change the mechanism for "internal" buffer storage

[folly.git] / folly / SpookyHash.h

/*
 * Copyright 2012 Facebook, Inc.
 *
 * 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.
 */

//
// SpookyHash: a 128-bit noncryptographic hash function
// By Bob Jenkins, public domain
//   Oct 31 2010: alpha, framework + SpookyHash::Mix appears right
//   Oct 31 2011: alpha again, Mix only good to 2^^69 but rest appears right
//   Dec 31 2011: beta, improved Mix, tested it for 2-bit deltas
//   Feb  2 2012: production, same bits as beta
//   Feb  5 2012: adjusted definitions of uint* to be more portable
//   Mar 30 2012: 3 bytes/cycle, not 4.  Alpha was 4 but wasn't thorough enough.
//
// Up to 3 bytes/cycle for long messages.  Reasonably fast for short messages.
// All 1 or 2 bit deltas achieve avalanche within 1% bias per output bit.
//
// This was developed for and tested on 64-bit x86-compatible processors.
// It assumes the processor is little-endian.  There is a macro
// controlling whether unaligned reads are allowed (by default they are).
// This should be an equally good hash on big-endian machines, but it will
// compute different results on them than on little-endian machines.
//
// Google's CityHash has similar specs to SpookyHash, and CityHash is faster
// on some platforms.  MD4 and MD5 also have similar specs, but they are orders
// of magnitude slower.  CRCs are two or more times slower, but unlike
// SpookyHash, they have nice math for combining the CRCs of pieces to form
// the CRCs of wholes.  There are also cryptographic hashes, but those are even
// slower than MD5.
//

#ifndef FOLLY_SPOOKYHASH_H_
#define FOLLY_SPOOKYHASH_H_

#include <cstddef>
#include <cstdint>

namespace folly {
namespace hash {

class SpookyHash
{
public:
    //
    // SpookyHash: hash a single message in one call, produce 128-bit output
    //
    static void Hash128(
        const void *message,  // message to hash
        size_t length,        // length of message in bytes
        uint64_t *hash1,      // in/out: in seed 1, out hash value 1
        uint64_t *hash2);     // in/out: in seed 2, out hash value 2

    //
    // Hash64: hash a single message in one call, return 64-bit output
    //
    static uint64_t Hash64(
        const void *message,  // message to hash
        size_t length,        // length of message in bytes
        uint64_t seed)        // seed
    {
        uint64_t hash1 = seed;
        Hash128(message, length, &hash1, &seed);
        return hash1;
    }

    //
    // Hash32: hash a single message in one call, produce 32-bit output
    //
    static uint32_t Hash32(
        const void *message,  // message to hash
        size_t length,        // length of message in bytes
        uint32_t seed)        // seed
    {
        uint64_t hash1 = seed, hash2 = seed;
        Hash128(message, length, &hash1, &hash2);
        return (uint32_t)hash1;
    }

    //
    // Init: initialize the context of a SpookyHash
    //
    void Init(
        uint64_t seed1,     // any 64-bit value will do, including 0
        uint64_t seed2);    // different seeds produce independent hashes

    //
    // Update: add a piece of a message to a SpookyHash state
    //
    void Update(
        const void *message,  // message fragment
        size_t length);       // length of message fragment in bytes


    //
    // Final: compute the hash for the current SpookyHash state
    //
    // This does not modify the state; you can keep updating it afterward
    //
    // The result is the same as if SpookyHash() had been called with
    // all the pieces concatenated into one message.
    //
    void Final(
        uint64_t *hash1,  // out only: first 64 bits of hash value.
        uint64_t *hash2); // out only: second 64 bits of hash value.

    //
    // left rotate a 64-bit value by k bytes
    //
    static inline uint64_t Rot64(uint64_t x, int k)
    {
        return (x << k) | (x >> (64 - k));
    }

