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Eric Dumazet6a2d7a92006-12-13 00:34:27 -08001#ifndef _LINUX_RECIPROCAL_DIV_H
2#define _LINUX_RECIPROCAL_DIV_H
3
4#include <linux/types.h>
5
6/*
7 * This file describes reciprocical division.
8 *
9 * This optimizes the (A/B) problem, when A and B are two u32
10 * and B is a known value (but not known at compile time)
11 *
12 * The math principle used is :
13 * Let RECIPROCAL_VALUE(B) be (((1LL << 32) + (B - 1))/ B)
14 * Then A / B = (u32)(((u64)(A) * (R)) >> 32)
15 *
16 * This replaces a divide by a multiply (and a shift), and
17 * is generally less expensive in CPU cycles.
18 */
19
20/*
21 * Computes the reciprocal value (R) for the value B of the divisor.
22 * Should not be called before each reciprocal_divide(),
23 * or else the performance is slower than a normal divide.
24 */
25extern u32 reciprocal_value(u32 B);
26
27
28static inline u32 reciprocal_divide(u32 A, u32 R)
29{
30 return (u32)(((u64)A * R) >> 32);
31}
32#endif