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/*
* Copyright (C) 2023 Apple Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following disclaimer
* in the documentation and/or other materials provided with the
* distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
/*
* License header from dragonbox
* https://github.com/jk-jeon/dragonbox/blob/master/LICENSE-Boost
* https://github.com/jk-jeon/dragonbox/blob/master/LICENSE-Apache2-LLVM
*/
#pragma once
#include <wtf/dragonbox/detail/util.h>
namespace WTF {
namespace dragonbox {
namespace detail {
////////////////////////////////////////////////////////////////////////////////////////
// Utilities for fast/constexpr log computation.
////////////////////////////////////////////////////////////////////////////////////////
namespace log {
static_assert((-1 >> 1) == -1, "right-shift for signed integers must be arithmetic");
// Compute floor(e * c - s).
enum class multiply : uint32_t { };
enum class subtract : uint32_t { };
enum class shift : size_t { };
enum class min_exponent : int32_t { };
enum class max_exponent : int32_t { };
template<multiply m, subtract f, shift k, min_exponent e_min, max_exponent e_max>
constexpr int32_t compute(int32_t e) noexcept
{
ASSERT(static_cast<int32_t>(e_min) <= e && e <= static_cast<int32_t>(e_max));
return static_cast<int32_t>((static_cast<int32_t>(e) * static_cast<int32_t>(m) - static_cast<int32_t>(f)) >> size_t(k));
}
// For constexpr computation.
// Returns -1 when n = 0.
template<class UInt>
constexpr int32_t floor_log2(UInt n) noexcept
{
int32_t count = -1;
while (n) {
++count;
n >>= 1;
}
return count;
}
static constexpr int32_t floor_log10_pow2_min_exponent = -2620;
static constexpr int32_t floor_log10_pow2_max_exponent = 2620;
constexpr int32_t floor_log10_pow2(int32_t e) noexcept
{
return compute<multiply(315653), subtract(0), shift(20), min_exponent(floor_log10_pow2_min_exponent), max_exponent(floor_log10_pow2_max_exponent)>(e);
}
static constexpr int32_t floor_log2_pow10_min_exponent = -1233;
static constexpr int32_t floor_log2_pow10_max_exponent = 1233;
constexpr int32_t floor_log2_pow10(int32_t e) noexcept
{
return compute<multiply(1741647), subtract(0), shift(19), min_exponent(floor_log2_pow10_min_exponent), max_exponent(floor_log2_pow10_max_exponent)>(e);
}
static constexpr int32_t floor_log10_pow2_minus_log10_4_over_3_min_exponent = -2985;
static constexpr int32_t floor_log10_pow2_minus_log10_4_over_3_max_exponent = 2936;
constexpr int32_t floor_log10_pow2_minus_log10_4_over_3(int32_t e) noexcept
{
return compute<multiply(631305), subtract(261663), shift(21), min_exponent(floor_log10_pow2_minus_log10_4_over_3_min_exponent), max_exponent(floor_log10_pow2_minus_log10_4_over_3_max_exponent)>(e);
}
static constexpr int32_t floor_log5_pow2_min_exponent = -1831;
static constexpr int32_t floor_log5_pow2_max_exponent = 1831;
constexpr int32_t floor_log5_pow2(int32_t e) noexcept
{
return compute<multiply(225799), subtract(0), shift(19), min_exponent(floor_log5_pow2_min_exponent), max_exponent(floor_log5_pow2_max_exponent)>(e);
}
static constexpr int32_t floor_log5_pow2_minus_log5_3_min_exponent = -3543;
static constexpr int32_t floor_log5_pow2_minus_log5_3_max_exponent = 2427;
constexpr int32_t floor_log5_pow2_minus_log5_3(int32_t e) noexcept
{
return compute<multiply(451597), subtract(715764), shift(20), min_exponent(floor_log5_pow2_minus_log5_3_min_exponent), max_exponent(floor_log5_pow2_minus_log5_3_max_exponent)>(e);
}
} // namespace log
} // namespace detail
} // namespace dragonbox
} // namespace WTF
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