// Copyright (c) 2024 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/feefrac.h>

#include <test/fuzz/FuzzedDataProvider.h>

#include <test/fuzz/fuzz.h>

#include <test/fuzz/util.h>

#include <compare>

#include <cstdint>

#include <iostream>

namespace {

/** Compute a * b, represented in 4x32 bits, highest limb first. */

std::array<uint32_t, 4> Mul128(uint64_t a, uint64_t b)

{

    std::array<uint32_t, 4> ret{0, 0, 0, 0};

    /** Perform ret += v << (32 * pos), at 128-bit precision. */

    auto add_fn = [&](uint64_t v, int pos) {

        uint64_t accum{0};

        for (int i = 0; i + pos < 4; ++i) {

            // Add current value at limb pos in ret.

            accum += ret[3 - pos - i];

            // Add low or high half of v.

            if (i == 0) accum += v & 0xffffffff;

            if (i == 1) accum += v >> 32;

            // Store lower half of result in limb pos in ret.

            ret[3 - pos - i] = accum & 0xffffffff;

            // Leave carry in accum.

            accum >>= 32;

        }

        // Make sure no overflow.

        assert(accum == 0);

    };

    // Multiply the 4 individual limbs (schoolbook multiply, with base 2^32).

    add_fn((a & 0xffffffff) * (b & 0xffffffff), 0);

    add_fn((a >> 32) * (b & 0xffffffff), 1);

    add_fn((a & 0xffffffff) * (b >> 32), 1);

    add_fn((a >> 32) * (b >> 32), 2);

    return ret;

}

/* comparison helper for std::array */

std::strong_ordering compare_arrays(const std::array<uint32_t, 4>& a, const std::array<uint32_t, 4>& b) {

    for (size_t i = 0; i < a.size(); ++i) {

        if (a[i] != b[i]) return a[i] <=> b[i];

    }

    return std::strong_ordering::equal;

}

std::strong_ordering MulCompare(int64_t a1, int64_t a2, int64_t b1, int64_t b2)

{

    // Compute and compare signs.

    int sign_a = (a1 == 0 ? 0 : a1 < 0 ? -1 : 1) * (a2 == 0 ? 0 : a2 < 0 ? -1 : 1);

    int sign_b = (b1 == 0 ? 0 : b1 < 0 ? -1 : 1) * (b2 == 0 ? 0 : b2 < 0 ? -1 : 1);

    if (sign_a != sign_b) return sign_a <=> sign_b;

    // Compute absolute values.

    uint64_t abs_a1 = static_cast<uint64_t>(a1), abs_a2 = static_cast<uint64_t>(a2);

    uint64_t abs_b1 = static_cast<uint64_t>(b1), abs_b2 = static_cast<uint64_t>(b2);

    // Use (~x + 1) instead of the equivalent (-x) to silence the linter; mod 2^64 behavior is

    // intentional here.

    if (a1 < 0) abs_a1 = ~abs_a1 + 1;

    if (a2 < 0) abs_a2 = ~abs_a2 + 1;

    if (b1 < 0) abs_b1 = ~abs_b1 + 1;

    if (b2 < 0) abs_b2 = ~abs_b2 + 1;

    // Compute products of absolute values.

    auto mul_abs_a = Mul128(abs_a1, abs_a2);

    auto mul_abs_b = Mul128(abs_b1, abs_b2);

    if (sign_a < 0) {

        return compare_arrays(mul_abs_b, mul_abs_a);

    } else {

        return compare_arrays(mul_abs_a, mul_abs_b);

    }

}

} // namespace

FUZZ_TARGET(feefrac)

{

    FuzzedDataProvider provider(buffer.data(), buffer.size());

    int64_t f1 = provider.ConsumeIntegral<int64_t>();

    int32_t s1 = provider.ConsumeIntegral<int32_t>();

    if (s1 == 0) f1 = 0;

    FeeFrac fr1(f1, s1);

    assert(fr1.IsEmpty() == (s1 == 0));

    int64_t f2 = provider.ConsumeIntegral<int64_t>();

    int32_t s2 = provider.ConsumeIntegral<int32_t>();

    if (s2 == 0) f2 = 0;

    FeeFrac fr2(f2, s2);

    assert(fr2.IsEmpty() == (s2 == 0));

    // Feerate comparisons

    auto cmp_feerate = MulCompare(f1, s2, f2, s1);

    assert(FeeRateCompare(fr1, fr2) == cmp_feerate);

    assert((fr1 << fr2) == std::is_lt(cmp_feerate));

    assert((fr1 >> fr2) == std::is_gt(cmp_feerate));

    // Compare with manual invocation of FeeFrac::Mul.

    auto cmp_mul = FeeFrac::Mul(f1, s2) <=> FeeFrac::Mul(f2, s1);

    assert(cmp_mul == cmp_feerate);

    // Same, but using FeeFrac::MulFallback.

    auto cmp_fallback = FeeFrac::MulFallback(f1, s2) <=> FeeFrac::MulFallback(f2, s1);

    assert(cmp_fallback == cmp_feerate);

    // Total order comparisons

    auto cmp_total = std::is_eq(cmp_feerate) ? (s2 <=> s1) : cmp_feerate;

    assert((fr1 <=> fr2) == cmp_total);

    assert((fr1 < fr2) == std::is_lt(cmp_total));

    assert((fr1 > fr2) == std::is_gt(cmp_total));

    assert((fr1 <= fr2) == std::is_lteq(cmp_total));

    assert((fr1 >= fr2) == std::is_gteq(cmp_total));

    assert((fr1 == fr2) == std::is_eq(cmp_total));

    assert((fr1 != fr2) == std::is_neq(cmp_total));

}