json/include/nlohmann/detail/view/number.hpp

//     __ _____ _____ _____
//  __|  |   __|     |   | |  JSON for Modern C++
// |  |  |__   |  |  | | | |  version 3.12.0
// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
//
// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
// SPDX-License-Identifier: MIT

#pragma once

#include <array> // array
#include <cfloat> // FLT_EVAL_METHOD
#include <cstddef> // size_t
#include <cstdint> // int64_t, uint64_t
#include <cstring> // memcpy
#include <string> // string
#include <type_traits> // integral_constant, is_same

#include <nlohmann/json.hpp>
#include <nlohmann/detail/view/document_data.hpp>
#include <nlohmann/detail/view/macro_scope.hpp>
#include <nlohmann/detail/view/node.hpp>
#include <nlohmann/detail/view/scan.hpp>

NLOHMANN_JSON_NAMESPACE_BEGIN
namespace detail
{
namespace view
{

/*!
@brief the value of the float token of a node, as parse() converts it

Uses the lexer's conversion (detail::convert_float_fast, then the locale-aware
strtod fallback), so that the values are bit-identical to parse(). The digit
layout recorded while parsing locates the decimal point and the exponent
without scanning the token.
*/
template<typename FloatType>
NLOHMANN_VIEW_NOINLINE FloatType float_value(const char* first, const node& n)
{
    const char* const last = first + n.len;
    const std::size_t neg = first[0] == '-' ? 1 : 0;
    const std::size_t int_digits = n.extra & 0xFFu;
    const std::size_t frac_digits = n.extra >> 8u;
    std::size_t dot = std::string::npos;
    std::size_t mantissa_end = n.len;
    if (int_digits != 255 && frac_digits != 255)
    {
        dot = frac_digits != 0 ? neg + int_digits : std::string::npos;
        mantissa_end = neg + int_digits + (frac_digits != 0 ? 1 + frac_digits : 0);
    }
    else
    {
        // more digits than the layout records: locate them
        for (std::size_t i = 0; i < n.len; ++i)
        {
            if (first[i] == '.')
            {
                dot = i;
            }
            else if (first[i] == 'e' || first[i] == 'E')
            {
                mantissa_end = i;
                break;
            }
        }
    }
    FloatType v{};
    if (!convert_float_fast(first, last, dot, mantissa_end, v))
    {
        std::string token(first, last);
        convert_float_locale_aware(token, dot, v);
    }
    return v;
}

/*!
@brief the double of a float token with at most 19 digits, from its layout

The digit layout recorded while parsing says where the integer digits, the
fraction digits, and the exponent are, so the digits are read eight at a
time without scanning. The result is correctly rounded (Clinger's fast path
where both operands are exact, else the Eisel-Lemire algorithm, which needs
no fallback for up to 19 digits), so it is the value parse() produces.

@param[in] p  first character of the token
@param[in] e  end of the token
@param[in] limit  end of the readable memory (the source text)
*/
NLOHMANN_VIEW_ALWAYS_INLINE double layout_double(const unsigned char* p, const unsigned char* e, unsigned int_digits, unsigned frac_digits, const unsigned char* limit) noexcept
{
    const bool negative = *p == '-';
    p += negative ? 1 : 0;
    std::uint64_t w = parse_upto19(p, int_digits, limit);
    p += int_digits;
    std::int64_t q = 0;
    if (frac_digits != 0)
    {
        w = (w * int_pow10(frac_digits)) + parse_upto19(p + 1, frac_digits, limit);
        p += 1 + frac_digits;
        q = -static_cast<std::int64_t>(frac_digits);
    }
    if (p != e)
    {
        // [eE][+-]digits; huge exponents saturate (the parser rejected overflow)
        ++p;
        const bool exp_negative = *p == '-';
        p += (*p == '-' || *p == '+') ? 1 : 0;
        std::int64_t exp_value = 0;
        for (; p != e; ++p)
        {
            if (exp_value < 0x10000000)
            {
                exp_value = (exp_value * 10) + (*p - '0');
            }
        }
        q += exp_negative ? -exp_value : exp_value;
    }

    double result = 0;
    if (w != 0)
    {
#if !defined(FLT_EVAL_METHOD) || FLT_EVAL_METHOD == 0
        static const std::array<double, 23> pow10 = {{1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9, 1e10, 1e11, 1e12, 1e13, 1e14, 1e15, 1e16, 1e17, 1e18, 1e19, 1e20, 1e21, 1e22}};
        if (q >= -22 && q <= 22 && w <= (std::uint64_t{1} << 53))
        {
            // Clinger's fast path: both operands exact, one rounding
            result = static_cast<double>(w);
            result = q < 0 ? result / pow10[static_cast<std::size_t>(-q)] : result * pow10[static_cast<std::size_t>(q)];
            return negative ? -result : result;
        }
#endif
        const std::uint64_t bits = eisel_lemire(q, w);
        std::memcpy(&result, &bits, sizeof(result));
    }
    return negative ? -result : result;
}

/// the value of the float token of a node, as parse() converts it; doubles
/// with at most 19 digits are converted from the digit layout
template<typename FloatType>
FloatType float_value(const document_data& d, const node& n)
{
    return float_value<FloatType>(d, n, std::is_same<FloatType, double> {});
}

template<typename FloatType>
FloatType float_value(const document_data& d, const node& n, std::true_type /*double*/)
{
    const unsigned int_digits = n.extra & 0xFFu;
    const unsigned frac_digits = n.extra >> 8u;
    if (NLOHMANN_VIEW_LIKELY(int_digits + frac_digits <= 19)) // (255 marks "many")
    {
        // (a float token not written by an edit is in the text)
        const auto* const first = reinterpret_cast<const unsigned char*>(d.src + n.off); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
        return layout_double(first, first + n.len, int_digits, frac_digits, reinterpret_cast<const unsigned char*>(d.src + d.size)); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
    }
    return float_value<FloatType>(d.str(n), n);
}

template<typename FloatType>
FloatType float_value(const document_data& d, const node& n, std::false_type /*other*/)
{
    return float_value<FloatType>(d.str(n), n);
}

}  // namespace view
}  // namespace detail
NLOHMANN_JSON_NAMESPACE_END