json/include/nlohmann/detail/output/denumerizer.hpp

#pragma once

#include <algorithm> // reverse, remove, fill, find, none_of
#include <array> // array
#include <clocale> // localeconv, lconv
#include <cmath> // labs, isfinite, isnan, signbit
#include <cstddef> // size_t, ptrdiff_t
#include <cstdio> // snprintf
#include <limits> // numeric_limits
#include <string> // char_traits

#include <nlohmann/detail/conversions/to_chars.hpp>
#include <nlohmann/detail/macro_scope.hpp>
#include <nlohmann/detail/meta/cpp_future.hpp>

namespace nlohmann
{
namespace detail
{

struct denumerizer
{
    using number_buffer_t = std::array<char, 64>;

    /*!
    @brief count digits
    Count the number of decimal (base 10) digits for an input unsigned integer.
    @param[in] x  unsigned integer number to count its digits
    @return    number of decimal digits
    */
    template <typename number_unsigned_t>
    static unsigned int count_digits(number_unsigned_t x) noexcept
    {
        unsigned int n_digits = 1;
        for (;;)
        {
            if (x < 10)
            {
                return n_digits;
            }
            if (x < 100)
            {
                return n_digits + 1;
            }
            if (x < 1000)
            {
                return n_digits + 2;
            }
            if (x < 10000)
            {
                return n_digits + 3;
            }
            x = static_cast<number_unsigned_t>(x / 10000u);
            n_digits += 4;
        }
    }

    /*
     * Overload to make the compiler happy while it is instantiating
     * dump_integer for number_unsigned_t.
     * Must never be called.
     */
    template <typename number_unsigned_t,
              detail::enable_if_t<
                  std::is_unsigned<number_unsigned_t>::value, int> = 0>
    static number_unsigned_t remove_sign(number_unsigned_t x) noexcept
    {
        JSON_ASSERT(false); // NOLINT(cert-dcl03-c,hicpp-static-assert,misc-static-assert) LCOV_EXCL_LINE
        return x; // LCOV_EXCL_LINE
    }

    /*
     * Helper function for dump_integer
     *
     * This function takes a negative signed integer and returns its absolute
     * value as unsigned integer. The plus/minus shuffling is necessary as we can
     * not directly remove the sign of an arbitrary signed integer as the
     * absolute values of INT_MIN and INT_MAX are usually not the same. See
     * #1708 for details.
     */
    template <typename number_integer_t,
              detail::enable_if_t<
                  std::is_signed<number_integer_t>::value, int> = 0,
              typename number_unsigned_t =
              typename std::make_unsigned<number_integer_t>::type>
    static number_unsigned_t remove_sign(number_integer_t x) noexcept
    {
        JSON_ASSERT(x < 0 && x < (std::numeric_limits<number_integer_t>::max)()); // NOLINT(misc-redundant-expression)
        return static_cast<number_unsigned_t>(-(x + 1)) + 1;
    }

