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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/log.h>
#include <wtf/dragonbox/detail/util.h>
#include <wtf/dragonbox/detail/wuint.h>
namespace WTF {
namespace dragonbox {
namespace detail {
////////////////////////////////////////////////////////////////////////////////////////
// Utilities for fast divisibility tests.
////////////////////////////////////////////////////////////////////////////////////////
namespace div {
// Replace n by floor(n / 10^N).
// Returns true if and only if n is divisible by 10^N.
// Precondition: n <= 10^(N+1)
// !!It takes an in-out parameter!!
template<int32_t N>
struct divide_by_pow10_info;
template<>
struct divide_by_pow10_info<1> {
static constexpr uint32_t magic_number = 6554;
static constexpr int32_t shift_amount = 16;
};
template<>
struct divide_by_pow10_info<2> {
static constexpr uint32_t magic_number = 656;
static constexpr int32_t shift_amount = 16;
};
template<int32_t N>
constexpr bool check_divisibility_and_divide_by_pow10(uint32_t& n) noexcept
{
// Make sure the computation for max_n does not overflow.
static_assert(N + 1 <= log::floor_log10_pow2(31), "");
ASSERT(n <= compute_power<N + 1>(static_cast<uint32_t>(10)));
using info = divide_by_pow10_info<N>;
n *= info::magic_number;
constexpr auto mask = static_cast<uint32_t>(static_cast<uint32_t>(1) << info::shift_amount) - 1;
bool result = ((n & mask) < info::magic_number);
n >>= info::shift_amount;
return result;
}
// Compute floor(n / 10^N) for small n and N.
// Precondition: n <= 10^(N+1)
template<int32_t N>
constexpr uint32_t small_division_by_pow10(uint32_t n) noexcept
{
// Make sure the computation for max_n does not overflow.
static_assert(N + 1 <= log::floor_log10_pow2(31), "");
ASSERT(n <= compute_power<N + 1>(static_cast<uint32_t>(10)));
return (n * divide_by_pow10_info<N>::magic_number) >> divide_by_pow10_info<N>::shift_amount;
}
// Compute floor(n / 10^N) for small N.
// Precondition: n <= n_max
template<int32_t N, class UInt, UInt n_max>
constexpr UInt divide_by_pow10(UInt n) noexcept
{
static_assert(N >= 0, "");
// Specialize for 32-bit division by 100.
// Compiler is supposed to generate the identical code for just writing
// "n / 100", but for some reason MSVC generates an inefficient code
// (mul + mov for no apparent reason, instead of single imul),
// so we does this manually.
if constexpr (std::is_same<UInt, uint32_t>::value && N == 2) {
return static_cast<uint32_t>(wuint::umul64(n, static_cast<uint32_t>(1374389535)) >> 37);
} else if constexpr (std::is_same<UInt, uint64_t>::value && N == 3 && n_max <= static_cast<uint64_t>(15534100272597517998ull)) {
// Specialize for 64-bit division by 1000.
// Ensure that the correctness condition is met.
return wuint::umul128_upper64(n, static_cast<uint64_t>(2361183241434822607ull)) >> 7;
} else {
constexpr auto divisor = compute_power<N>(UInt(10));
return n / divisor;
}
}
} // namespace div
} // namespace detail
} // namespace dragonbox
} // namespace WTF
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