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TOMOYO Linux Cross Reference
Linux/include/linux/reciprocal_div.h

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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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