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git.proxmox.com Git - mirror_ubuntu-eoan-kernel.git/blob - include/linux/reciprocal_div.h
1 #ifndef _LINUX_RECIPROCAL_DIV_H
2 #define _LINUX_RECIPROCAL_DIV_H
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 struct reciprocal_value
{
27 struct reciprocal_value
reciprocal_value(u32 d
);
29 static inline u32
reciprocal_divide(u32 a
, struct reciprocal_value R
)
31 u32 t
= (u32
)(((u64
)a
* R
.m
) >> 32);
32 return (t
+ ((a
- t
) >> R
.sh1
)) >> R
.sh2
;
35 #endif /* _LINUX_RECIPROCAL_DIV_H */