    /*!
    @brief dump an integer
    Dump a given integer to output stream @a o.
    @param[in] x  integer number (signed or unsigned) to dump
    */
    template <typename OutputAdapterType, typename number_integral_t,
              typename number_unsigned_t = typename std::make_unsigned<
                  number_integral_t>::type>
    static void dump_integer(OutputAdapterType& o, number_integral_t x)
    {
        static constexpr std::array<std::array<char, 2>, 100> digits_to_99
        {
            {
                {{'0', '0'}}, {{'0', '1'}}, {{'0', '2'}}, {{'0', '3'}}, {{'0', '4'}}, {{'0', '5'}}, {{'0', '6'}}, {{'0', '7'}}, {{'0', '8'}}, {{'0', '9'}},
                {{'1', '0'}}, {{'1', '1'}}, {{'1', '2'}}, {{'1', '3'}}, {{'1', '4'}}, {{'1', '5'}}, {{'1', '6'}}, {{'1', '7'}}, {{'1', '8'}}, {{'1', '9'}},
                {{'2', '0'}}, {{'2', '1'}}, {{'2', '2'}}, {{'2', '3'}}, {{'2', '4'}}, {{'2', '5'}}, {{'2', '6'}}, {{'2', '7'}}, {{'2', '8'}}, {{'2', '9'}},
                {{'3', '0'}}, {{'3', '1'}}, {{'3', '2'}}, {{'3', '3'}}, {{'3', '4'}}, {{'3', '5'}}, {{'3', '6'}}, {{'3', '7'}}, {{'3', '8'}}, {{'3', '9'}},
                {{'4', '0'}}, {{'4', '1'}}, {{'4', '2'}}, {{'4', '3'}}, {{'4', '4'}}, {{'4', '5'}}, {{'4', '6'}}, {{'4', '7'}}, {{'4', '8'}}, {{'4', '9'}},
                {{'5', '0'}}, {{'5', '1'}}, {{'5', '2'}}, {{'5', '3'}}, {{'5', '4'}}, {{'5', '5'}}, {{'5', '6'}}, {{'5', '7'}}, {{'5', '8'}}, {{'5', '9'}},
                {{'6', '0'}}, {{'6', '1'}}, {{'6', '2'}}, {{'6', '3'}}, {{'6', '4'}}, {{'6', '5'}}, {{'6', '6'}}, {{'6', '7'}}, {{'6', '8'}}, {{'6', '9'}},
                {{'7', '0'}}, {{'7', '1'}}, {{'7', '2'}}, {{'7', '3'}}, {{'7', '4'}}, {{'7', '5'}}, {{'7', '6'}}, {{'7', '7'}}, {{'7', '8'}}, {{'7', '9'}},
                {{'8', '0'}}, {{'8', '1'}}, {{'8', '2'}}, {{'8', '3'}}, {{'8', '4'}}, {{'8', '5'}}, {{'8', '6'}}, {{'8', '7'}}, {{'8', '8'}}, {{'8', '9'}},
                {{'9', '0'}}, {{'9', '1'}}, {{'9', '2'}}, {{'9', '3'}}, {{'9', '4'}}, {{'9', '5'}}, {{'9', '6'}}, {{'9', '7'}}, {{'9', '8'}}, {{'9', '9'}},
            }
        };

        // special case for "0"
        if (x == 0)
        {
            o->write_character('0');
            return;
        }

        number_buffer_t number_buffer{{}};

        // use a pointer to fill the buffer
        auto buffer_ptr = number_buffer.begin(); // NOLINT(llvm-qualified-auto,readability-qualified-auto,cppcoreguidelines-pro-type-vararg,hicpp-vararg)

        const bool is_negative = std::is_signed<number_integral_t>::value && !(x >= 0); // see issue #755
        number_unsigned_t abs_value;

        unsigned int n_chars{};

        if (is_negative)
        {
            *buffer_ptr = '-';
            abs_value = remove_sign(static_cast<number_integral_t>(x));

            // account one more byte for the minus sign
            n_chars = 1 + count_digits(abs_value);
        }
        else
        {
            abs_value = static_cast<number_unsigned_t>(x);
            n_chars = count_digits(abs_value);
        }

        // spare 1 byte for '\0'
        JSON_ASSERT(n_chars < number_buffer.size() - 1);

        // jump to the end to generate the string from backward
        // so we later avoid reversing the result
        buffer_ptr += n_chars;

        // Fast int2ascii implementation inspired by "Fastware" talk by Andrei Alexandrescu
        // See: https://www.youtube.com/watch?v=o4-CwDo2zpg
        while (abs_value >= 100)
        {
            const auto digits_index = static_cast<unsigned>((abs_value % 100));
            abs_value /= 100;
            *(--buffer_ptr) = digits_to_99[digits_index][1];
            *(--buffer_ptr) = digits_to_99[digits_index][0];
        }

        if (abs_value >= 10)
        {
            const auto digits_index = static_cast<unsigned>(abs_value);
            *(--buffer_ptr) = digits_to_99[digits_index][1];
            *(--buffer_ptr) = digits_to_99[digits_index][0];
        }
        else
        {
            *(--buffer_ptr) = static_cast<char>('0' + abs_value);
        }

        o->write_characters(number_buffer.data(), n_chars);
    }

    /*!
    @brief dump a floating-point number
    Dump a given floating-point number to output stream @a o.
    @param[in] x  floating-point number to dump
    */
    template <typename OutputAdapterType, typename number_float_t,
              detail::enable_if_t<
                  std::is_floating_point<number_float_t>::value, int> = 0>
    static void dump_float(OutputAdapterType& o, number_float_t x)
    {
        // NaN / inf
        if (!std::isfinite(x))
        {
            o->write_characters("null", 4);
            return;
        }

