mirror of
https://github.com/mozilla/gecko-dev.git
synced 2024-12-05 12:05:22 +00:00
2a0942be41
--HG-- extra : rebase_source : 668cd394806203ddfa34bd4f226335ff26c846b5
502 lines
13 KiB
C++
502 lines
13 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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/* mfbt maths algorithms. */
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#ifndef mozilla_MathAlgorithms_h
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#define mozilla_MathAlgorithms_h
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#include "mozilla/Assertions.h"
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#include "mozilla/TypeTraits.h"
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#include <cmath>
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#include <limits.h>
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#include <stdint.h>
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namespace mozilla {
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// Greatest Common Divisor
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template<typename IntegerType>
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MOZ_ALWAYS_INLINE IntegerType
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EuclidGCD(IntegerType aA, IntegerType aB)
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{
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// Euclid's algorithm; O(N) in the worst case. (There are better
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// ways, but we don't need them for the current use of this algo.)
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MOZ_ASSERT(aA > IntegerType(0));
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MOZ_ASSERT(aB > IntegerType(0));
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while (aA != aB) {
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if (aA > aB) {
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aA = aA - aB;
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} else {
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aB = aB - aA;
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}
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}
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return aA;
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}
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// Least Common Multiple
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template<typename IntegerType>
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MOZ_ALWAYS_INLINE IntegerType
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EuclidLCM(IntegerType aA, IntegerType aB)
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{
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// Divide first to reduce overflow risk.
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return (aA / EuclidGCD(aA, aB)) * aB;
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}
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namespace detail {
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template<typename T>
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struct AllowDeprecatedAbsFixed : FalseType {};
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template<> struct AllowDeprecatedAbsFixed<int32_t> : TrueType {};
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template<> struct AllowDeprecatedAbsFixed<int64_t> : TrueType {};
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template<typename T>
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struct AllowDeprecatedAbs : AllowDeprecatedAbsFixed<T> {};
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template<> struct AllowDeprecatedAbs<int> : TrueType {};
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template<> struct AllowDeprecatedAbs<long> : TrueType {};
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} // namespace detail
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// DO NOT USE DeprecatedAbs. It exists only until its callers can be converted
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// to Abs below, and it will be removed when all callers have been changed.
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template<typename T>
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inline typename mozilla::EnableIf<detail::AllowDeprecatedAbs<T>::value, T>::Type
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DeprecatedAbs(const T aValue)
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{
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// The absolute value of the smallest possible value of a signed-integer type
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// won't fit in that type (on twos-complement systems -- and we're blithely
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// assuming we're on such systems, for the non-<stdint.h> types listed above),
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// so assert that the input isn't that value.
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//
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// This is the case if: the value is non-negative; or if adding one (giving a
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// value in the range [-maxvalue, 0]), then negating (giving a value in the
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// range [0, maxvalue]), doesn't produce maxvalue (because in twos-complement,
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// (minvalue + 1) == -maxvalue).
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MOZ_ASSERT(aValue >= 0 ||
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-(aValue + 1) != T((1ULL << (CHAR_BIT * sizeof(T) - 1)) - 1),
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"You can't negate the smallest possible negative integer!");
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return aValue >= 0 ? aValue : -aValue;
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}
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namespace detail {
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// For now mozilla::Abs only takes intN_T, the signed natural types, and
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// float/double/long double. Feel free to add overloads for other standard,
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// signed types if you need them.
