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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 | |
28 | static inline u32 reciprocal_divide(u32 A, u32 R) |
29 | { |
30 | return (u32)(((u64)A * R) >> 32); |
31 | } |
32 | #endif |
33 |
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