Support SipHash with arbitrary byte writes

src/hash.h

@@ -171,19 +171,38 @@ unsigned int MurmurHash3(unsigned int nHashSeed, const std::vector<unsigned char
 
 void BIP32Hash(const ChainCode &chainCode, unsigned int nChild, unsigned char header, const unsigned char data[32], unsigned char output[64]);
 
-/** SipHash-2-4, using a uint64_t-based (rather than byte-based) interface */
+/** 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);
 
 #endif // BITCOIN_HASH_H