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085973a486
The murmurhash implementation tries to read a sequence of four bytes as a single little-endian uint32 value. This does not work on e.g. Linux/s390x; https://buildd.debian.org/status/fetch.php?pkg=kakoune&arch=s390x&ver=2021.11.08-1&stamp=1645975425&raw=0
90 lines
2.0 KiB
C++
90 lines
2.0 KiB
C++
#include "hash.hh"
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#include <cstdint>
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#include <cstring>
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#include "unit_tests.hh"
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#include "assert.hh"
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namespace Kakoune
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{
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[[gnu::always_inline]]
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static inline uint32_t rotl(uint32_t x, int8_t r)
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{
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return (x << r) | (x >> (32 - r));
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}
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[[gnu::always_inline]]
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static inline uint32_t fmix(uint32_t h)
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{
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h ^= h >> 16;
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h *= 0x85ebca6b;
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h ^= h >> 13;
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h *= 0xc2b2ae35;
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h ^= h >> 16;
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return h;
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}
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// murmur3 hash, based on https://github.com/PeterScott/murmur3
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size_t hash_data(const char* input, size_t len)
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{
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const uint8_t* data = reinterpret_cast<const uint8_t*>(input);
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uint32_t hash = 0x1235678;
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constexpr uint32_t c1 = 0xcc9e2d51;
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constexpr uint32_t c2 = 0x1b873593;
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const ptrdiff_t nblocks = len / 4;
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const uint8_t* blocks = data + nblocks*4;
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for (ptrdiff_t i = -nblocks; i; ++i)
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{
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uint32_t key;
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#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
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memcpy(&key, blocks + 4*i, 4);
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#else
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key = blocks[4*i] + (blocks[4*i + 1] << 8) + (blocks[4*i + 2] << 16) + (blocks[4*i + 3] << 24);
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#endif
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key *= c1;
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key = rotl(key, 15);
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key *= c2;
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hash ^= key;
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hash = rotl(hash, 13);
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hash = hash * 5 + 0xe6546b64;
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}
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const uint8_t* tail = data + nblocks * 4;
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uint32_t key = 0;
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switch (len & 0b11)
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{
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case 3: key ^= tail[2] << 16; [[fallthrough]];
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case 2: key ^= tail[1] << 8; [[fallthrough]];
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case 1: key ^= tail[0];
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key *= c1;
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key = rotl(key,15);
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key *= c2;
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hash ^= key;
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}
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hash ^= len;
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hash = fmix(hash);
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return hash;
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}
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UnitTest test_murmur_hash{[] {
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{
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constexpr char data[] = "Hello, World!";
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kak_assert(hash_data(data, strlen(data)) == 0xf816f95b);
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}
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{
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constexpr char data[] = "xxxxxxxxxxxxxxxxxxxxxxxxxxxx";
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kak_assert(hash_data(data, strlen(data)) == 3551113186);
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}
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kak_assert(hash_data("", 0) == 2572747774);
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}};
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}
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