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