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33 lines
846 B
33 lines
846 B
18 years ago
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#ifndef _LINUX_RECIPROCAL_DIV_H
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#define _LINUX_RECIPROCAL_DIV_H
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#include <linux/types.h>
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/*
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* This file describes reciprocical division.
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*
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* This optimizes the (A/B) problem, when A and B are two u32
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* and B is a known value (but not known at compile time)
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*
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* The math principle used is :
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* Let RECIPROCAL_VALUE(B) be (((1LL << 32) + (B - 1))/ B)
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* Then A / B = (u32)(((u64)(A) * (R)) >> 32)
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*
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* This replaces a divide by a multiply (and a shift), and
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* is generally less expensive in CPU cycles.
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*/
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/*
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* Computes the reciprocal value (R) for the value B of the divisor.
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* Should not be called before each reciprocal_divide(),
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* or else the performance is slower than a normal divide.
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*/
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extern u32 reciprocal_value(u32 B);
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static inline u32 reciprocal_divide(u32 A, u32 R)
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{
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return (u32)(((u64)A * R) >> 32);
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}
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#endif
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