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/*
* Reciprocal divide
*
* Used with permission from original authors
* Hannes Frederic Sowa and Daniel Borkmann
*
* This algorithm is based on the paper "Division by Invariant
* Integers Using Multiplication" by Torbjörn Granlund and Peter
* L. Montgomery.
*
* The assembler implementation from Agner Fog, which this code is
* based on, can be found here:
* http://www.agner.org/optimize/asmlib.zip
*
* This optimization for A/B is helpful if the divisor B is mostly
* runtime invariant. The reciprocal of B is calculated in the
* slow-path with reciprocal_value(). The fast-path can then just use
* a much faster multiplication operation with a variable dividend A
* to calculate the division A/B.
*/
#ifndef _RTE_RECIPROCAL_H_
#define _RTE_RECIPROCAL_H_
struct rte_reciprocal {
uint32_t m;
uint8_t sh1, sh2;
};
static inline uint32_t rte_reciprocal_divide(uint32_t a, struct rte_reciprocal R)
{
uint32_t t = (uint32_t)(((uint64_t)a * R.m) >> 32);
return (t + ((a - t) >> R.sh1)) >> R.sh2;
}
struct rte_reciprocal rte_reciprocal_value(uint32_t d);
#endif /* _RTE_RECIPROCAL_H_ */
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