Branch data Line data Source code
1 : : // Copyright (c) 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 : : #ifndef BITCOIN_UTIL_FEEFRAC_H
6 : : #define BITCOIN_UTIL_FEEFRAC_H
7 : :
8 : : #include <stdint.h>
9 : : #include <compare>
10 : : #include <vector>
11 : : #include <span.h>
12 : : #include <util/check.h>
13 : :
14 : : /** Data structure storing a fee and size, ordered by increasing fee/size.
15 : : *
16 : : * The size of a FeeFrac cannot be zero unless the fee is also zero.
17 : : *
18 : : * FeeFracs have a total ordering, first by increasing feerate (ratio of fee over size), and then
19 : : * by decreasing size. The empty FeeFrac (fee and size both 0) sorts last. So for example, the
20 : : * following FeeFracs are in sorted order:
21 : : *
22 : : * - fee=0 size=1 (feerate 0)
23 : : * - fee=1 size=2 (feerate 0.5)
24 : : * - fee=2 size=3 (feerate 0.667...)
25 : : * - fee=2 size=2 (feerate 1)
26 : : * - fee=1 size=1 (feerate 1)
27 : : * - fee=3 size=2 (feerate 1.5)
28 : : * - fee=2 size=1 (feerate 2)
29 : : * - fee=0 size=0 (undefined feerate)
30 : : *
31 : : * A FeeFrac is considered "better" if it sorts after another, by this ordering. All standard
32 : : * comparison operators (<=>, ==, !=, >, <, >=, <=) respect this ordering.
33 : : *
34 : : * The FeeRateCompare, and >> and << operators only compare feerate and treat equal feerate but
35 : : * different size as equivalent. The empty FeeFrac is neither lower or higher in feerate than any
36 : : * other.
37 : : */
38 : : struct FeeFrac
39 : : {
40 : : /** Helper function for 32*64 signed multiplication, returning an unspecified but totally
41 : : * ordered type. This is a fallback version, separate so it can be tested on platforms where
42 : : * it isn't actually needed. */
43 : : static inline std::pair<int64_t, uint32_t> MulFallback(int64_t a, int32_t b) noexcept
44 : : {
45 : : int64_t low = int64_t{static_cast<uint32_t>(a)} * b;
46 : : int64_t high = (a >> 32) * b;
47 : : return {high + (low >> 32), static_cast<uint32_t>(low)};
48 : : }
49 : :
50 : : /** Helper function for 96/32 signed division, rounding towards negative infinity (if
51 : : * round_down) or positive infinity (if !round_down). This is a fallback version, separate so
52 : : * that it can be tested on platforms where it isn't actually needed.
53 : : *
54 : : * The exact behavior with negative n does not really matter, but this implementation chooses
55 : : * to be consistent for testability reasons.
56 : : *
57 : : * The result must fit in an int64_t, and d must be strictly positive. */
58 : : static inline int64_t DivFallback(std::pair<int64_t, uint32_t> n, int32_t d, bool round_down) noexcept
59 : : {
60 : : Assume(d > 0);
61 : : // Compute quot_high = n.first / d, so the result becomes
62 : : // (n.second + (n.first - quot_high * d) * 2**32) / d + (quot_high * 2**32), or
63 : : // (n.second + (n.first % d) * 2**32) / d + (quot_high * 2**32).
64 : : int64_t quot_high = n.first / d;
65 : : // Evaluate the parenthesized expression above, so the result becomes
66 : : // n_low / d + (quot_high * 2**32)
67 : : int64_t n_low = ((n.first % d) << 32) + n.second;
68 : : // Evaluate the division so the result becomes quot_low + quot_high * 2**32. It is possible
69 : : // that the / operator here rounds in the wrong direction (if n_low is not a multiple of
70 : : // size, and is (if round_down) negative, or (if !round_down) positive). If so, make a
71 : : // correction.
72 : : int64_t quot_low = n_low / d;
73 : : int32_t mod_low = n_low % d;
74 : : quot_low += (mod_low > 0) - (mod_low && round_down);
75 : : // Combine and return the result
76 : : return (quot_high << 32) + quot_low;
77 : : }
78 : :
79 : : #ifdef __SIZEOF_INT128__
80 : : /** Helper function for 32*64 signed multiplication, returning an unspecified but totally
81 : : * ordered type. This is a version relying on __int128. */
82 : 42432673 : static inline __int128 Mul(int64_t a, int32_t b) noexcept
83 : : {
84 : 42432675 : return __int128{a} * b;
85 : : }
86 : :
87 : : /** Helper function for 96/32 signed division, rounding towards negative infinity (if
88 : : * round_down), or towards positive infinity (if !round_down). This is a
89 : : * version relying on __int128.
