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35 lines
993 B
35 lines
993 B
#ifndef _LINUX_RECIPROCAL_DIV_H |
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#define _LINUX_RECIPROCAL_DIV_H |
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#include <linux/types.h> |
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/* |
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* This algorithm is based on the paper "Division by Invariant |
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* Integers Using Multiplication" by Torbjörn Granlund and Peter |
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* L. Montgomery. |
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* |
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* The assembler implementation from Agner Fog, which this code is |
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* based on, can be found here: |
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* http://www.agner.org/optimize/asmlib.zip |
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* |
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* This optimization for A/B is helpful if the divisor B is mostly |
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* runtime invariant. The reciprocal of B is calculated in the |
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* slow-path with reciprocal_value(). The fast-path can then just use |
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* a much faster multiplication operation with a variable dividend A |
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* to calculate the division A/B. |
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*/ |
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struct reciprocal_value { |
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u32 m; |
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u8 sh1, sh2; |
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}; |
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struct reciprocal_value reciprocal_value(u32 d); |
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static inline u32 reciprocal_divide(u32 a, struct reciprocal_value R) |
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{ |
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u32 t = (u32)(((u64)a * R.m) >> 32); |
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return (t + ((a - t) >> R.sh1)) >> R.sh2; |
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} |
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#endif /* _LINUX_RECIPROCAL_DIV_H */
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