fork of https://github.com/oxigraph/rocksdb and https://github.com/facebook/rocksdb for nextgraph and oxigraph
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
67 lines
2.5 KiB
67 lines
2.5 KiB
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
|
|
// This source code is licensed under the BSD-style license found in the
|
|
// LICENSE file in the root directory of this source tree. An additional grant
|
|
// of patent rights can be found in the PATENTS file in the same directory.
|
|
//
|
|
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
|
|
// Use of this source code is governed by a BSD-style license that can be
|
|
// found in the LICENSE file. See the AUTHORS file for names of contributors.
|
|
|
|
#include <string.h>
|
|
#include "util/coding.h"
|
|
#include "util/hash.h"
|
|
|
|
namespace rocksdb {
|
|
|
|
// This function may intentionally do a left shift on a -ve number
|
|
#if defined(__clang__)
|
|
__attribute__((__no_sanitize__("undefined")))
|
|
#elif __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 9)
|
|
__attribute__((__no_sanitize_undefined__))
|
|
#endif
|
|
uint32_t Hash(const char* data, size_t n, uint32_t seed) {
|
|
// Similar to murmur hash
|
|
const uint32_t m = 0xc6a4a793;
|
|
const uint32_t r = 24;
|
|
const char* limit = data + n;
|
|
uint32_t h = static_cast<uint32_t>(seed ^ (n * m));
|
|
|
|
// Pick up four bytes at a time
|
|
while (data + 4 <= limit) {
|
|
uint32_t w = DecodeFixed32(data);
|
|
data += 4;
|
|
h += w;
|
|
h *= m;
|
|
h ^= (h >> 16);
|
|
}
|
|
|
|
// Pick up remaining bytes
|
|
switch (limit - data) {
|
|
// Note: It would be better if this was cast to unsigned char, but that
|
|
// would be a disk format change since we previously didn't have any cast
|
|
// at all (so gcc used signed char).
|
|
// To understand the difference between shifting unsigned and signed chars,
|
|
// let's use 250 as an example. unsigned char will be 250, while signed char
|
|
// will be -6. Bit-wise, they are equivalent: 11111010. However, when
|
|
// converting negative number (signed char) to int, it will be converted
|
|
// into negative int (of equivalent value, which is -6), while converting
|
|
// positive number (unsigned char) will be converted to 250. Bitwise,
|
|
// this looks like this:
|
|
// signed char 11111010 -> int 11111111111111111111111111111010
|
|
// unsigned char 11111010 -> int 00000000000000000000000011111010
|
|
case 3:
|
|
h += static_cast<uint32_t>(static_cast<signed char>(data[2]) << 16);
|
|
// fall through
|
|
case 2:
|
|
h += static_cast<uint32_t>(static_cast<signed char>(data[1]) << 8);
|
|
// fall through
|
|
case 1:
|
|
h += static_cast<uint32_t>(static_cast<signed char>(data[0]));
|
|
h *= m;
|
|
h ^= (h >> r);
|
|
break;
|
|
}
|
|
return h;
|
|
}
|
|
|
|
} // namespace rocksdb
|
|
|