1  // Copyright (c) 2021 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  
10  double 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  
37  uint64_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  }