Viewing file:  reciprocal_div.h (1.01 KB) -rw-r--r--
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/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_RECIPROCAL_DIV_H
#define _LINUX_RECIPROCAL_DIV_H
#include <linux/types.h>
/*
* 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.
*/
struct reciprocal_value {
u32 m;
u8 sh1, sh2;
};
struct reciprocal_value reciprocal_value(u32 d);
static inline u32 reciprocal_divide(u32 a, struct reciprocal_value R)
{
u32 t = (u32)(((u64)a * R.m) >> 32);
return (t + ((a - t) >> R.sh1)) >> R.sh2;
}
#endif /* _LINUX_RECIPROCAL_DIV_H */
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