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template<typename T>
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struct AbsReturnTypeFixed;
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template<> struct AbsReturnTypeFixed<int8_t> { typedef uint8_t Type; };
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template<> struct AbsReturnTypeFixed<int16_t> { typedef uint16_t Type; };
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template<> struct AbsReturnTypeFixed<int32_t> { typedef uint32_t Type; };
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template<> struct AbsReturnTypeFixed<int64_t> { typedef uint64_t Type; };
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template<typename T>
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struct AbsReturnType : AbsReturnTypeFixed<T> {};
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template<> struct AbsReturnType<char> :
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EnableIf<char(-1) < char(0), unsigned char> {};
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template<> struct AbsReturnType<signed char> { typedef unsigned char Type; };
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template<> struct AbsReturnType<short> { typedef unsigned short Type; };
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template<> struct AbsReturnType<int> { typedef unsigned int Type; };
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template<> struct AbsReturnType<long> { typedef unsigned long Type; };
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template<> struct AbsReturnType<long long> { typedef unsigned long long Type; };
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template<> struct AbsReturnType<float> { typedef float Type; };
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template<> struct AbsReturnType<double> { typedef double Type; };
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template<> struct AbsReturnType<long double> { typedef long double Type; };
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} // namespace detail
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template<typename T>
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inline typename detail::AbsReturnType<T>::Type
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Abs(const T aValue)
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{
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typedef typename detail::AbsReturnType<T>::Type ReturnType;
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return aValue >= 0 ? ReturnType(aValue) : ~ReturnType(aValue) + 1;
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}
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template<>
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inline float
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Abs<float>(const float aFloat)
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{
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return std::fabs(aFloat);
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}
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template<>
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inline double
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Abs<double>(const double aDouble)
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{
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return std::fabs(aDouble);
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}
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template<>
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inline long double
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Abs<long double>(const long double aLongDouble)
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{
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return std::fabs(aLongDouble);
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}
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} // namespace mozilla
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#if defined(_WIN32) && (_MSC_VER >= 1300) && \
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(defined(_M_IX86) || defined(_M_AMD64) || defined(_M_X64))
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# define MOZ_BITSCAN_WINDOWS
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# include <intrin.h>
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# pragma intrinsic(_BitScanForward, _BitScanReverse)
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# if defined(_M_AMD64) || defined(_M_X64)
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# define MOZ_BITSCAN_WINDOWS64
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# pragma intrinsic(_BitScanForward64, _BitScanReverse64)
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# endif
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#endif
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namespace mozilla {
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namespace detail {
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#if defined(MOZ_BITSCAN_WINDOWS)
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inline uint_fast8_t
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CountLeadingZeroes32(uint32_t aValue)
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{
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unsigned long index;
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_BitScanReverse(&index, static_cast<unsigned long>(aValue));
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return uint_fast8_t(31 - index);
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}
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inline uint_fast8_t
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CountTrailingZeroes32(uint32_t aValue)
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{
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unsigned long index;
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_BitScanForward(&index, static_cast<unsigned long>(aValue));
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return uint_fast8_t(index);
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}
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inline uint_fast8_t
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CountPopulation32(uint32_t aValue)
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{
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uint32_t x = aValue - ((aValue >> 1) & 0x55555555);
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x = (x & 0x33333333) + ((x >> 2) & 0x33333333);
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return (((x + (x >> 4)) & 0xf0f0f0f) * 0x1010101) >> 24;
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}
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inline uint_fast8_t
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CountPopulation64(uint64_t aValue)
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{
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return uint_fast8_t(CountPopulation32(aValue & 0xffffffff) +
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CountPopulation32(aValue >> 32));
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}
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inline uint_fast8_t
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CountLeadingZeroes64(uint64_t aValue)
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{
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#if defined(MOZ_BITSCAN_WINDOWS64)
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unsigned long index;
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_BitScanReverse64(&index, static_cast<unsigned __int64>(aValue));
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return uint_fast8_t(63 - index);
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#else
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uint32_t hi = uint32_t(aValue >> 32);
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if (hi != 0) {
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return CountLeadingZeroes32(hi);
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}
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return 32u + CountLeadingZeroes32(uint32_t(aValue));
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#endif
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}
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inline uint_fast8_t
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CountTrailingZeroes64(uint64_t aValue)
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{
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#if defined(MOZ_BITSCAN_WINDOWS64)
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unsigned long index;
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_BitScanForward64(&index, static_cast<unsigned __int64>(aValue));
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return uint_fast8_t(index);
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#else
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uint32_t lo = uint32_t(aValue);
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if (lo != 0) {
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return CountTrailingZeroes32(lo);
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}
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return 32u + CountTrailingZeroes32(uint32_t(aValue >> 32));
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#endif
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}
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# ifdef MOZ_HAVE_BITSCAN64
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# undef MOZ_HAVE_BITSCAN64
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# endif
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#elif defined(__clang__) || defined(__GNUC__)
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# if defined(__clang__)
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# if !__has_builtin(__builtin_ctz) || !__has_builtin(__builtin_clz)
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# error "A clang providing __builtin_c[lt]z is required to build"
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# endif
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# else
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// gcc has had __builtin_clz and friends since 3.4: no need to check.
