Function format_buffer

3rd/nlohmann_json/single_include/nlohmann/json.hpp:16294–16362

JSON_HEDLEY_NON_NULL(1)
JSON_HEDLEY_RETURNS_NON_NULL
inline char* format_buffer(char* buf, int len, int decimal_exponent,
                           int min_exp, int max_exp)
{
    JSON_ASSERT(min_exp < 0);
    JSON_ASSERT(max_exp > 0);

    const int k = len;
    const int n = len + decimal_exponent;

    // v = buf * 10^(n-k)
    // k is the length of the buffer (number of decimal digits)
    // n is the position of the decimal point relative to the start of the buffer.

    if (k <= n && n <= max_exp)
    {
        // digits[000]
        // len <= max_exp + 2

        std::memset(buf + k, '0', static_cast<size_t>(n) - static_cast<size_t>(k));
        // Make it look like a floating-point number (#362, #378)
        buf[n + 0] = '.';
        buf[n + 1] = '0';
        return buf + (static_cast<size_t>(n) + 2);
    }

    if (0 < n && n <= max_exp)
    {
        // dig.its
        // len <= max_digits10 + 1

        JSON_ASSERT(k > n);

        std::memmove(buf + (static_cast<size_t>(n) + 1), buf + n, static_cast<size_t>(k) - static_cast<size_t>(n));
        buf[n] = '.';
        return buf + (static_cast<size_t>(k) + 1U);
    }

    if (min_exp < n && n <= 0)
    {
        // 0.[000]digits
        // len <= 2 + (-min_exp - 1) + max_digits10

        std::memmove(buf + (2 + static_cast<size_t>(-n)), buf, static_cast<size_t>(k));
        buf[0] = '0';
        buf[1] = '.';
        std::memset(buf + 2, '0', static_cast<size_t>(-n));
        return buf + (2U + static_cast<size_t>(-n) + static_cast<size_t>(k));
    }

    if (k == 1)
    {
        // dE+123
        // len <= 1 + 5

        buf += 1;
    }
    else
    {