watchman_hash.h

/* Copyright 2012-present Facebook, Inc.
 * Licensed under the Apache License, Version 2.0 */

#ifndef WATCHMAN_HASH_H
#define WATCHMAN_HASH_H

/* Bob Jenkins' lookup3.c hash function */
uint32_t w_hash_bytes(const void* key, size_t length, uint32_t initval);

namespace watchman {
// This is the Hash128to64 function from Google's cityhash (available
// under the MIT License).  We use it to reduce multiple 64 bit hashes
// into a single hash.
inline uint64_t hash_128_to_64(const uint64_t upper, const uint64_t lower) {
  // Murmur-inspired hashing.
  const uint64_t kMul = 0x9ddfea08eb382d69ULL;
  uint64_t a = (lower ^ upper) * kMul;
  a ^= (a >> 47);
  uint64_t b = (upper ^ a) * kMul;
  b ^= (b >> 47);
  b *= kMul;
  return b;
}
}

#endif

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