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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                 :   12078441 :         return (u32)(((u64)A * R) >> 32);
      31                 :            : }
      32                 :            : #endif