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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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