1 #ifndef _LINUX_RECIPROCAL_DIV_H 2 #define _LINUX_RECIPROCAL_DIV_H 3 4 #include <linux/types.h> 5 6 /* 7 * This file describes reciprocical division. 8 * 9 * This optimizes the (A/B) problem, when A and B are two u32 10 * and B is a known value (but not known at compile time) 11 * 12 * The math principle used is : 13 * Let RECIPROCAL_VALUE(B) be (((1LL << 32) + (B - 1))/ B) 14 * Then A / B = (u32)(((u64)(A) * (R)) >> 32) 15 * 16 * This replaces a divide by a multiply (and a shift), and 17 * is generally less expensive in CPU cycles. 18 */ 19 20 /* 21 * Computes the reciprocal value (R) for the value B of the divisor. 22 * Should not be called before each reciprocal_divide(), 23 * or else the performance is slower than a normal divide. 24 */ 25 extern u32 reciprocal_value(u32 B); 26 27 28 static inline u32 reciprocal_divide(u32 A, u32 R) 29 { 30 return (u32)(((u64)A * R) >> 32); 31 } 32 #endif 33