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Add FastRange32 function and use it throughout the codebase

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This commit is contained in:
Pieter Wuille
2022-01-06 11:46:50 -05:00
parent 96ecd6fa3e
commit efab28b06b
3 changed files with 30 additions and 30 deletions
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13
src/common/bloom.cpp
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@@ -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;