1// Copyright (c) 2021-present The Bitcoin Core developers
2// Distributed under the MIT software license, see the accompanying
3// file COPYING or http://www.opensource.org/licenses/mit-license.php.
4
5#include <util/serfloat.h>
6
7#include <cmath>
8#include <limits>
9
10double DecodeDouble(uint64_t v) noexcept {
11    static constexpr double NANVAL = std::numeric_limits<double>::quiet_NaN();
12    static constexpr double INFVAL = std::numeric_limits<double>::infinity();
13    double sign = 1.0;
14    if (v & 0x8000000000000000) {
15        sign = -1.0;
16        v ^= 0x8000000000000000;
17    }
18    // Zero
19    if (v == 0) return copysign(0.0, sign);
20    // Infinity
21    if (v == 0x7ff0000000000000) return copysign(INFVAL, sign);
22    // Other numbers
23    int exp = (v & 0x7FF0000000000000) >> 52;
24    uint64_t man = v & 0xFFFFFFFFFFFFF;
25    if (exp == 2047) {
26        // NaN
27        return NANVAL;
28    } else if (exp == 0) {
29        // Subnormal
30        return copysign(ldexp((double)man, -1074), sign);
31    } else {
32        // Normal
33        return copysign(ldexp((double)(man + 0x10000000000000), -1075 + exp), sign);
34    }
35}
36
37uint64_t EncodeDouble(double f) noexcept {
38    int cls = std::fpclassify(f);
39    uint64_t sign = 0;
40    if (copysign(1.0, f) == -1.0) {
41        f = -f;
42        sign = 0x8000000000000000;
43    }
44    // Zero
45    if (cls == FP_ZERO) return sign;
46    // Infinity
47    if (cls == FP_INFINITE) return sign | 0x7ff0000000000000;
48    // NaN
49    if (cls == FP_NAN) return 0x7ff8000000000000;
50    // Other numbers
51    int exp;
52    uint64_t man = std::round(std::frexp(f, &exp) * 9007199254740992.0);
53    if (exp < -1021) {
54        // Too small to represent, encode 0
55        if (exp < -1084) return sign;
56        // Subnormal numbers
57        return sign | (man >> (-1021 - exp));
58    } else {
59        // Too big to represent, encode infinity
60        if (exp > 1024) return sign | 0x7ff0000000000000;
61        // Normal numbers
62        return sign | (((uint64_t)(1022 + exp)) << 52) | (man & 0xFFFFFFFFFFFFF);
63    }
64}
65