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/*
* Copyright 2017 The Native Object Protocols Authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef LIBNOP_INCLUDE_NOP_UTILITY_SIP_HASH_H_
#define LIBNOP_INCLUDE_NOP_UTILITY_SIP_HASH_H_
#include <array>
#include <cstdint>
#include <nop/utility/compiler.h>
// A direct port of the SipHash C reference implementation.
//
// https://131002.net/siphash/siphash24.c
//
// This version supports compile-time constexpr hash computation when provided
// with a byte container that supports constexpr size() and operator[] methods.
//
namespace nop {
// A simple byte container/wrapper with constexpr size() and operator[] methods.
template <typename T>
class BlockReader {
public:
static_assert(sizeof(T) == 1, "sizeof(T) != 1");
using ValueType = T;
template <std::size_t Size>
constexpr BlockReader(const ValueType (&value)[Size])
: data_{value}, size_{Size} {}
constexpr BlockReader(const ValueType* data, std::size_t size)
: data_{data}, size_{size} {}
BlockReader(const BlockReader&) = default;
BlockReader& operator=(const BlockReader&) = default;
constexpr std::size_t size() const { return size_; }
constexpr ValueType operator[](const std::size_t index) const {
return data_[index];
}
private:
const ValueType* data_;
std::size_t size_;
};
// Captures a hash value as a compile-time type.
template <std::uint64_t Hash_>
struct HashValue {
enum : std::uint64_t { Value = Hash_ };
};
struct SipHash {
template <typename T, std::size_t Size>
static constexpr std::uint64_t Compute(const T (&buffer)[Size],
std::uint64_t k0, std::uint64_t k1) {
return Compute(BlockReader<T>(buffer), k0, k1);
}
template <typename BufferType>
static constexpr std::uint64_t Compute(const BufferType buffer,
std::uint64_t k0, std::uint64_t k1) {
const std::size_t kBlockSize = sizeof(std::uint64_t);
const std::size_t kLength = buffer.size();
const std::size_t kLeftOver = kLength % kBlockSize;
const std::size_t kEndOffset = kLength - kLeftOver;
std::uint64_t v[4] = {0x736f6d6570736575ULL, 0x646f72616e646f6dULL,
0x6c7967656e657261ULL, 0x7465646279746573ULL};
std::uint64_t b = static_cast<std::uint64_t>(kLength) << 56;
v[3] ^= k1;
v[2] ^= k0;
v[1] ^= k1;
v[0] ^= k0;
for (std::size_t offset = 0; offset < kEndOffset; offset += kBlockSize) {
std::uint64_t m = ReadBlock(buffer, offset);
v[3] ^= m;
Round(v);
Round(v);
v[0] ^= m;
}
switch (kLeftOver) {
case 7:
b |= static_cast<std::uint64_t>(buffer[kEndOffset + 6]) << 48;
NOP_FALLTHROUGH;
case 6:
b |= static_cast<std::uint64_t>(buffer[kEndOffset + 5]) << 40;
NOP_FALLTHROUGH;
case 5:
b |= static_cast<std::uint64_t>(buffer[kEndOffset + 4]) << 32;
NOP_FALLTHROUGH;
case 4:
b |= static_cast<std::uint64_t>(buffer[kEndOffset + 3]) << 24;
NOP_FALLTHROUGH;
case 3:
b |= static_cast<std::uint64_t>(buffer[kEndOffset + 2]) << 16;
NOP_FALLTHROUGH;
case 2:
b |= static_cast<std::uint64_t>(buffer[kEndOffset + 1]) << 8;
NOP_FALLTHROUGH;
case 1:
b |= static_cast<std::uint64_t>(buffer[kEndOffset + 0]) << 0;
NOP_FALLTHROUGH;
case 0:
break;
}
v[3] ^= b;
Round(v);
Round(v);
v[0] ^= b;
v[2] ^= 0xff;
Round(v);
Round(v);
Round(v);
Round(v);
b = v[0] ^ v[1] ^ v[2] ^ v[3];
return b;
}
private:
template <typename BufferType>
static constexpr std::uint64_t ReadBlock(const BufferType buffer,
const std::size_t offset) {
const std::uint64_t v0 = buffer[offset + 0];
const std::uint64_t v1 = buffer[offset + 1];
const std::uint64_t v2 = buffer[offset + 2];
const std::uint64_t v3 = buffer[offset + 3];
const std::uint64_t v4 = buffer[offset + 4];
const std::uint64_t v5 = buffer[offset + 5];
const std::uint64_t v6 = buffer[offset + 6];
const std::uint64_t v7 = buffer[offset + 7];
return ((v7 << 56) | (v6 << 48) | (v5 << 40) | (v4 << 32) | (v3 << 24) |
(v2 << 16) | (v1 << 8) | (v0 << 0));
}
static constexpr std::uint64_t RotateLeft(const std::uint64_t x,
const std::uint64_t b) {
return (x << b) | (x >> (64 - b));
}
static constexpr void Round(std::uint64_t (&v)[4]) {
v[0] += v[1];
v[1] = RotateLeft(v[1], 13);
v[1] ^= v[0];
v[0] = RotateLeft(v[0], 32);
v[2] += v[3];
v[3] = RotateLeft(v[3], 16);
v[3] ^= v[2];
v[0] += v[3];
v[3] = RotateLeft(v[3], 21);
v[3] ^= v[0];
v[2] += v[1];
v[1] = RotateLeft(v[1], 17);
v[1] ^= v[2];
v[2] = RotateLeft(v[2], 32);
}
};
} // namespace nop
#endif // LIBNOP_INCLUDE_NOP_UTILITY_SIP_HASH_H_
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