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authorMarcoFalke <falke.marco@gmail.com>2022-01-10 10:53:39 +0100
committerMarcoFalke <falke.marco@gmail.com>2022-01-10 10:53:45 +0100
commit3d0850cec103950731bfc0f935ad997a4149d4b3 (patch)
tree65eb7ff0124e24ad7c09e63789c32abbeca95cb1
parent542e405a8517e50bf6687a02af69117931234fde (diff)
parentefab28b06bfaa50c41337e84136cb58437e7ba00 (diff)
Merge bitcoin/bitcoin#23994: Consolidate all uses of the fast range mapping technique in util/fastrange.h
efab28b06bfaa50c41337e84136cb58437e7ba00 Add FastRange32 function and use it throughout the codebase (Pieter Wuille) 96ecd6fa3e0f53c3a25eb7c328220b819f8dde03 scripted-diff: rename MapIntoRange to FastRange64 (Pieter Wuille) c6d15c45d971fb25551b7a66a2615e3f0bee999b [moveonly] Move MapIntoRange() to separate util/fastrange.h (Pieter Wuille) Pull request description: Several places in the codebase use the fast range mapping technique described in https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction/, some for 32-bit ranges, some for 64-bit ones. Move all of these to `util/fastrange.h`, and give them a consistent name. ACKs for top commit: Sjors: ACK efab28b06bfaa50c41337e84136cb58437e7ba00 shaavan: reACK efab28b06bfaa50c41337e84136cb58437e7ba00 MarcoFalke: review ACK efab28b06bfaa50c41337e84136cb58437e7ba00 🍸 Tree-SHA512: 3190a25ef21d17f0ab2afcd9b8d5a1813fdfac0d93996878017e84ff62eee412c823d6149ae8e92cfc3214458641e83ace4b022b4a0fe0679f78dbaee21c6227
Diffstat
-rw-r--r--src/Makefile.am1
-rw-r--r--src/blockfilter.cpp2
-rw-r--r--src/common/bloom.cpp13
-rw-r--r--src/cuckoocache.h27
-rw-r--r--src/test/fuzz/golomb_rice.cpp2
-rw-r--r--src/util/fastrange.h51
-rw-r--r--src/util/golombrice.h33
7 files changed, 71 insertions, 58 deletions
diff --git a/src/Makefile.am b/src/Makefile.am
index b946a325c9..0b177480c8 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -240,6 +240,7 @@ BITCOIN_CORE_H = \
util/check.h \
util/epochguard.h \
util/error.h \
+ util/fastrange.h \
util/fees.h \
util/getuniquepath.h \
util/golombrice.h \
diff --git a/src/blockfilter.cpp b/src/blockfilter.cpp
index 566254d839..63a9ba498f 100644
--- a/src/blockfilter.cpp
+++ b/src/blockfilter.cpp
@@ -29,7 +29,7 @@ uint64_t GCSFilter::HashToRange(const Element& element) const
uint64_t hash = CSipHasher(m_params.m_siphash_k0, m_params.m_siphash_k1)
.Write(element.data(), element.size())
.Finalize();
- return MapIntoRange(hash, m_F);
+ return FastRange64(hash, m_F);
}
std::vector<uint64_t> GCSFilter::BuildHashedSet(const ElementSet& elements) const
diff --git a/src/common/bloom.cpp b/src/common/bloom.cpp
index c3603b5d2a..0bb72dbcbb 100644
--- a/src/common/bloom.cpp
+++ b/src/common/bloom.cpp
@@ -11,6 +11,7 @@
#include <script/standard.h>
#include <span.h>
#include <streams.h>
+#include <util/fastrange.h>
#include <algorithm>
#include <cmath>
@@ -191,14 +192,6 @@ static inline uint32_t RollingBloomHash(unsigned int nHashNum, uint32_t nTweak,
return MurmurHash3(nHashNum * 0xFBA4C795 + nTweak, vDataToHash);
}
-
-// A replacement for x % n. This assumes that x and n are 32bit integers, and x is a uniformly random distributed 32bit value
-// which should be the case for a good hash.
