CodeDweller/mishmash.cpp

// mishmash.cpp
//
// Copyright (C) 2019-2020 MicroNeil Research Corporation.
//
// This software is released under the MIT license. See LICENSE.TXT.
//
// Mishmash is a non-cryptographic hash optimized for short strings.

#include "mishmash.hpp"

namespace codedweller {

uint32_t primes[256] {
    1019,   1021,   1031,   1033,   1039,   1049,   1051,   1061,
    1063,   1069,   1087,   1091,   1093,   1097,   1103,   1109,
    1117,   1123,   1129,   1151,   1153,   1163,   1171,   1181,
    1187,   1193,   1201,   1213,   1217,   1223,   1229,   1231,
    1237,   1249,   1259,   1277,   1279,   1283,   1289,   1291,
    1297,   1301,   1303,   1307,   1319,   1321,   1327,   1361,
    1367,   1373,   1381,   1399,   1409,   1423,   1427,   1429,
    1433,   1439,   1447,   1451,   1453,   1459,   1471,   1481,

    1483,   1487,   1489,   1493,   1499,   1511,   1523,   1531,
    1543,   1549,   1553,   1559,   1567,   1571,   1579,   1583,
    1597,   1601,   1607,   1609,   1613,   1619,   1621,   1627,
    1637,   1657,   1663,   1667,   1669,   1693,   1697,   1699,
    1709,   1721,   1723,   1733,   1741,   1747,   1753,   1759,
    1777,   1783,   1787,   1789,   1801,   1811,   1823,   1831,
    1847,   1861,   1867,   1871,   1873,   1877,   1879,   1889,
    1901,   1907,   1913,   1931,   1933,   1949,   1951,   1973,

    1979,   1987,   1993,   1997,   1999,   2003,   2011,   2017,
    2027,   2029,   2039,   2053,   2063,   2069,   2081,   2083,
    2087,   2089,   2099,   2111,   2113,   2129,   2131,   2137,
    2141,   2143,   2153,   2161,   2179,   2203,   2207,   2213,
    2221,   2237,   2239,   2243,   2251,   2267,   2269,   2273,
    2281,   2287,   2293,   2297,   2309,   2311,   2333,   2339,
    2341,   2347,   2351,   2357,   2371,   2377,   2381,   2383,
    2389,   2393,   2399,   2411,   2417,   2423,   2437,   2441,
    
    2447,   2459,   2467,   2473,   2477,   2503,   2521,   2531,
    2539,   2543,   2549,   2551,   2557,   2579,   2591,   2593,
    2609,   2617,   2621,   2633,   2647,   2657,   2659,   2663,
    2671,   2677,   2683,   2687,   2689,   2693,   2699,   2707,
    2711,   2713,   2719,   2729,   2731,   2741,   2749,   2753,
    2767,   2777,   2789,   2791,   2797,   2801,   2803,   2819,
    2833,   2837,   2843,   2851,   2857,   2861,   2879,   2887,
    2897,   2903,   2909,   2917,   2927,   2939,   2953,   2957
};


inline size_t mod256(size_t n) noexcept { return (n & 0xff); }

inline uint32_t selectedPrime(size_t n) noexcept { return primes[mod256(n)]; }

uint32_t mishmash(const unsigned char* buffer, size_t length) noexcept {
    uint64_t accumulator = selectedPrime(length);
    for(size_t index = 0; index < length; index++) {
        unsigned char byte = buffer[index];
        accumulator += selectedPrime(index + accumulator);
        accumulator *= selectedPrime(byte + accumulator);
        accumulator += accumulator >> 32;
        accumulator &= 0x00000fffffffffff;
    }
    return accumulator & 0x00000000ffffffff;
}

uint32_t mishmash(const std::string& s) noexcept { 
    return mishmash((const unsigned char*) s.c_str(), s.length()); 
}

uint32_t mishmash(const std::vector<unsigned char>& v) noexcept { 
    return mishmash(v.data(), v.size()); 
}

}