90 : : *
91 : : * The result must fit in an int64_t, and d must be strictly positive. */
92 : 42 : static inline int64_t Div(__int128 n, int32_t d, bool round_down) noexcept
93 : : {
94 : 42 : Assume(d > 0);
95 : : // Compute the division.
96 : 42 : int64_t quot = n / d;
97 : 42 : int32_t mod = n % d;
98 : : // Correct result if the / operator above rounded in the wrong direction.
99 : 42 : return quot + (mod > 0) - (mod && round_down);
100 : : }
101 : : #else
102 : : static constexpr auto Mul = MulFallback;
103 : : static constexpr auto Div = DivFallback;
104 : : #endif
105 : :
106 : : int64_t fee;
107 : : int32_t size;
108 : :
109 : : /** Construct an IsEmpty() FeeFrac. */
110 : 30 : constexpr inline FeeFrac() noexcept : fee{0}, size{0} {}
111 : :
112 : : /** Construct a FeeFrac with specified fee and size. */
113 [ + + + + ]: 39038749 : constexpr inline FeeFrac(int64_t f, int32_t s) noexcept : fee{f}, size{s} {}
[ + + ][ + -
+ - + - +
- + - + -
+ - + - +
- + - ]
114 : :
115 : : constexpr inline FeeFrac(const FeeFrac&) noexcept = default;
116 : : constexpr inline FeeFrac& operator=(const FeeFrac&) noexcept = default;
117 : :
118 : : /** Check if this is empty (size and fee are 0). */
119 : 20 : bool inline IsEmpty() const noexcept {
120 [ + - # # : 20 : return size == 0;
# # # # ]
[ # # ]
121 : : }
122 : :
123 : : /** Add fee and size of another FeeFrac to this one. */
124 : 276 : void inline operator+=(const FeeFrac& other) noexcept
125 : : {
126 : 276 : fee += other.fee;
127 [ # # # # : 276 : size += other.size;
# # # # ]
128 : : }
129 : :
130 : : /** Subtract fee and size of another FeeFrac from this one. */
131 : 0 : void inline operator-=(const FeeFrac& other) noexcept
132 : : {
133 : 0 : fee -= other.fee;
134 [ # # ]: 0 : size -= other.size;
135 : : }
136 : :
137 : : /** Sum fee and size. */
138 : 452 : friend inline FeeFrac operator+(const FeeFrac& a, const FeeFrac& b) noexcept
139 : : {
140 : 452 : return {a.fee + b.fee, a.size + b.size};
141 : : }
142 : :
143 : : /** Subtract both fee and size. */
144 : 338 : friend inline FeeFrac operator-(const FeeFrac& a, const FeeFrac& b) noexcept
145 : : {
146 [ + - ]: 249 : return {a.fee - b.fee, a.size - b.size};
[ + + + + ]
147 : : }
148 : :
149 : : /** Check if two FeeFrac objects are equal (both same fee and same size). */
150 : 19514731 : friend inline bool operator==(const FeeFrac& a, const FeeFrac& b) noexcept
151 : : {
152 [ + + + + ]: 19514731 : return a.fee == b.fee && a.size == b.size;
[ + - + +
+ + + + ]
[ + - - +
+ - - + +
- - + - +
- - - + -
- + - - +
+ - - + -
+ - - ]
153 : : }
154 : :
155 : : /** Compare two FeeFracs just by feerate. */
156 : 189 : friend inline std::weak_ordering FeeRateCompare(const FeeFrac& a, const FeeFrac& b) noexcept
157 : : {
158 : 189 : auto cross_a = Mul(a.fee, b.size), cross_b = Mul(b.fee, a.size);
159 [ + + + + ]: 189 : return cross_a <=> cross_b;
160 : : }
161 : :
162 : : /** Check if a FeeFrac object has strictly lower feerate than another. */
163 : 4 : friend inline bool operator<<(const FeeFrac& a, const FeeFrac& b) noexcept
164 : : {
165 [ + - ]: 1 : auto cross_a = Mul(a.fee, b.size), cross_b = Mul(b.fee, a.size);
166 [ + - + - : 4 : return cross_a < cross_b;
+ - + - ]
[ # # # #
# # # # ]
167 : : }
168 : :
169 : : /** Check if a FeeFrac object has strictly higher feerate than another. */
170 : 69 : friend inline bool operator>>(const FeeFrac& a, const FeeFrac& b) noexcept
171 : : {
172 [ + - ]: 67 : auto cross_a = Mul(a.fee, b.size), cross_b = Mul(b.fee, a.size);
173 [ + + ][ + - : 69 : return cross_a > cross_b;
+ - + - #
# # # ][ #
# # # #
# ]
174 : : }
175 : :
176 : : /** Compare two FeeFracs. <, >, <=, and >= are auto-generated from this. */
177 : 42432369 : friend inline std::strong_ordering operator<=>(const FeeFrac& a, const FeeFrac& b) noexcept
178 : : {
179 : 42432369 : auto cross_a = Mul(a.fee, b.size), cross_b = Mul(b.fee, a.size);
180 [ + + + + : 42432369 : if (cross_a == cross_b) return b.size <=> a.size;
+ + ]
181 [ + + ]: 560779 : return cross_a <=> cross_b;
182 : : }
183 : :
184 : : /** Swap two FeeFracs. */
185 : 145 : friend inline void swap(FeeFrac& a, FeeFrac& b) noexcept
186 : : {
187 : 7 : std::swap(a.fee, b.fee);
188 : 7 : std::swap(a.size, b.size);
189 : : }
190 : :
191 : : /** Compute the fee for a given size `at_size` using this object's feerate.
