citra/src/common/hash.cpp

// Copyright 2015 Citra Emulator Project
// Licensed under GPLv2 or any later version
// Refer to the license.txt file included.

#if defined(_MSC_VER)
#include <stdlib.h>
#endif

#include "common_funcs.h"
#include "common_types.h"
#include "hash.h"

namespace Common {

// MurmurHash3 was written by Austin Appleby, and is placed in the public
// domain. The author hereby disclaims copyright to this source code.

// Block read - if your platform needs to do endian-swapping or can only handle aligned reads, do
// the conversion here
static FORCE_INLINE u64 getblock64(const u64* p, int i) {
    return p[i];
}

// Finalization mix - force all bits of a hash block to avalanche
static FORCE_INLINE u64 fmix64(u64 k) {
    k ^= k >> 33;
    k *= 0xff51afd7ed558ccdllu;
    k ^= k >> 33;
    k *= 0xc4ceb9fe1a85ec53llu;
    k ^= k >> 33;

    return k;
}

// This is the 128-bit variant of the MurmurHash3 hash function that is targetted for 64-bit
// platforms (MurmurHash3_x64_128). It was taken from:
// https://code.google.com/p/smhasher/source/browse/trunk/MurmurHash3.cpp
void MurmurHash3_128(const void* key, int len, u32 seed, void* out) {
    const u8 * data = (const u8*)key;
    const int nblocks = len / 16;

    u64 h1 = seed;
    u64 h2 = seed;

    const u64 c1 = 0x87c37b91114253d5llu;
    const u64 c2 = 0x4cf5ad432745937fllu;

    // Body

    const u64 * blocks = (const u64 *)(data);

    for (int i = 0; i < nblocks; i++) {
        u64 k1 = getblock64(blocks,i*2+0);
        u64 k2 = getblock64(blocks,i*2+1);

        k1 *= c1; k1  = _rotl64(k1,31); k1 *= c2; h1 ^= k1;

        h1 = _rotl64(h1,27); h1 += h2; h1 = h1*5+0x52dce729;

        k2 *= c2; k2  = _rotl64(k2,33); k2 *= c1; h2 ^= k2;

        h2 = _rotl64(h2,31); h2 += h1; h2 = h2*5+0x38495ab5;
    }

    // Tail

    const u8 * tail = (const u8*)(data + nblocks*16);

    u64 k1 = 0;
    u64 k2 = 0;

    switch (len & 15) {
    case 15: k2 ^= ((u64)tail[14]) << 48;
    case 14: k2 ^= ((u64)tail[13]) << 40;
    case 13: k2 ^= ((u64)tail[12]) << 32;
    case 12: k2 ^= ((u64)tail[11]) << 24;
    case 11: k2 ^= ((u64)tail[10]) << 16;
    case 10: k2 ^= ((u64)tail[ 9]) << 8;
    case  9: k2 ^= ((u64)tail[ 8]) << 0;
        k2 *= c2; k2  = _rotl64(k2,33); k2 *= c1; h2 ^= k2;

    case  8: k1 ^= ((u64)tail[ 7]) << 56;
    case  7: k1 ^= ((u64)tail[ 6]) << 48;
    case  6: k1 ^= ((u64)tail[ 5]) << 40;
    case  5: k1 ^= ((u64)tail[ 4]) << 32;
    case  4: k1 ^= ((u64)tail[ 3]) << 24;
    case  3: k1 ^= ((u64)tail[ 2]) << 16;
    case  2: k1 ^= ((u64)tail[ 1]) << 8;
    case  1: k1 ^= ((u64)tail[ 0]) << 0;
        k1 *= c1; k1  = _rotl64(k1,31); k1 *= c2; h1 ^= k1;
    };

    // Finalization

    h1 ^= len; h2 ^= len;

    h1 += h2;
    h2 += h1;

    h1 = fmix64(h1);
    h2 = fmix64(h2);

    h1 += h2;
    h2 += h1;

    ((u64*)out)[0] = h1;
    ((u64*)out)[1] = h2;
}

} // namespace Common