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@@ -3,6 +3,11 @@
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*
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* Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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+ *
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+ * This program is free software; you can redistribute it and/or
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+ * modify it under the terms of the GNU General Public License
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+ * as published by the Free Software Foundation; either version
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+ * 2 of the License, or (at your option) any later version.
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*/
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#ifndef _LINUX_LOG2_H
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@@ -11,12 +16,6 @@
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#include <linux/types.h>
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#include <linux/bitops.h>
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-/*
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- * deal with unrepresentable constant logarithms
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- */
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-extern __attribute__((const, noreturn))
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-int ____ilog2_NaN(void);
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-
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/*
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* non-constant log of base 2 calculators
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* - the arch may override these in asm/bitops.h if they can be implemented
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@@ -39,19 +38,23 @@ int __ilog2_u64(u64 n)
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}
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#endif
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-/*
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- * Determine whether some value is a power of two, where zero is
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+/**
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+ * is_power_of_2() - check if a value is a power of two
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+ * @n: the value to check
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+ *
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+ * Determine whether some value is a power of two, where zero is
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* *not* considered a power of two.
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+ * Return: true if @n is a power of 2, otherwise false.
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*/
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-
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static inline __attribute__((const))
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bool is_power_of_2(unsigned long n)
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{
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return (n != 0 && ((n & (n - 1)) == 0));
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}
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-/*
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- * round up to nearest power of two
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+/**
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+ * __roundup_pow_of_two() - round up to nearest power of two
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+ * @n: value to round up
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*/
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static inline __attribute__((const))
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unsigned long __roundup_pow_of_two(unsigned long n)
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@@ -59,8 +62,9 @@ unsigned long __roundup_pow_of_two(unsigned long n)
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return 1UL << fls_long(n - 1);
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}
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-/*
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- * round down to nearest power of two
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+/**
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+ * __rounddown_pow_of_two() - round down to nearest power of two
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+ * @n: value to round down
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*/
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static inline __attribute__((const))
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unsigned long __rounddown_pow_of_two(unsigned long n)
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@@ -69,19 +73,19 @@ unsigned long __rounddown_pow_of_two(unsigned long n)
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}
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/**
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- * ilog2 - log of base 2 of 32-bit or a 64-bit unsigned value
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- * @n - parameter
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+ * ilog2 - log base 2 of 32-bit or a 64-bit unsigned value
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+ * @n: parameter
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*
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* constant-capable log of base 2 calculation
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* - this can be used to initialise global variables from constant data, hence
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- * the massive ternary operator construction
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+ * the massive ternary operator construction
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*
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* selects the appropriately-sized optimised version depending on sizeof(n)
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*/
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#define ilog2(n) \
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( \
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__builtin_constant_p(n) ? ( \
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- (n) < 1 ? ____ilog2_NaN() : \
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+ (n) < 2 ? 0 : \
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(n) & (1ULL << 63) ? 63 : \
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(n) & (1ULL << 62) ? 62 : \
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(n) & (1ULL << 61) ? 61 : \
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@@ -144,10 +148,7 @@ unsigned long __rounddown_pow_of_two(unsigned long n)
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(n) & (1ULL << 4) ? 4 : \
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(n) & (1ULL << 3) ? 3 : \
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(n) & (1ULL << 2) ? 2 : \
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- (n) & (1ULL << 1) ? 1 : \
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- (n) & (1ULL << 0) ? 0 : \
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- ____ilog2_NaN() \
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- ) : \
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+ 1) : \
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(sizeof(n) <= 4) ? \
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__ilog2_u32(n) : \
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__ilog2_u64(n) \
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@@ -155,7 +156,7 @@ unsigned long __rounddown_pow_of_two(unsigned long n)
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/**
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* roundup_pow_of_two - round the given value up to nearest power of two
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- * @n - parameter
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+ * @n: parameter
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*
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* round the given value up to the nearest power of two
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* - the result is undefined when n == 0
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@@ -172,7 +173,7 @@ unsigned long __rounddown_pow_of_two(unsigned long n)
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/**
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* rounddown_pow_of_two - round the given value down to nearest power of two
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- * @n - parameter
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+ * @n: parameter
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*
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* round the given value down to the nearest power of two
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* - the result is undefined when n == 0
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@@ -185,6 +186,12 @@ unsigned long __rounddown_pow_of_two(unsigned long n)
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__rounddown_pow_of_two(n) \
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)
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+static inline __attribute_const__
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+int __order_base_2(unsigned long n)
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+{
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+ return n > 1 ? ilog2(n - 1) + 1 : 0;
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+}
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+
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/**
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* order_base_2 - calculate the (rounded up) base 2 order of the argument
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* @n: parameter
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@@ -198,7 +205,11 @@ unsigned long __rounddown_pow_of_two(unsigned long n)
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* ob2(5) = 3
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* ... and so on.
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*/
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-
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-#define order_base_2(n) ilog2(roundup_pow_of_two(n))
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-
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+#define order_base_2(n) \
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+( \
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+ __builtin_constant_p(n) ? ( \
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+ ((n) == 0 || (n) == 1) ? 0 : \
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+ ilog2((n) - 1) + 1) : \
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+ __order_base_2(n) \
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+)
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#endif /* _LINUX_LOG2_H */
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