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# endif
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inline uint_fast8_t
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CountLeadingZeroes32(uint32_t aValue)
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{
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return __builtin_clz(aValue);
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}
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inline uint_fast8_t
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CountTrailingZeroes32(uint32_t aValue)
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{
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return __builtin_ctz(aValue);
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}
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inline uint_fast8_t
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CountPopulation32(uint32_t aValue)
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{
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return __builtin_popcount(aValue);
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}
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inline uint_fast8_t
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CountPopulation64(uint64_t aValue)
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{
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return __builtin_popcountll(aValue);
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}
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inline uint_fast8_t
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CountLeadingZeroes64(uint64_t aValue)
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{
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return __builtin_clzll(aValue);
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}
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inline uint_fast8_t
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CountTrailingZeroes64(uint64_t aValue)
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{
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return __builtin_ctzll(aValue);
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}
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#else
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# error "Implement these!"
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inline uint_fast8_t CountLeadingZeroes32(uint32_t aValue) MOZ_DELETE;
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inline uint_fast8_t CountTrailingZeroes32(uint32_t aValue) MOZ_DELETE;
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inline uint_fast8_t CountPopulation32(uint32_t aValue) MOZ_DELETE;
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inline uint_fast8_t CountPopulation64(uint64_t aValue) MOZ_DELETE;
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inline uint_fast8_t CountLeadingZeroes64(uint64_t aValue) MOZ_DELETE;
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inline uint_fast8_t CountTrailingZeroes64(uint64_t aValue) MOZ_DELETE;
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#endif
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} // namespace detail
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/**
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* Compute the number of high-order zero bits in the NON-ZERO number |aValue|.
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* That is, looking at the bitwise representation of the number, with the
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* highest- valued bits at the start, return the number of zeroes before the
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* first one is observed.
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*
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* CountLeadingZeroes32(0xF0FF1000) is 0;
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* CountLeadingZeroes32(0x7F8F0001) is 1;
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* CountLeadingZeroes32(0x3FFF0100) is 2;
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* CountLeadingZeroes32(0x1FF50010) is 3; and so on.
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*/
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inline uint_fast8_t
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CountLeadingZeroes32(uint32_t aValue)
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{
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MOZ_ASSERT(aValue != 0);
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return detail::CountLeadingZeroes32(aValue);
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}
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/**
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* Compute the number of low-order zero bits in the NON-ZERO number |aValue|.
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* That is, looking at the bitwise representation of the number, with the
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* lowest- valued bits at the start, return the number of zeroes before the
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* first one is observed.
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*
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* CountTrailingZeroes32(0x0100FFFF) is 0;
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* CountTrailingZeroes32(0x7000FFFE) is 1;
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* CountTrailingZeroes32(0x0080FFFC) is 2;
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* CountTrailingZeroes32(0x0080FFF8) is 3; and so on.
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*/
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inline uint_fast8_t
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CountTrailingZeroes32(uint32_t aValue)
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{
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MOZ_ASSERT(aValue != 0);
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return detail::CountTrailingZeroes32(aValue);
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}
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/**
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* Compute the number of one bits in the number |aValue|,
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*/
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inline uint_fast8_t
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CountPopulation32(uint32_t aValue)
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{
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return detail::CountPopulation32(aValue);
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}
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/** Analogous to CoutPopulation32, but for 64-bit numbers */
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inline uint_fast8_t
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CountPopulation64(uint64_t aValue)
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{
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return detail::CountPopulation64(aValue);
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}
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/** Analogous to CountLeadingZeroes32, but for 64-bit numbers. */
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inline uint_fast8_t
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CountLeadingZeroes64(uint64_t aValue)
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{
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MOZ_ASSERT(aValue != 0);
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return detail::CountLeadingZeroes64(aValue);
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}
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/** Analogous to CountTrailingZeroes32, but for 64-bit numbers. */
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inline uint_fast8_t
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CountTrailingZeroes64(uint64_t aValue)
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{
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MOZ_ASSERT(aValue != 0);
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return detail::CountTrailingZeroes64(aValue);
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}
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namespace detail {
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template<typename T, size_t Size = sizeof(T)>
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class CeilingLog2;
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template<typename T>
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class CeilingLog2<T, 4>
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{
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public:
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static uint_fast8_t compute(const T aValue)
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{
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// Check for <= 1 to avoid the == 0 undefined case.
