// Copyright (c) 2021-present The Bitcoin Core developers

// Distributed under the MIT software license, see the accompanying

// file COPYING or http://www.opensource.org/licenses/mit-license.php.

#include <util/serfloat.h>

#include <cmath>

#include <limits>

double DecodeDouble(uint64_t v) noexcept {

    static constexpr double NANVAL = std::numeric_limits<double>::quiet_NaN();

    static constexpr double INFVAL = std::numeric_limits<double>::infinity();

    double sign = 1.0;

    if (v & 0x8000000000000000) {

        sign = -1.0;

        v ^= 0x8000000000000000;

    }

    // Zero

    if (v == 0) return copysign(0.0, sign);

    // Infinity

    if (v == 0x7ff0000000000000) return copysign(INFVAL, sign);

    // Other numbers

    int exp = (v & 0x7FF0000000000000) >> 52;

    uint64_t man = v & 0xFFFFFFFFFFFFF;

    if (exp == 2047) {

        // NaN

        return NANVAL;

    } else if (exp == 0) {

        // Subnormal

        return copysign(ldexp((double)man, -1074), sign);

    } else {

        // Normal

        return copysign(ldexp((double)(man + 0x10000000000000), -1075 + exp), sign);

    }

}

uint64_t EncodeDouble(double f) noexcept {

    int cls = std::fpclassify(f);

    uint64_t sign = 0;

    if (copysign(1.0, f) == -1.0) {

        f = -f;

        sign = 0x8000000000000000;

    }

    // Zero

    if (cls == FP_ZERO) return sign;

    // Infinity

    if (cls == FP_INFINITE) return sign | 0x7ff0000000000000;

    // NaN

    if (cls == FP_NAN) return 0x7ff8000000000000;

    // Other numbers

    int exp;

    uint64_t man = std::round(std::frexp(f, &exp) * 9007199254740992.0);

    if (exp < -1021) {

        // Too small to represent, encode 0

        if (exp < -1084) return sign;

        // Subnormal numbers

        return sign | (man >> (-1021 - exp));

    } else {

        // Too big to represent, encode infinity

        if (exp > 1024) return sign | 0x7ff0000000000000;

        // Normal numbers

        return sign | (((uint64_t)(1022 + exp)) << 52) | (man & 0xFFFFFFFFFFFFF);

    }

}