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Correct computation of k hash functions.

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Matthias Vallentin 2013-06-06 14:54:25 -07:00
parent 289192623e
commit 0d299eca57
1 changed files with 1 additions and 8 deletions
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9
src/BloomFilter.cc
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@ -3,13 +3,6 @@
#include <cmath> #include <cmath>
#include "Serializer.h" #include "Serializer.h"
// Backport C++11's std::round().
namespace {
template <typename T>
T round(double x) { return (x > 0.0) ? (x + 0.5) : (x - 0.5); }
} // namespace <anonymous>
CounterVector::CounterVector(size_t width, size_t cells) CounterVector::CounterVector(size_t width, size_t cells)
: bits_(new BitVector(width * cells)), width_(width) : bits_(new BitVector(width * cells)), width_(width)
{ {
@ -155,7 +148,7 @@ size_t BasicBloomFilter::M(double fp, size_t capacity)
size_t BasicBloomFilter::K(size_t cells, size_t capacity) size_t BasicBloomFilter::K(size_t cells, size_t capacity)
{ {
double frac = static_cast<double>(cells) / static_cast<double>(capacity); double frac = static_cast<double>(cells) / static_cast<double>(capacity);
return round<size_t>(frac * std::log(2)); return std::ceil(frac * std::log(2));
} }
BasicBloomFilter::BasicBloomFilter(double fp, size_t capacity) BasicBloomFilter::BasicBloomFilter(double fp, size_t capacity)