feefrac.cpp raw
1 // Copyright (c) 2024 The Limenka 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/feefrac.h>
6 #include <test/fuzz/FuzzedDataProvider.h>
7 #include <test/fuzz/fuzz.h>
8 #include <test/fuzz/util.h>
9
10 #include <compare>
11 #include <cstdint>
12 #include <iostream>
13
14 namespace {
15
16 /** Compute a * b, represented in 4x32 bits, highest limb first. */
17 std::array<uint32_t, 4> Mul128(uint64_t a, uint64_t b)
18 {
19 std::array<uint32_t, 4> ret{0, 0, 0, 0};
20
21 /** Perform ret += v << (32 * pos), at 128-bit precision. */
22 auto add_fn = [&](uint64_t v, int pos) {
23 uint64_t accum{0};
24 for (int i = 0; i + pos < 4; ++i) {
25 // Add current value at limb pos in ret.
26 accum += ret[3 - pos - i];
27 // Add low or high half of v.
28 if (i == 0) accum += v & 0xffffffff;
29 if (i == 1) accum += v >> 32;
30 // Store lower half of result in limb pos in ret.
31 ret[3 - pos - i] = accum & 0xffffffff;
32 // Leave carry in accum.
33 accum >>= 32;
34 }
35 // Make sure no overflow.
36 assert(accum == 0);
37 };
38
39 // Multiply the 4 individual limbs (schoolbook multiply, with base 2^32).
40 add_fn((a & 0xffffffff) * (b & 0xffffffff), 0);
41 add_fn((a >> 32) * (b & 0xffffffff), 1);
42 add_fn((a & 0xffffffff) * (b >> 32), 1);
43 add_fn((a >> 32) * (b >> 32), 2);
44 return ret;
45 }
46
47 /* comparison helper for std::array */
48 std::strong_ordering compare_arrays(const std::array<uint32_t, 4>& a, const std::array<uint32_t, 4>& b) {
49 for (size_t i = 0; i < a.size(); ++i) {
50 if (a[i] != b[i]) return a[i] <=> b[i];
51 }
52 return std::strong_ordering::equal;
53 }
54
55 std::strong_ordering MulCompare(int64_t a1, int64_t a2, int64_t b1, int64_t b2)
56 {
57 // Compute and compare signs.
58 int sign_a = (a1 == 0 ? 0 : a1 < 0 ? -1 : 1) * (a2 == 0 ? 0 : a2 < 0 ? -1 : 1);
59 int sign_b = (b1 == 0 ? 0 : b1 < 0 ? -1 : 1) * (b2 == 0 ? 0 : b2 < 0 ? -1 : 1);
60 if (sign_a != sign_b) return sign_a <=> sign_b;
61
62 // Compute absolute values.
63 uint64_t abs_a1 = static_cast<uint64_t>(a1), abs_a2 = static_cast<uint64_t>(a2);
64 uint64_t abs_b1 = static_cast<uint64_t>(b1), abs_b2 = static_cast<uint64_t>(b2);
65 // Use (~x + 1) instead of the equivalent (-x) to silence the linter; mod 2^64 behavior is
66 // intentional here.
67 if (a1 < 0) abs_a1 = ~abs_a1 + 1;
68 if (a2 < 0) abs_a2 = ~abs_a2 + 1;
69 if (b1 < 0) abs_b1 = ~abs_b1 + 1;
70 if (b2 < 0) abs_b2 = ~abs_b2 + 1;
71
72 // Compute products of absolute values.
73 auto mul_abs_a = Mul128(abs_a1, abs_a2);
74 auto mul_abs_b = Mul128(abs_b1, abs_b2);
75 if (sign_a < 0) {
76 return compare_arrays(mul_abs_b, mul_abs_a);
77 } else {
78 return compare_arrays(mul_abs_a, mul_abs_b);
79 }
80 }
81
82 } // namespace
83
84 FUZZ_TARGET(feefrac)
85 {
86 FuzzedDataProvider provider(buffer.data(), buffer.size());
87
88 int64_t f1 = provider.ConsumeIntegral<int64_t>();
89 int32_t s1 = provider.ConsumeIntegral<int32_t>();
90 if (s1 == 0) f1 = 0;
91 FeeFrac fr1(f1, s1);
92 assert(fr1.IsEmpty() == (s1 == 0));
93
94 int64_t f2 = provider.ConsumeIntegral<int64_t>();
95 int32_t s2 = provider.ConsumeIntegral<int32_t>();
96 if (s2 == 0) f2 = 0;
97 FeeFrac fr2(f2, s2);
98 assert(fr2.IsEmpty() == (s2 == 0));
99
100 // Feerate comparisons
101 auto cmp_feerate = MulCompare(f1, s2, f2, s1);
102 assert(FeeRateCompare(fr1, fr2) == cmp_feerate);
103 assert((fr1 << fr2) == std::is_lt(cmp_feerate));
104 assert((fr1 >> fr2) == std::is_gt(cmp_feerate));
105
106 // Compare with manual invocation of FeeFrac::Mul.
107 auto cmp_mul = FeeFrac::Mul(f1, s2) <=> FeeFrac::Mul(f2, s1);
108 assert(cmp_mul == cmp_feerate);
109
110 // Same, but using FeeFrac::MulFallback.
111 auto cmp_fallback = FeeFrac::MulFallback(f1, s2) <=> FeeFrac::MulFallback(f2, s1);
112 assert(cmp_fallback == cmp_feerate);
113
114 // Total order comparisons
115 auto cmp_total = std::is_eq(cmp_feerate) ? (s2 <=> s1) : cmp_feerate;
116 assert((fr1 <=> fr2) == cmp_total);
117 assert((fr1 < fr2) == std::is_lt(cmp_total));
118 assert((fr1 > fr2) == std::is_gt(cmp_total));
119 assert((fr1 <= fr2) == std::is_lteq(cmp_total));
120 assert((fr1 >= fr2) == std::is_gteq(cmp_total));
121 assert((fr1 == fr2) == std::is_eq(cmp_total));
122 assert((fr1 != fr2) == std::is_neq(cmp_total));
123 }
124