        // If number_float_t is an IEEE-754 single or double precision number,
        // use the Grisu2 algorithm to produce short numbers which are
        // guaranteed to round-trip, using strtof and strtod, resp.
        //
        // NB: The test below works if <long double> == <double>.
        static constexpr bool is_ieee_single_or_double
            = (std::numeric_limits<number_float_t>::is_iec559 && std::numeric_limits<number_float_t>::digits == 24 && std::numeric_limits<number_float_t>::max_exponent == 128) ||
              (std::numeric_limits<number_float_t>::is_iec559 && std::numeric_limits<number_float_t>::digits == 53 && std::numeric_limits<number_float_t>::max_exponent == 1024);

        dump_float(o, x, std::integral_constant<bool, is_ieee_single_or_double>());
    }

    template <typename OutputAdapterType, typename number_float_t,
              detail::enable_if_t<
                  std::is_floating_point<number_float_t>::value, int> = 0>
    static void dump_float(OutputAdapterType& o, number_float_t x, std::true_type /*is_ieee_single_or_double*/)
    {
        number_buffer_t number_buffer{{}};

        auto* begin = number_buffer.data();
        auto* end = ::nlohmann::detail::to_chars(begin, begin + number_buffer.size(), x);

        o->write_characters(begin, static_cast<size_t>(end - begin));
    }

    template <typename OutputAdapterType, typename number_float_t,
              detail::enable_if_t<
                  std::is_floating_point<number_float_t>::value, int> = 0>
    static void dump_float(OutputAdapterType& o, number_float_t x, std::false_type /*is_ieee_single_or_double*/)
    {
        number_buffer_t number_buffer{{}};

        const std::lconv* loc(std::localeconv());
        const char thousands_sep(loc->thousands_sep == nullptr ? '\0' : std::char_traits<char>::to_char_type(* (loc->thousands_sep)));
        const char decimal_point(loc->decimal_point == nullptr ? '\0' : std::char_traits<char>::to_char_type(* (loc->decimal_point)));

        // get number of digits for a float -> text -> float round-trip
        static constexpr auto d = std::numeric_limits<number_float_t>::max_digits10;

        // the actual conversion
        // NOLINTNEXTLINE(cppcoreguidelines-pro-type-vararg,hicpp-vararg)
        std::ptrdiff_t len = (std::snprintf)(number_buffer.data(), number_buffer.size(), "%.*g", d, x);

        // negative value indicates an error
        JSON_ASSERT(len > 0);
        // check if buffer was large enough
        JSON_ASSERT(static_cast<std::size_t>(len) < number_buffer.size());

        // erase thousands separator
        if (thousands_sep != '\0')
        {
            // NOLINTNEXTLINE(readability-qualified-auto,llvm-qualified-auto): std::remove returns an iterator, see https://github.com/nlohmann/json/issues/3081
            const auto end = std::remove(number_buffer.begin(), number_buffer.begin() + len, thousands_sep);
            std::fill(end, number_buffer.end(), '\0');
            JSON_ASSERT((end - number_buffer.begin()) <= len);
            len = (end - number_buffer.begin());
        }

        // convert decimal point to '.'
        if (decimal_point != '\0' && decimal_point != '.')
        {
            // NOLINTNEXTLINE(readability-qualified-auto,llvm-qualified-auto): std::find returns an iterator, see https://github.com/nlohmann/json/issues/3081
            const auto dec_pos = std::find(number_buffer.begin(), number_buffer.end(), decimal_point);
            if (dec_pos != number_buffer.end())
            {
                *dec_pos = '.';
            }
        }

        o->write_characters(number_buffer.data(), static_cast<std::size_t>(len));

        // determine if need to append ".0"
        const bool value_is_int_like =
            std::none_of(number_buffer.begin(), number_buffer.begin() + len + 1,
                         [](char c)
        {
            return c == '.' || c == 'e';
        });

        if (value_is_int_like)
        {
            o->write_characters(".0", 2);
        }
    }
};

}  // namespace detail
}  // namespace nlohmann