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Merge bitcoin/bitcoin#23760: util: move MapIntoRange() for reuse in fuzz tests

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df2307cdc3 util: move MapIntoRange() for reuse in fuzz tests (fanquake)

Pull request description:

ACKs for top commit:
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    ACK df2307cdc3

Tree-SHA512: 31bf18f50a82e442ff025d6be0db5666b463a1fc16ec6b2112c77bb815515d27f8a537a0c9934c7daa3f4d526b47e8d6333f75a13b271e6efa550f8e71504b0a
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MarcoFalke 2022-01-06 14:54:06 +01:00
commit 70395bab4e
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3 changed files with 31 additions and 45 deletions
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31
src/blockfilter.cpp
View file

@ -24,37 +24,6 @@ static const std::map<BlockFilterType, std::string> g_filter_types = {
{BlockFilterType::BASIC, "basic"},
};
// 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 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
uint64_t x_hi = x >> 32;
uint64_t x_lo = x & 0xFFFFFFFF;
uint64_t n_hi = n >> 32;
uint64_t n_lo = n & 0xFFFFFFFF;
uint64_t ac = x_hi * n_hi;
uint64_t ad = x_hi * n_lo;
uint64_t bc = x_lo * n_hi;
uint64_t bd = x_lo * n_lo;
uint64_t mid34 = (bd >> 32) + (bc & 0xFFFFFFFF) + (ad & 0xFFFFFFFF);
uint64_t upper64 = ac + (bc >> 32) + (ad >> 32) + (mid34 >> 32);
return upper64;
#endif
}
uint64_t GCSFilter::HashToRange(const Element& element) const
{
uint64_t hash = CSipHasher(m_params.m_siphash_k0, m_params.m_siphash_k1)

14
src/test/fuzz/golomb_rice.cpp
View file

@ -19,20 +19,6 @@
#include <vector>
namespace {
uint64_t MapIntoRange(const uint64_t x, const uint64_t n)
{
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;
}
uint64_t HashToRange(const std::vector<uint8_t>& element, const uint64_t f)
{

31
src/util/golombrice.h
View file

@ -40,4 +40,35 @@ 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