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