1 #ifndef _LINUX_RECIPROCAL_DIV_H 2 #define _LINUX_RECIPROCAL_DIV_H 3 4 #include <linux/types.h> 5 6 /* 7 * This algorithm is based on the paper "Division by Invariant 8 * Integers Using Multiplication" by Torbjörn Granlund and Peter 9 * L. Montgomery. 10 * 11 * The assembler implementation from Agner Fog, which this code is 12 * based on, can be found here: 13 * http://www.agner.org/optimize/asmlib.zip 14 * 15 * This optimization for A/B is helpful if the divisor B is mostly 16 * runtime invariant. The reciprocal of B is calculated in the 17 * slow-path with reciprocal_value(). The fast-path can then just use 18 * a much faster multiplication operation with a variable dividend A 19 * to calculate the division A/B. 20 */ 21 22 struct reciprocal_value { 23 u32 m; 24 u8 sh1, sh2; 25 }; 26 27 struct reciprocal_value reciprocal_value(u32 d); 28 reciprocal_divide(u32 a,struct reciprocal_value R)29static inline u32 reciprocal_divide(u32 a, struct reciprocal_value R) 30 { 31 u32 t = (u32)(((u64)a * R.m) >> 32); 32 return (t + ((a - t) >> R.sh1)) >> R.sh2; 33 } 34 35 #endif /* _LINUX_RECIPROCAL_DIV_H */ 36