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Add binary search trees for 32, 64 and 128 bit types

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Matt Borland
2023-01-18 11:36:04 -08:00
parent 807c3ea028
commit dea69677eb
2 changed files with 234 additions and 0 deletions
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233
include/boost/charconv/detail/integer_search_trees.hpp Normal file
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// 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 "../config.hpp"
#include <limits>
#include <array>
#include <cstdint>
// Generic solution
template <typename T>
BOOST_CXX14_CONSTEXPR int num_digits(T x) noexcept
{
int digits = 0;
while (x)
{
x /= 10;
++digits;
}
return digits;
}
template <>
BOOST_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_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 __GLIBCXX_TYPE_INT_N_0
static constexpr std::array<std::uint64_t, 20> powers_of_10 =
{{
1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000, 10000000000,
100000000000, 1000000000000, 10000000000000, 100000000000000, 1000000000000000, 10000000000000000,
100000000000000000, 1000000000000000000, 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_CXX14_CONSTEXPR int num_digits(unsigned __int128 x) noexcept
{
// There is not literal for unsigned __int128 so we need to calculate them using the max value of the
// std::uint64_t powers of 10
constexpr unsigned __int128 digits_39 = static_cast<unsigned __int128>(powers_of_10[19]) * static_cast<unsigned __int128>(powers_of_10[18]);
constexpr unsigned __int128 digits_38 = digits_39 / 10;
constexpr unsigned __int128 digits_37 = digits_38 / 10;
constexpr unsigned __int128 digits_36 = digits_37 / 10;
constexpr unsigned __int128 digits_35 = digits_36 / 10;
constexpr unsigned __int128 digits_34 = digits_35 / 10;
constexpr unsigned __int128 digits_33 = digits_34 / 10;
constexpr unsigned __int128 digits_32 = digits_33 / 10;
constexpr unsigned __int128 digits_31 = digits_32 / 10;
constexpr unsigned __int128 digits_30 = digits_31 / 10;
constexpr unsigned __int128 digits_29 = digits_30 / 10;
constexpr unsigned __int128 digits_28 = digits_29 / 10;
constexpr unsigned __int128 digits_27 = digits_28 / 10;
constexpr unsigned __int128 digits_26 = digits_27 / 10;
constexpr unsigned __int128 digits_25 = digits_26 / 10;
constexpr unsigned __int128 digits_24 = digits_25 / 10;
constexpr unsigned __int128 digits_23 = digits_24 / 10;
constexpr unsigned __int128 digits_22 = digits_23 / 10;
constexpr unsigned __int128 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 // 128-bit support
#endif // BOOST_CHARCONV_DETAIL_INTEGER_SEARCH_TREES_HPP

1
include/boost/charconv/to_chars.hpp
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@@ -6,6 +6,7 @@
#ifndef BOOST_CHARCONV_TO_CHARS_HPP_INCLUDED
#define BOOST_CHARCONV_TO_CHARS_HPP_INCLUDED
#include <boost/charconv/detail/integer_search_trees.hpp>
#include <boost/charconv/config.hpp>
#include <type_traits>
#include <array>