192 : : *
193 : : * This effectively corresponds to evaluating (this->fee * at_size) / this->size, with the
194 : : * result rounded towards negative infinity (if RoundDown) or towards positive infinity
195 : : * (if !RoundDown).
196 : : *
197 : : * Requires this->size > 0, at_size >= 0, and that the correct result fits in a int64_t. This
198 : : * is guaranteed to be the case when 0 <= at_size <= this->size.
199 : : */
200 : : template<bool RoundDown>
201 : 60 : int64_t EvaluateFee(int32_t at_size) const noexcept
202 : : {
203 : : Assume(size > 0);
204 : : Assume(at_size >= 0);
205 [ + + ]: 60 : if (fee >= 0 && fee < 0x200000000) [[likely]] {
206 : : // Common case where (this->fee * at_size) is guaranteed to fit in a uint64_t.
207 : : if constexpr (RoundDown) {
208 : 9 : return (uint64_t(fee) * at_size) / uint32_t(size);
209 : : } else {
210 : 9 : return (uint64_t(fee) * at_size + size - 1U) / uint32_t(size);
211 : : }
212 : : } else {
213 : : // Otherwise, use Mul and Div.
214 : 42 : return Div(Mul(fee, at_size), size, RoundDown);
215 : : }
216 : : }
217 : :
218 : : public:
219 : : /** Compute the fee for a given size `at_size` using this object's feerate, rounding down. */
220 [ + - + - : 30 : int64_t EvaluateFeeDown(int32_t at_size) const noexcept { return EvaluateFee<true>(at_size); }
+ - + - +
- + - + -
+ - + - +
- + - + -
+ - + - +
- + - + -
+ - + - +
- + - + -
+ - + - +
- + - + -
+ - + - +
- ]
221 : : /** Compute the fee for a given size `at_size` using this object's feerate, rounding up. */
222 [ + - + - : 30 : int64_t EvaluateFeeUp(int32_t at_size) const noexcept { return EvaluateFee<false>(at_size); }
+ - + - +
- + - + -
+ - + - +
- + - + -
+ - + - +
- + - + -
+ - + - +
- + - + -
+ - + - +
- + - + -
+ - + - +
- ]
223 : : };
224 : :
225 : : /** Compare the feerate diagrams implied by the provided sorted chunks data.
226 : : *
227 : : * The implied diagram for each starts at (0, 0), then contains for each chunk the cumulative fee
228 : : * and size up to that chunk, and then extends infinitely to the right with a horizontal line.
229 : : *
230 : : * The caller must guarantee that the sum of the FeeFracs in either of the chunks' data set do not
231 : : * overflow (so sum fees < 2^63, and sum sizes < 2^31).
232 : : */
233 : : std::partial_ordering CompareChunks(std::span<const FeeFrac> chunks0, std::span<const FeeFrac> chunks1);
234 : :
235 : : /** Tagged wrapper around FeeFrac to avoid unit confusion. */
236 : : template<typename Tag>
237 : 0 : struct FeePerUnit : public FeeFrac
238 : : {
239 : : // Inherit FeeFrac constructors.
240 : 0 : using FeeFrac::FeeFrac;
241 : :
242 : : /** Convert a FeeFrac to a FeePerUnit. */
243 : 0 : static FeePerUnit FromFeeFrac(const FeeFrac& feefrac) noexcept
244 : : {
245 [ # # ]: 0 : return {feefrac.fee, feefrac.size};
246 : : }
247 : : };
248 : :
249 : : // FeePerUnit instance for satoshi / vbyte.
250 : : struct VSizeTag {};
251 : : using FeePerVSize = FeePerUnit<VSizeTag>;
252 : :
253 : : // FeePerUnit instance for satoshi / WU.
254 : : struct WeightTag {};
255 : : using FeePerWeight = FeePerUnit<WeightTag>;
256 : :
257 : : #endif // BITCOIN_UTIL_FEEFRAC_H
|
