33 строки
846 B
C
33 строки
846 B
C
|
#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
|