-// See https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction/
-static inline uint32_t FastMod(uint32_t x, size_t n) {
- return ((uint64_t)x * (uint64_t)n) >> 32;
-}
-
void CRollingBloomFilter::insert(Span<const unsigned char> vKey)
{
if (nEntriesThisGeneration == nEntriesPerGeneration) {
@@ -223,7 +216,7 @@ void CRollingBloomFilter::insert(Span<const unsigned char> vKey)
uint32_t h = RollingBloomHash(n, nTweak, vKey);
int bit = h & 0x3F;
/* FastMod works with the upper bits of h, so it is safe to ignore that the lower bits of h are already used for bit. */
- uint32_t pos = FastMod(h, data.size());
+ uint32_t pos = FastRange32(h, data.size());
/* The lowest bit of pos is ignored, and set to zero for the first bit, and to one for the second. */
data[pos & ~1] = (data[pos & ~1] & ~(((uint64_t)1) << bit)) | ((uint64_t)(nGeneration & 1)) << bit;
data[pos | 1] = (data[pos | 1] & ~(((uint64_t)1) << bit)) | ((uint64_t)(nGeneration >> 1)) << bit;
@@ -235,7 +228,7 @@ bool CRollingBloomFilter::contains(Span<const unsigned char> vKey) const
for (int n = 0; n < nHashFuncs; n++) {
uint32_t h = RollingBloomHash(n, nTweak, vKey);
int bit = h & 0x3F;
- uint32_t pos = FastMod(h, data.size());
+ uint32_t pos = FastRange32(h, data.size());
/* If the relevant bit is not set in either data[pos & ~1] or data[pos | 1], the filter does not contain vKey */
if (!(((data[pos & ~1] | data[pos | 1]) >> bit) & 1)) {
return false;
diff --git a/src/cuckoocache.h b/src/cuckoocache.h
index 15cb55c3ce..d0dc61c7e6 100644
--- a/src/cuckoocache.h
+++ b/src/cuckoocache.h
@@ -5,6 +5,8 @@
#ifndef BITCOIN_CUCKOOCACHE_H
#define BITCOIN_CUCKOOCACHE_H
+#include <util/fastrange.h>
+
#include <algorithm> // std::find
#include <array>
#include <atomic>
@@ -219,13 +221,8 @@ private:
* One option would be to implement the same trick the compiler uses and compute the
* constants for exact division based on the size, as described in "{N}-bit Unsigned
* Division via {N}-bit Multiply-Add" by Arch D. Robison in 2005. But that code is
- * somewhat complicated and the result is still slower than other options:
- *
- * Instead we treat the 32-bit random number as a Q32 fixed-point number in the range
- * [0, 1) and simply multiply it by the size. Then we just shift the result down by
- * 32-bits to get our bucket number. The result has non-uniformity the same as a
- * mod, but it is much faster to compute. More about this technique can be found at
- * https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction/ .
+ * somewhat complicated and the result is still slower than an even simpler option:
+ * see the FastRange32 function in util/fastrange.h.
*
* The resulting non-uniformity is also more equally distributed which would be
* advantageous for something like linear probing, though it shouldn't matter
@@ -241,14 +238,14 @@ private:
*/
inline std::array<uint32_t, 8> compute_hashes(const Element& e) const
{
- return {{(uint32_t)(((uint64_t)hash_function.template operator()<0>(e) * (uint64_t)size) >> 32),
- (uint32_t)(((uint64_t)hash_function.template operator()<1>(e) * (uint64_t)size) >> 32),
- (uint32_t)(((uint64_t)hash_function.template operator()<2>(e) * (uint64_t)size) >> 32),
- (uint32_t)(((uint64_t)hash_function.template operator()<3>(e) * (uint64_t)size) >> 32),
- (uint32_t)(((uint64_t)hash_function.template operator()<4>(e) * (uint64_t)size) >> 32),
- (uint32_t)(((uint64_t)hash_function.template operator()<5>(e) * (uint64_t)size) >> 32),
- (uint32_t)(((uint64_t)hash_function.template operator()<6>(e) * (uint64_t)size) >> 32),
- (uint32_t)(((uint64_t)hash_function.template operator()<7>(e) * (uint64_t)size) >> 32)}};
+ return {{FastRange32(hash_function.template operator()<0>(e), size),
+ FastRange32(hash_function.template operator()<1>(e), size),
+ FastRange32(hash_function.template operator()<2>(e), size),
+ FastRange32(hash_function.template operator()<3>(e), size),
+ FastRange32(hash_function.template operator()<4>(e), size),
+ FastRange32(hash_function.template operator()<5>(e), size),
+ FastRange32(hash_function.template operator()<6>(e), size),
+ FastRange32(hash_function.template operator()<7>(e), size)}};
}
/** invalid returns a special index that can never be inserted to
diff --git a/src/test/fuzz/golomb_rice.cpp b/src/test/fuzz/golomb_rice.cpp
index 2d0b29953c..b4bb4c6dc6 100644
--- a/src/test/fuzz/golomb_rice.cpp
+++ b/src/test/fuzz/golomb_rice.cpp
@@ -25,7 +25,7 @@ uint64_t HashToRange(const std::vector<uint8_t>& element, const uint64_t f)
const uint64_t hash = CSipHasher(0x0706050403020100ULL, 0x0F0E0D0C0B0A0908ULL)
.Write(element.data(), element.size())
.Finalize();
- return MapIntoRange(hash, f);
+ return FastRange64(hash, f);
}
std::vector<uint64_t> BuildHashedSet(const std::unordered_set<std::vector<uint8_t>, ByteVectorHash>& elements, const uint64_t f)
diff --git a/src/util/fastrange.h b/src/util/fastrange.h
new file mode 100644
index 0000000000..77cb883ce0
--- /dev/null
+++ b/src/util/fastrange.h
@@ -0,0 +1,51 @@
+// Copyright (c) 2018-2020 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_FASTRANGE_H
+#define BITCOIN_UTIL_FASTRANGE_H
+
+#include <cstdint>
+
+/* This file offers implementations of the fast range reduction technique described
+ * in https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction/
+ *
+ * In short, they take an integer x and a range n, and return the upper bits of
+ * (x * n). If x is uniformly distributed over its domain, the result is as close to
+ * uniformly distributed over [0, n) as (x mod n) would be, but significantly faster.
