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turbonss/cxxmph/randomly_seeded_hash.h

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#ifndef __CXXMPH_RANDOMLY_SEEDED_HASH__
#define __CXXMPH_RANDOMLY_SEEDED_HASH__
// Helper to create randomly seeded hash functions out of existing hash
// functions that take a seed as a parameter.
#include <cstdlib>
#include "../src/cmph_types.h"
#include "MurmurHash2.h"
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#include "jenkins_hash.h"
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#include "stringpiece.h"
namespace cxxmph {
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template <class HashFun>
struct RandomlySeededHashFunction { };
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class JenkinsStringPiece { };
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class Murmur2StringPiece { };
class Murmur2Pod { };
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template <>
struct RandomlySeededHashFunction<JenkinsStringPiece> {
RandomlySeededHashFunction() {
srand(1);
seed = 4;
}
cmph_uint32 operator()(const StringPiece& key) const {
return jenkins_hash(key.data(), key.length(), seed);
}
void operator()(const StringPiece& key, cmph_uint32* hashes) const {
__jenkins_hash_vector(seed, key.data(), key.length(), hashes);
}
cmph_uint32 seed;
};
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template <>
struct RandomlySeededHashFunction<Murmur2StringPiece> {
RandomlySeededHashFunction() : seed(random()) { }
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cmph_uint32 operator()(const StringPiece& key) const {
return MurmurHash2(key.data(), key.length(), seed);
}
cmph_uint32 seed;
};
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template<>
struct RandomlySeededHashFunction<Murmur2Pod> {
RandomlySeededHashFunction() : seed(random()) { }
template<class Key>
cmph_uint32 operator()(const Key& key) const {
return MurmurHash2(&key, sizeof(key), seed);
}
cmph_uint32 seed;
};
} // namespace cxxmph
#endif // __CXXMPH_RANDOMLY_SEEDED_HASH__