275 lines
8.1 KiB
C++
275 lines
8.1 KiB
C++
// Copyright 2023 Matt Borland
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// Distributed under the Boost Software License, Version 1.0.
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// https://www.boost.org/LICENSE_1_0.txt
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#ifndef BOOST_CHARCONV_DETAIL_INTEGER_SEARCH_TREES_HPP
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#define BOOST_CHARCONV_DETAIL_INTEGER_SEARCH_TREES_HPP
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// https://stackoverflow.com/questions/1489830/efficient-way-to-determine-number-of-digits-in-an-integer?page=1&tab=scoredesc#tab-top
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// https://graphics.stanford.edu/~seander/bithacks.html
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#include <boost/charconv/detail/config.hpp>
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#include <boost/charconv/detail/emulated128.hpp>
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#include <limits>
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#include <array>
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#include <cstdint>
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namespace boost { namespace charconv { namespace detail {
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// Generic solution
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template <typename T>
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BOOST_CHARCONV_CXX14_CONSTEXPR int num_digits(T x) noexcept
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{
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int digits = 0;
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while (x)
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{
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x /= 10;
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++digits;
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}
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return digits;
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}
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template <>
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BOOST_CHARCONV_CXX14_CONSTEXPR int num_digits(std::uint32_t x) noexcept
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{
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if (x >= UINT32_C(10000))
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{
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if (x >= UINT32_C(10000000))
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{
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if (x >= UINT32_C(100000000))
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{
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if (x >= UINT32_C(1000000000))
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{
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return 10;
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}
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return 9;
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}
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return 8;
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}
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else if (x >= UINT32_C(100000))
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{
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if (x >= UINT32_C(1000000))
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{
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return 7;
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}
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return 6;
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}
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return 5;
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}
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else if (x >= UINT32_C(100))
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{
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if (x >= UINT32_C(1000))
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{
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return 4;
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}
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return 3;
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}
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else if (x >= UINT32_C(10))
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{
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return 2;
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}
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return 1;
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}
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template <>
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BOOST_CHARCONV_CXX14_CONSTEXPR int num_digits(std::uint64_t x) noexcept
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{
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if (x >= UINT64_C(10000000000))
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{
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if (x >= UINT64_C(100000000000000))
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{
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if (x >= UINT64_C(10000000000000000))
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{
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if (x >= UINT64_C(100000000000000000))
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{
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if (x >= UINT64_C(1000000000000000000))
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{
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if (x >= UINT64_C(10000000000000000000))
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{
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return 20;
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}
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return 19;
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}
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return 18;
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}
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return 17;
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}
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else if (x >= UINT64_C(1000000000000000))
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{
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return 16;
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}
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return 15;
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}
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if (x >= UINT64_C(1000000000000))
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{
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if (x >= UINT64_C(10000000000000))
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{
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return 14;
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}
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return 13;
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}
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if (x >= UINT64_C(100000000000))
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{
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return 12;
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}
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return 11;
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}
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else if (x >= UINT64_C(100000))
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{
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if (x >= UINT64_C(10000000))
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{
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if (x >= UINT64_C(100000000))
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{
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if (x >= UINT64_C(1000000000))
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{
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return 10;
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}
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return 9;
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}
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return 8;
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}
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if (x >= UINT64_C(1000000))
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{
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return 7;
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}
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return 6;
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}
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if (x >= UINT64_C(100))
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{
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if (x >= UINT64_C(1000))
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{
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if (x >= UINT64_C(10000))
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{
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return 5;
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}
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return 4;
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}
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return 3;
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}
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if (x >= UINT64_C(10))
