serfloat_tests.cpp

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// Copyright (c) 2014-2021 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 <hash.h>
#include <test/util/random.h>
#include <test/util/setup_common.h>
#include <util/serfloat.h>
#include <serialize.h>
#include <streams.h>

#include <boost/test/unit_test.hpp>

#include <cmath>
#include <limits>

BOOST_FIXTURE_TEST_SUITE(serfloat_tests, BasicTestingSetup)

namespace {

uint64_t TestDouble(double f) {
    uint64_t i = EncodeDouble(f);
    double f2 = DecodeDouble(i);
    if (std::isnan(f)) {
        // NaN is not guaranteed to round-trip exactly.
        BOOST_CHECK(std::isnan(f2));
    } else {
        // Everything else is.
        BOOST_CHECK(!std::isnan(f2));
        uint64_t i2 = EncodeDouble(f2);
        BOOST_CHECK_EQUAL(f, f2);
        BOOST_CHECK_EQUAL(i, i2);
    }
    return i;
}

} // namespace

BOOST_AUTO_TEST_CASE(double_serfloat_tests) {
    BOOST_CHECK_EQUAL(TestDouble(0.0), 0U);
    BOOST_CHECK_EQUAL(TestDouble(-0.0), 0x8000000000000000);
    BOOST_CHECK_EQUAL(TestDouble(std::numeric_limits<double>::infinity()), 0x7ff0000000000000U);
    BOOST_CHECK_EQUAL(TestDouble(-std::numeric_limits<double>::infinity()), 0xfff0000000000000);
    BOOST_CHECK_EQUAL(TestDouble(0.5), 0x3fe0000000000000ULL);
    BOOST_CHECK_EQUAL(TestDouble(1.0), 0x3ff0000000000000ULL);
    BOOST_CHECK_EQUAL(TestDouble(2.0), 0x4000000000000000ULL);
    BOOST_CHECK_EQUAL(TestDouble(4.0), 0x4010000000000000ULL);
    BOOST_CHECK_EQUAL(TestDouble(785.066650390625), 0x4088888880000000ULL);

    // Roundtrip test on IEC559-compatible systems
    if (std::numeric_limits<double>::is_iec559) {
        BOOST_CHECK_EQUAL(sizeof(double), 8U);
        BOOST_CHECK_EQUAL(sizeof(uint64_t), 8U);
        // Test extreme values
        TestDouble(std::numeric_limits<double>::min());
        TestDouble(-std::numeric_limits<double>::min());
        TestDouble(std::numeric_limits<double>::max());
        TestDouble(-std::numeric_limits<double>::max());
        TestDouble(std::numeric_limits<double>::lowest());
        TestDouble(-std::numeric_limits<double>::lowest());
        TestDouble(std::numeric_limits<double>::quiet_NaN());
        TestDouble(-std::numeric_limits<double>::quiet_NaN());
        TestDouble(std::numeric_limits<double>::signaling_NaN());
        TestDouble(-std::numeric_limits<double>::signaling_NaN());
        TestDouble(std::numeric_limits<double>::denorm_min());
        TestDouble(-std::numeric_limits<double>::denorm_min());
        // Test exact encoding: on currently supported platforms, EncodeDouble
        // should produce exactly the same as the in-memory representation for non-NaN.
        for (int j = 0; j < 1000; ++j) {
            // Iterate over 9 specific bits exhaustively; the others are chosen randomly.
            // These specific bits are the sign bit, and the 2 top and bottom bits of
            // exponent and mantissa in the IEEE754 binary64 format.
            for (int x = 0; x < 512; ++x) {
                uint64_t v = InsecureRandBits(64);
                v &= ~(uint64_t{1} << 0);
                if (x & 1) v |= (uint64_t{1} << 0);
                v &= ~(uint64_t{1} << 1);
                if (x & 2) v |= (uint64_t{1} << 1);
                v &= ~(uint64_t{1} << 50);
                if (x & 4) v |= (uint64_t{1} << 50);
                v &= ~(uint64_t{1} << 51);
                if (x & 8) v |= (uint64_t{1} << 51);
                v &= ~(uint64_t{1} << 52);
                if (x & 16) v |= (uint64_t{1} << 52);
                v &= ~(uint64_t{1} << 53);
                if (x & 32) v |= (uint64_t{1} << 53);
                v &= ~(uint64_t{1} << 61);
                if (x & 64) v |= (uint64_t{1} << 61);
                v &= ~(uint64_t{1} << 62);
                if (x & 128) v |= (uint64_t{1} << 62);
                v &= ~(uint64_t{1} << 63);
                if (x & 256) v |= (uint64_t{1} << 63);
                double f;
                memcpy(&f, &v, 8);
                uint64_t v2 = TestDouble(f);
                if (!std::isnan(f)) BOOST_CHECK_EQUAL(v, v2);
            }
        }
    }
}

/*
Python code to generate the below hashes:

    def reversed_hex(x):
        return bytes(reversed(x)).hex()

    def dsha256(x):
        return hashlib.sha256(hashlib.sha256(x).digest()).digest()

    reversed_hex(dsha256(b''.join(struct.pack('<d', x) for x in range(0,1000)))) == '43d0c82591953c4eafe114590d392676a01585d25b25d433557f0d7878b23f96'
*/
BOOST_AUTO_TEST_CASE(doubles)
{
    DataStream ss{};
    // encode
    for (int i = 0; i < 1000; i++) {
        ss << EncodeDouble(i);
    }
    BOOST_CHECK(Hash(ss) == uint256S("43d0c82591953c4eafe114590d392676a01585d25b25d433557f0d7878b23f96"));

    // decode
    for (int i = 0; i < 1000; i++) {
        uint64_t val;
        ss >> val;
        double j = DecodeDouble(val);
        BOOST_CHECK_MESSAGE(i == j, "decoded:" << j << " expected:" << i);
    }
}

BOOST_AUTO_TEST_SUITE_END()