Extract CSipHasher to it's own file in crypto/ directory.

This is a move-only commit with the exception of changes to includes.

src/crypto/siphash.h

@@ -0,0 +1,47 @@
+// Copyright (c) 2016-2018 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 <stdint.h>
+
+#include <uint256.h>
+
+/** SipHash-2-4 */
+class CSipHasher
+{
+private:
+    uint64_t v[4];
+    uint64_t tmp;
+    int count;
+
+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(const unsigned char* data, size_t size);
+    /** 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