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b2441318 | 1 | /* SPDX-License-Identifier: GPL-2.0 */ |
6a2d7a95 ED |
2 | #ifndef _LINUX_RECIPROCAL_DIV_H |
3 | #define _LINUX_RECIPROCAL_DIV_H | |
4 | ||
5 | #include <linux/types.h> | |
6 | ||
7 | /* | |
809fa972 HFS |
8 | * This algorithm is based on the paper "Division by Invariant |
9 | * Integers Using Multiplication" by Torbjörn Granlund and Peter | |
10 | * L. Montgomery. | |
6a2d7a95 | 11 | * |
809fa972 HFS |
12 | * The assembler implementation from Agner Fog, which this code is |
13 | * based on, can be found here: | |
14 | * http://www.agner.org/optimize/asmlib.zip | |
6a2d7a95 | 15 | * |
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16 | * This optimization for A/B is helpful if the divisor B is mostly |
17 | * runtime invariant. The reciprocal of B is calculated in the | |
18 | * slow-path with reciprocal_value(). The fast-path can then just use | |
19 | * a much faster multiplication operation with a variable dividend A | |
20 | * to calculate the division A/B. | |
6a2d7a95 ED |
21 | */ |
22 | ||
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23 | struct reciprocal_value { |
24 | u32 m; | |
25 | u8 sh1, sh2; | |
26 | }; | |
6a2d7a95 | 27 | |
809fa972 | 28 | struct reciprocal_value reciprocal_value(u32 d); |
6a2d7a95 | 29 | |
809fa972 | 30 | static inline u32 reciprocal_divide(u32 a, struct reciprocal_value R) |
6a2d7a95 | 31 | { |
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32 | u32 t = (u32)(((u64)a * R.m) >> 32); |
33 | return (t + ((a - t) >> R.sh1)) >> R.sh2; | |
6a2d7a95 | 34 | } |
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35 | |
36 | #endif /* _LINUX_RECIPROCAL_DIV_H */ |