    //
    // This is used if the input is 96 bytes long or longer.
    //
    // The internal state is fully overwritten every 96 bytes.
    // Every input bit appears to cause at least 128 bits of entropy
    // before 96 other bytes are combined, when run forward or backward
    //   For every input bit,
    //   Two inputs differing in just that input bit
    //   Where "differ" means xor or subtraction
    //   And the base value is random
    //   When run forward or backwards one Mix
    // I tried 3 pairs of each; they all differed by at least 212 bits.
    //
    static inline void Mix(
        const uint64_t *data,
        uint64_t &s0, uint64_t &s1, uint64_t &s2, uint64_t &s3,
        uint64_t &s4, uint64_t &s5, uint64_t &s6, uint64_t &s7,
        uint64_t &s8, uint64_t &s9, uint64_t &s10,uint64_t &s11)
    {
      s0 += data[0];    s2 ^= s10;    s11 ^= s0;    s0 = Rot64(s0,11);    s11 += s1;
      s1 += data[1];    s3 ^= s11;    s0 ^= s1;    s1 = Rot64(s1,32);    s0 += s2;
      s2 += data[2];    s4 ^= s0;    s1 ^= s2;    s2 = Rot64(s2,43);    s1 += s3;
      s3 += data[3];    s5 ^= s1;    s2 ^= s3;    s3 = Rot64(s3,31);    s2 += s4;
      s4 += data[4];    s6 ^= s2;    s3 ^= s4;    s4 = Rot64(s4,17);    s3 += s5;
      s5 += data[5];    s7 ^= s3;    s4 ^= s5;    s5 = Rot64(s5,28);    s4 += s6;
      s6 += data[6];    s8 ^= s4;    s5 ^= s6;    s6 = Rot64(s6,39);    s5 += s7;
      s7 += data[7];    s9 ^= s5;    s6 ^= s7;    s7 = Rot64(s7,57);    s6 += s8;
      s8 += data[8];    s10 ^= s6;    s7 ^= s8;    s8 = Rot64(s8,55);    s7 += s9;
      s9 += data[9];    s11 ^= s7;    s8 ^= s9;    s9 = Rot64(s9,54);    s8 += s10;
      s10 += data[10];    s0 ^= s8;    s9 ^= s10;    s10 = Rot64(s10,22);    s9 += s11;
      s11 += data[11];    s1 ^= s9;    s10 ^= s11;    s11 = Rot64(s11,46);    s10 += s0;
    }

    //
    // Mix all 12 inputs together so that h0, h1 are a hash of them all.
    //
    // For two inputs differing in just the input bits
    // Where "differ" means xor or subtraction
    // And the base value is random, or a counting value starting at that bit
    // The final result will have each bit of h0, h1 flip
    // For every input bit,
    // with probability 50 +- .3%
    // For every pair of input bits,
    // with probability 50 +- 3%
    //
    // This does not rely on the last Mix() call having already mixed some.
    // Two iterations was almost good enough for a 64-bit result, but a
    // 128-bit result is reported, so End() does three iterations.
    //
    static inline void EndPartial(
        uint64_t &h0, uint64_t &h1, uint64_t &h2, uint64_t &h3,
        uint64_t &h4, uint64_t &h5, uint64_t &h6, uint64_t &h7,
        uint64_t &h8, uint64_t &h9, uint64_t &h10,uint64_t &h11)
    {
        h11+= h1;    h2 ^= h11;   h1 = Rot64(h1,44);
        h0 += h2;    h3 ^= h0;    h2 = Rot64(h2,15);
        h1 += h3;    h4 ^= h1;    h3 = Rot64(h3,34);
        h2 += h4;    h5 ^= h2;    h4 = Rot64(h4,21);
        h3 += h5;    h6 ^= h3;    h5 = Rot64(h5,38);
        h4 += h6;    h7 ^= h4;    h6 = Rot64(h6,33);
        h5 += h7;    h8 ^= h5;    h7 = Rot64(h7,10);
        h6 += h8;    h9 ^= h6;    h8 = Rot64(h8,13);
        h7 += h9;    h10^= h7;    h9 = Rot64(h9,38);
        h8 += h10;   h11^= h8;    h10= Rot64(h10,53);
        h9 += h11;   h0 ^= h9;    h11= Rot64(h11,42);
        h10+= h0;    h1 ^= h10;   h0 = Rot64(h0,54);
    }

    static inline void End(
        uint64_t &h0, uint64_t &h1, uint64_t &h2, uint64_t &h3,
        uint64_t &h4, uint64_t &h5, uint64_t &h6, uint64_t &h7,
        uint64_t &h8, uint64_t &h9, uint64_t &h10,uint64_t &h11)
    {
        EndPartial(h0,h1,h2,h3,h4,h5,h6,h7,h8,h9,h10,h11);
        EndPartial(h0,h1,h2,h3,h4,h5,h6,h7,h8,h9,h10,h11);
        EndPartial(h0,h1,h2,h3,h4,h5,h6,h7,h8,h9,h10,h11);
    }

