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// Copyright (c) 2016-present The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#ifndef BITCOIN_CRYPTO_SIPHASH_H
#define BITCOIN_CRYPTO_SIPHASH_H
#include <array>
#include <cstdint>
#include <span>
class uint256;
/** Shared SipHash internal state v[0..3], initialized from (k0, k1). */
class SipHashState
{
static constexpr uint64_t C0{0x736f6d6570736575ULL}, C1{0x646f72616e646f6dULL}, C2{0x6c7967656e657261ULL}, C3{0x7465646279746573ULL};
public:
explicit SipHashState(uint64_t k0, uint64_t k1) noexcept : v{C0 ^ k0, C1 ^ k1, C2 ^ k0, C3 ^ k1} {}
std::array<uint64_t, 4> v{};
};
/** General SipHash-2-4 implementation. */
class CSipHasher
{
SipHashState m_state;
uint64_t m_tmp{0};
uint8_t m_count{0}; //!< Only the low 8 bits of the input size matter.
public:
/** Construct a SipHash calculator initialized with 128-bit key (k0, k1). */
CSipHasher(uint64_t k0, uint64_t k1);
/** Hash a 64-bit integer worth of data.
* It is treated as if this was the little-endian interpretation of 8 bytes.
* This function can only be used when a multiple of 8 bytes have been written so far.
*/
CSipHasher& Write(uint64_t data);
/** Hash arbitrary bytes. */
CSipHasher& Write(std::span<const unsigned char> data);
/** Compute the 64-bit SipHash-2-4 of the data written so far. The object remains untouched. */
uint64_t Finalize() const;
};
/**
* Optimized SipHash-2-4 implementation for uint256.
*
* This class caches the initial SipHash v[0..3] state derived from (k0, k1)
* and implements a specialized hashing path for uint256 values, with or
* without an extra 32-bit word. The internal state is immutable, so
* PresaltedSipHasher instances can be reused for multiple hashes with the
* same key.
*/
class PresaltedSipHasher
{
const SipHashState m_state;
public:
explicit PresaltedSipHasher(uint64_t k0, uint64_t k1) noexcept : m_state{k0, k1} {}
/** Equivalent to CSipHasher(k0, k1).Write(val).Finalize(). */
uint64_t operator()(const uint256& val) const noexcept;
/**
* Equivalent to CSipHasher(k0, k1).Write(val).Write(extra).Finalize(),
* with `extra` encoded as 4 little-endian bytes.
*/
uint64_t operator()(const uint256& val, uint32_t extra) const noexcept;
};
#endif // BITCOIN_CRYPTO_SIPHASH_H