This commit was manufactured by cvs2svn to create branch 'vserver'.

[linux-2.6.git] / include / linux / reciprocal_div.h

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