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// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
/*
* Ceph - scalable distributed file system
*
* Copyright (C) 2004-2006 Sage Weil <sage@newdream.net>
*
* This is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License version 2.1, as published by the Free Software
* Foundation. See file COPYING.
*
*/
#ifndef CEPH_BLOBHASH_H
#define CEPH_BLOBHASH_H
#include <cstdint>
#include "hash.h"
class blobhash {
public:
uint32_t operator()(const void* p, size_t len) {
static rjhash<std::uint32_t> H;
std::uint32_t acc = 0;
auto buf = static_cast<const unsigned char*>(p);
while (len >= sizeof(acc)) {
acc ^= unaligned_load(buf);
buf += sizeof(std::uint32_t);
len -= sizeof(std::uint32_t);
}
// handle the last few bytes of p[-(len % 4):]
switch (len) {
case 3:
acc ^= buf[2] << 16;
[[fallthrough]];
case 2:
acc ^= buf[1] << 8;
[[fallthrough]];
case 1:
acc ^= buf[0];
}
return H(acc);
}
private:
static inline std::uint32_t unaligned_load(const unsigned char* p) {
std::uint32_t result;
__builtin_memcpy(&result, p, sizeof(result));
return result;
}
};
#endif
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