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return aValue <= 1 ? 0u : 32u - CountLeadingZeroes32(aValue - 1);
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}
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};
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template<typename T>
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class CeilingLog2<T, 8>
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{
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public:
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static uint_fast8_t compute(const T aValue)
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{
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// Check for <= 1 to avoid the == 0 undefined case.
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return aValue <= 1 ? 0 : 64 - CountLeadingZeroes64(aValue - 1);
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}
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};
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} // namespace detail
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/**
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* Compute the log of the least power of 2 greater than or equal to |aValue|.
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*
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* CeilingLog2(0..1) is 0;
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* CeilingLog2(2) is 1;
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* CeilingLog2(3..4) is 2;
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* CeilingLog2(5..8) is 3;
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* CeilingLog2(9..16) is 4; and so on.
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*/
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template<typename T>
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inline uint_fast8_t
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CeilingLog2(const T aValue)
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{
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return detail::CeilingLog2<T>::compute(aValue);
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}
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/** A CeilingLog2 variant that accepts only size_t. */
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inline uint_fast8_t
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CeilingLog2Size(size_t aValue)
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{
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return CeilingLog2(aValue);
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}
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namespace detail {
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template<typename T, size_t Size = sizeof(T)>
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class FloorLog2;
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template<typename T>
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class FloorLog2<T, 4>
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{
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public:
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static uint_fast8_t compute(const T aValue)
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{
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return 31u - CountLeadingZeroes32(aValue | 1);
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}
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};
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template<typename T>
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class FloorLog2<T, 8>
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{
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public:
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static uint_fast8_t compute(const T aValue)
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{
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return 63u - CountLeadingZeroes64(aValue | 1);
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}
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};
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} // namespace detail
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/**
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* Compute the log of the greatest power of 2 less than or equal to |aValue|.
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*
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* FloorLog2(0..1) is 0;
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* FloorLog2(2..3) is 1;
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* FloorLog2(4..7) is 2;
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* FloorLog2(8..15) is 3; and so on.
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*/
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template<typename T>
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inline uint_fast8_t
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FloorLog2(const T aValue)
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{
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return detail::FloorLog2<T>::compute(aValue);
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}
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/** A FloorLog2 variant that accepts only size_t. */
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inline uint_fast8_t
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FloorLog2Size(size_t aValue)
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{
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return FloorLog2(aValue);
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}
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/*
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* Compute the smallest power of 2 greater than or equal to |x|. |x| must not
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* be so great that the computed value would overflow |size_t|.
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*/
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inline size_t
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RoundUpPow2(size_t aValue)
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{
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MOZ_ASSERT(aValue <= (size_t(1) << (sizeof(size_t) * CHAR_BIT - 1)),
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"can't round up -- will overflow!");
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return size_t(1) << CeilingLog2(aValue);
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}
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/**
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* Rotates the bits of the given value left by the amount of the shift width.
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*/
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template<typename T>
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inline T
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RotateLeft(const T aValue, uint_fast8_t aShift)
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{
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MOZ_ASSERT(aShift < sizeof(T) * CHAR_BIT, "Shift value is too large!");
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static_assert(IsUnsigned<T>::value, "Rotates require unsigned values");
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return (aValue << aShift) | (aValue >> (sizeof(T) * CHAR_BIT - aShift));
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}
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/**
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* Rotates the bits of the given value right by the amount of the shift width.
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*/
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template<typename T>
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inline T
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RotateRight(const T aValue, uint_fast8_t aShift)
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{
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MOZ_ASSERT(aShift < sizeof(T) * CHAR_BIT, "Shift value is too large!");
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static_assert(IsUnsigned<T>::value, "Rotates require unsigned values");
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return (aValue >> aShift) | (aValue << (sizeof(T) * CHAR_BIT - aShift));
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}
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} /* namespace mozilla */
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#endif /* mozilla_MathAlgorithms_h */
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