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//lib/modules/2.6.32-754.el6.x86_64/build/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