mirror of https://github.com/F-Stack/f-stack.git
42 lines
1.1 KiB
C
42 lines
1.1 KiB
C
/*
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* Reciprocal divide
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*
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* Used with permission from original authors
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* Hannes Frederic Sowa and Daniel Borkmann
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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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#ifndef _RTE_RECIPROCAL_H_
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#define _RTE_RECIPROCAL_H_
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#include <stdint.h>
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struct rte_reciprocal {
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uint32_t m;
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uint8_t sh1, sh2;
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};
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static inline uint32_t rte_reciprocal_divide(uint32_t a, struct rte_reciprocal R)
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{
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uint32_t t = (uint32_t)(((uint64_t)a * R.m) >> 32);
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return (t + ((a - t) >> R.sh1)) >> R.sh2;
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}
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struct rte_reciprocal rte_reciprocal_value(uint32_t d);
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#endif /* _RTE_RECIPROCAL_H_ */
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