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1 #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  */
25 extern u32 reciprocal_value(u32 B);
26 
27 
reciprocal_divide(u32 A,u32 R)28 static inline u32 reciprocal_divide(u32 A, u32 R)
29 {
30 	return (u32)(((u64)A * R) >> 32);
31 }
32 #endif
33