Repository: bitcoin/bitcoin
File: src/crypto/siphash.h (C/C++)

Code before:
// 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 <cstdint>
#include <span>

class uint256;

/** SipHash-2-4 */
class CSipHasher
{
private:
    uint64_t v[4];
    uint64_t tmp;
    uint8_t count; // 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.
 *
 *  It is identical to:
 *    SipHasher(k0, k1)
 *      .Write(val.GetUint64(0))
 *      .Write(val.GetUint64(1))
 *      .Write(val.GetUint64(2))
 *      .Write(val.GetUint64(3))
 *      .Finalize()
 */
uint64_t SipHashUint256(uint64_t k0, uint64_t k1, const uint256& val);
uint64_t SipHashUint256Extra(uint64_t k0, uint64_t k1, const uint256& val, uint32_t extra);

#endif // BITCOIN_CRYPTO_SIPHASH_H


Review comment (refactor):
In commit "refactor: extract shared SipHash state into SipSalt"

These could be doxygen comments (`/** Equivalent to ... */`).

Code after:
    /** 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