partial bitcoin#21966: Add platform-independent float encoder/decoder

This commit is contained in:
Kittywhiskers Van Gogh 2021-06-16 14:13:28 +05:30
parent 4d6d3eb5a7
commit f946c68f83
3 changed files with 82 additions and 0 deletions

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@ -268,6 +268,7 @@ BITCOIN_CORE_H = \
util/macros.h \
util/memory.h \
util/moneystr.h \
util/serfloat.h \
util/string.h \
util/time.h \
util/threadnames.h \
@ -605,6 +606,7 @@ libdash_util_a_SOURCES = \
util/moneystr.cpp \
util/strencodings.cpp \
util/time.cpp \
util/serfloat.cpp \
util/string.cpp \
util/threadnames.cpp \
util/url.cpp \

64
src/util/serfloat.cpp Normal file
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@ -0,0 +1,64 @@
// Copyright (c) 2021 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);
}
}

16
src/util/serfloat.h Normal file
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@ -0,0 +1,16 @@
// Copyright (c) 2021 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#ifndef BITCOIN_UTIL_SERFLOAT_H
#define BITCOIN_UTIL_SERFLOAT_H
#include <stdint.h>
/* Encode a double using the IEEE 754 binary64 format. All NaNs are encoded as x86/ARM's
* positive quiet NaN with payload 0. */
uint64_t EncodeDouble(double f) noexcept;
/* Reverse operation of DecodeDouble. DecodeDouble(EncodeDouble(f))==f unless isnan(f). */
double DecodeDouble(uint64_t v) noexcept;
#endif // BITCOIN_UTIL_SERFLOAT_H