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{
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return 2;
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}
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return 1;
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}
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#ifdef BOOST_MSVC
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# pragma warning(push)
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# pragma warning(disable: 4307) // MSVC 14.1 warns of intergral constant overflow
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#endif
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BOOST_CHARCONV_CXX14_CONSTEXPR int num_digits(uint128 x) noexcept
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{
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if (x.high == 0)
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{
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return num_digits(x.low);
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}
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BOOST_CHARCONV_CXX14_CONSTEXPR_NO_INLINE uint128 digits_39 = static_cast<uint128>(UINT64_C(10000000000000000000)) *
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static_cast<uint128>(UINT64_C(10000000000000000000));
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uint128 current_power_of_10 = digits_39;
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for (int i = 39; i > 0; --i)
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{
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if (x >= current_power_of_10)
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{
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return i;
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}
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current_power_of_10 /= 10U;
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}
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return 1;
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}
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#ifdef BOOST_MSVC
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# pragma warning(pop)
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#endif
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#ifdef BOOST_CHARCONV_HAS_INT128
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static constexpr std::array<std::uint64_t, 20> powers_of_10 =
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{{
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UINT64_C(1), UINT64_C(10), UINT64_C(100), UINT64_C(1000), UINT64_C(10000), UINT64_C(100000), UINT64_C(1000000),
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UINT64_C(10000000), UINT64_C(100000000), UINT64_C(1000000000), UINT64_C(10000000000), UINT64_C(100000000000),
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UINT64_C(1000000000000), UINT64_C(10000000000000), UINT64_C(100000000000000), UINT64_C(1000000000000000),
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UINT64_C(10000000000000000), UINT64_C(100000000000000000), UINT64_C(1000000000000000000), UINT64_C(10000000000000000000)
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}};
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// Assume that if someone is using 128 bit ints they are favoring the top end of the range
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// Max value is 340,282,366,920,938,463,463,374,607,431,768,211,455 (39 digits)
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BOOST_CHARCONV_CXX14_CONSTEXPR int num_digits(boost::uint128_type x) noexcept
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{
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// There is no literal for boost::uint128_type, so we need to calculate them using the max value of the
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// std::uint64_t powers of 10
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constexpr boost::uint128_type digits_39 = static_cast<boost::uint128_type>(UINT64_C(10000000000000000000)) *
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static_cast<boost::uint128_type>(UINT64_C(10000000000000000000));
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constexpr boost::uint128_type digits_38 = digits_39 / 10;
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constexpr boost::uint128_type digits_37 = digits_38 / 10;
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constexpr boost::uint128_type digits_36 = digits_37 / 10;
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constexpr boost::uint128_type digits_35 = digits_36 / 10;
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constexpr boost::uint128_type digits_34 = digits_35 / 10;
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constexpr boost::uint128_type digits_33 = digits_34 / 10;
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constexpr boost::uint128_type digits_32 = digits_33 / 10;
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constexpr boost::uint128_type digits_31 = digits_32 / 10;
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constexpr boost::uint128_type digits_30 = digits_31 / 10;
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constexpr boost::uint128_type digits_29 = digits_30 / 10;
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constexpr boost::uint128_type digits_28 = digits_29 / 10;
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constexpr boost::uint128_type digits_27 = digits_28 / 10;
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constexpr boost::uint128_type digits_26 = digits_27 / 10;
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constexpr boost::uint128_type digits_25 = digits_26 / 10;
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constexpr boost::uint128_type digits_24 = digits_25 / 10;
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constexpr boost::uint128_type digits_23 = digits_24 / 10;
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constexpr boost::uint128_type digits_22 = digits_23 / 10;
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constexpr boost::uint128_type digits_21 = digits_22 / 10;
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return (x >= digits_39) ? 39 :
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(x >= digits_38) ? 38 :
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(x >= digits_37) ? 37 :
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(x >= digits_36) ? 36 :
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(x >= digits_35) ? 35 :
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(x >= digits_34) ? 34 :
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(x >= digits_33) ? 33 :
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(x >= digits_32) ? 32 :
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(x >= digits_31) ? 31 :
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(x >= digits_30) ? 30 :
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(x >= digits_29) ? 29 :
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(x >= digits_28) ? 28 :
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(x >= digits_27) ? 27 :
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(x >= digits_26) ? 26 :
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(x >= digits_25) ? 25 :
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(x >= digits_24) ? 24 :
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(x >= digits_23) ? 23 :
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(x >= digits_22) ? 22 :
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(x >= digits_21) ? 21 :
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(x >= powers_of_10[19]) ? 20 :
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(x >= powers_of_10[18]) ? 19 :
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(x >= powers_of_10[17]) ? 18 :
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(x >= powers_of_10[16]) ? 17 :
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(x >= powers_of_10[15]) ? 16 :
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(x >= powers_of_10[14]) ? 15 :
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(x >= powers_of_10[13]) ? 14 :
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(x >= powers_of_10[12]) ? 13 :
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(x >= powers_of_10[11]) ? 12 :
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(x >= powers_of_10[10]) ? 11 :
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(x >= powers_of_10[9]) ? 10 :
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(x >= powers_of_10[8]) ? 9 :
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(x >= powers_of_10[7]) ? 8 :
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(x >= powers_of_10[6]) ? 7 :
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(x >= powers_of_10[5]) ? 6 :
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(x >= powers_of_10[4]) ? 5 :
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(x >= powers_of_10[3]) ? 4 :
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(x >= powers_of_10[2]) ? 3 :
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(x >= powers_of_10[1]) ? 2 :
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(x >= powers_of_10[0]) ? 1 : 0;
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}
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#endif
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}}} // Namespace boost::charconv::detail
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#endif // BOOST_CHARCONV_DETAIL_INTEGER_SEARCH_TREES_HPP
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