1 #ifndef _LINUX_RECIPROCAL_DIV_WRAPPER_H
2 #define _LINUX_RECIPROCAL_DIV_WRAPPER_H 1
4 #include <linux/types.h>
7 * This algorithm is based on the paper "Division by Invariant
8 * Integers Using Multiplication" by Torbjörn Granlund and Peter
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
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.
22 #define reciprocal_value rpl_reciprocal_value
23 struct reciprocal_value {
28 struct reciprocal_value reciprocal_value(u32 d);
30 #define reciprocal_divide rpl_reciprocal_divide
31 static inline u32 reciprocal_divide(u32 a, struct reciprocal_value R)
33 u32 t = (u32)(((u64)a * R.m) >> 32);
34 return (t + ((a - t) >> R.sh1)) >> R.sh2;
37 #endif /* _LINUX_RECIPROCAL_DIV_WRAPPER_H */