+ */
+
+/** Fast range reduction with 32-bit input and 32-bit range. */
+static inline uint32_t FastRange32(uint32_t x, uint32_t n)
+{
+ return (uint64_t{x} * n) >> 32;
+}
+
+/** Fast range reduction with 64-bit input and 64-bit range. */
+static inline uint64_t FastRange64(uint64_t x, uint64_t n)
+{
+#ifdef __SIZEOF_INT128__
+ return (static_cast<unsigned __int128>(x) * static_cast<unsigned __int128>(n)) >> 64;
+#else
+ // To perform the calculation on 64-bit numbers without losing the
+ // result to overflow, split the numbers into the most significant and
+ // least significant 32 bits and perform multiplication piece-wise.
+ //
+ // See: https://stackoverflow.com/a/26855440
+ const uint64_t x_hi = x >> 32;
+ const uint64_t x_lo = x & 0xFFFFFFFF;
+ const uint64_t n_hi = n >> 32;
+ const uint64_t n_lo = n & 0xFFFFFFFF;
+
+ const uint64_t ac = x_hi * n_hi;
+ const uint64_t ad = x_hi * n_lo;
+ const uint64_t bc = x_lo * n_hi;
+ const uint64_t bd = x_lo * n_lo;
+
+ const uint64_t mid34 = (bd >> 32) + (bc & 0xFFFFFFFF) + (ad & 0xFFFFFFFF);
+ const uint64_t upper64 = ac + (bc >> 32) + (ad >> 32) + (mid34 >> 32);
+ return upper64;
+#endif
+}
+
+#endif // BITCOIN_UTIL_FASTRANGE_H
diff --git a/src/util/golombrice.h b/src/util/golombrice.h
index f14cb594db..4ff4f6d7e5 100644
--- a/src/util/golombrice.h
+++ b/src/util/golombrice.h
@@ -5,6 +5,8 @@
#ifndef BITCOIN_UTIL_GOLOMBRICE_H
#define BITCOIN_UTIL_GOLOMBRICE_H
+#include <util/fastrange.h>
+
#include <streams.h>
#include <cstdint>
@@ -40,35 +42,4 @@ uint64_t GolombRiceDecode(BitStreamReader<IStream>& bitreader, uint8_t P)
return (q << P) + r;
}
-// Map a value x that is uniformly distributed in the range [0, 2^64) to a
-// value uniformly distributed in [0, n) by returning the upper 64 bits of
-// x * n.
-//
-// See: https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction/
-static inline uint64_t MapIntoRange(uint64_t x, uint64_t n)
-{
-#ifdef __SIZEOF_INT128__
- return (static_cast<unsigned __int128>(x) * static_cast<unsigned __int128>(n)) >> 64;
-#else
- // To perform the calculation on 64-bit numbers without losing the
- // result to overflow, split the numbers into the most significant and
- // least significant 32 bits and perform multiplication piece-wise.
- //
- // See: https://stackoverflow.com/a/26855440
- const uint64_t x_hi = x >> 32;
- const uint64_t x_lo = x & 0xFFFFFFFF;
- const uint64_t n_hi = n >> 32;
- const uint64_t n_lo = n & 0xFFFFFFFF;
-
- const uint64_t ac = x_hi * n_hi;
- const uint64_t ad = x_hi * n_lo;
- const uint64_t bc = x_lo * n_hi;
- const uint64_t bd = x_lo * n_lo;
-
- const uint64_t mid34 = (bd >> 32) + (bc & 0xFFFFFFFF) + (ad & 0xFFFFFFFF);
- const uint64_t upper64 = ac + (bc >> 32) + (ad >> 32) + (mid34 >> 32);
- return upper64;
-#endif
-}
-
#endif // BITCOIN_UTIL_GOLOMBRICE_H
generated by cgit v1.2.3 (git 2.26.2) at 2025-03-17 06:29:37 +0000