprocal_div.h

#ifndef _LINUX_RECIPROCAL_DIV_H | |

#define _LINUX_RECIPROCAL_DIV_H | |

#include <linux/types.h> | |

/* | |

* This file describes reciprocical division. | |

* | |

* This optimizes the (A/B) problem, when A and B are two u32 | |

* and B is a known value (but not known at compile time) | |

* | |

* The math principle used is : | |

* Let RECIPROCAL_VALUE(B) be (((1LL << 32) + (B - 1))/ B) | |

* Then A / B = (u32)(((u64)(A) * (R)) >> 32) | |

* | |

* This replaces a divide by a multiply (and a shift), and | |

* is generally less expensive in CPU cycles. | |

*/ | |

/* | |

* Computes the reciprocal value (R) for the value B of the divisor. | |

* Should not be called before each reciprocal_divide(), | |

* or else the performance is slower than a normal divide. | |

*/ | |

extern u32 reciprocal_value(u32 B); | |

static inline u32 reciprocal_divide(u32 A, u32 R) | |

{ | |

return (u32)(((u64)A * R) >> 32); | |

} | |

#endif |