    //
    // The goal is for each bit of the input to expand into 128 bits of
    //   apparent entropy before it is fully overwritten.
    // n trials both set and cleared at least m bits of h0 h1 h2 h3
    //   n: 2   m: 29
    //   n: 3   m: 46
    //   n: 4   m: 57
    //   n: 5   m: 107
    //   n: 6   m: 146
    //   n: 7   m: 152
    // when run forwards or backwards
    // for all 1-bit and 2-bit diffs
    // with diffs defined by either xor or subtraction
    // with a base of all zeros plus a counter, or plus another bit, or random
    //
    static inline void ShortMix(uint64_t &h0, uint64_t &h1, uint64_t &h2, uint64_t &h3)
    {
        h2 = Rot64(h2,50);  h2 += h3;  h0 ^= h2;
        h3 = Rot64(h3,52);  h3 += h0;  h1 ^= h3;
        h0 = Rot64(h0,30);  h0 += h1;  h2 ^= h0;
        h1 = Rot64(h1,41);  h1 += h2;  h3 ^= h1;
        h2 = Rot64(h2,54);  h2 += h3;  h0 ^= h2;
        h3 = Rot64(h3,48);  h3 += h0;  h1 ^= h3;
        h0 = Rot64(h0,38);  h0 += h1;  h2 ^= h0;
        h1 = Rot64(h1,37);  h1 += h2;  h3 ^= h1;
        h2 = Rot64(h2,62);  h2 += h3;  h0 ^= h2;
        h3 = Rot64(h3,34);  h3 += h0;  h1 ^= h3;
        h0 = Rot64(h0,5);   h0 += h1;  h2 ^= h0;
        h1 = Rot64(h1,36);  h1 += h2;  h3 ^= h1;
    }

    //
    // Mix all 4 inputs together so that h0, h1 are a hash of them all.
    //
    // For two inputs differing in just the input bits
    // Where "differ" means xor or subtraction
    // And the base value is random, or a counting value starting at that bit
    // The final result will have each bit of h0, h1 flip
    // For every input bit,
    // with probability 50 +- .3% (it is probably better than that)
    // For every pair of input bits,
    // with probability 50 +- .75% (the worst case is approximately that)
    //
    static inline void ShortEnd(uint64_t &h0, uint64_t &h1, uint64_t &h2, uint64_t &h3)
    {
        h3 ^= h2;  h2 = Rot64(h2,15);  h3 += h2;
        h0 ^= h3;  h3 = Rot64(h3,52);  h0 += h3;
        h1 ^= h0;  h0 = Rot64(h0,26);  h1 += h0;
        h2 ^= h1;  h1 = Rot64(h1,51);  h2 += h1;
        h3 ^= h2;  h2 = Rot64(h2,28);  h3 += h2;
        h0 ^= h3;  h3 = Rot64(h3,9);   h0 += h3;
        h1 ^= h0;  h0 = Rot64(h0,47);  h1 += h0;
        h2 ^= h1;  h1 = Rot64(h1,54);  h2 += h1;
        h3 ^= h2;  h2 = Rot64(h2,32);  h3 += h2;
        h0 ^= h3;  h3 = Rot64(h3,25);  h0 += h3;
        h1 ^= h0;  h0 = Rot64(h0,63);  h1 += h0;
    }

private:

    //
    // Short is used for messages under 192 bytes in length
    // Short has a low startup cost, the normal mode is good for long
    // keys, the cost crossover is at about 192 bytes.  The two modes were
    // held to the same quality bar.
    //
    static void Short(
        const void *message,  // message (array of bytes, not necessarily aligned)
        size_t length,        // length of message (in bytes)
        uint64_t *hash1,      // in/out: in the seed, out the hash value
        uint64_t *hash2);     // in/out: in the seed, out the hash value

    // number of uint64_t's in internal state
    static const size_t sc_numVars = 12;

    // size of the internal state
    static const size_t sc_blockSize = sc_numVars*8;

    // size of buffer of unhashed data, in bytes
    static const size_t sc_bufSize = 2*sc_blockSize;

    //
    // sc_const: a constant which:
    //  * is not zero
    //  * is odd
    //  * is a not-very-regular mix of 1's and 0's
    //  * does not need any other special mathematical properties
    //
    static const uint64_t sc_const = 0xdeadbeefdeadbeefLL;

    uint64_t m_data[2*sc_numVars];  // unhashed data, for partial messages
    uint64_t m_state[sc_numVars];   // internal state of the hash
    size_t m_length;                // total length of the input so far
    uint8_t  m_remainder;           // length of unhashed data stashed in m_data
};

}  // namespace hash
}  // namespace folly

#endif