linux-next/include/linux/reciprocal_div.h

#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