80 lines
2.0 KiB
C++
80 lines
2.0 KiB
C++
#pragma once
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#include <cstdint>
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#include <cstddef>
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namespace halfsiphash {
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namespace detail {
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constexpr uint32_t rotl(uint32_t x, int b) {
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return (x << b) | (x >> (32 - b));
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}
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constexpr uint32_t load_le32(const uint8_t *p) {
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return static_cast<uint32_t>(p[0])
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}
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inline void store_le32(uint8_t *p, uint32_t v) {
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p[0] = static_cast<uint8_t>(v);
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p[1] = static_cast<uint8_t>(v >> 8);
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p[2] = static_cast<uint8_t>(v >> 16);
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p[3] = static_cast<uint8_t>(v >> 24);
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}
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inline void sipround(uint32_t &v0, uint32_t &v1, uint32_t &v2, uint32_t &v3) {
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v0 += v1; v1 = rotl(v1, 5); v1 ^= v0; v0 = rotl(v0, 16);
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v2 += v3; v3 = rotl(v3, 8); v3 ^= v2;
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v0 += v3; v3 = rotl(v3, 7); v3 ^= v0;
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v2 += v1; v1 = rotl(v1, 13); v1 ^= v2; v2 = rotl(v2, 16);
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}
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} // namespace detail
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// Compute HalfSipHash-2-4 with an 8-byte key, returning a 32-bit hash.
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inline uint32_t hash32(const uint8_t *data, size_t len, const uint8_t key[8]) {
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using namespace detail;
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uint32_t k0 = load_le32(key);
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uint32_t k1 = load_le32(key + 4);
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uint32_t v0 = 0 ^ k0;
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uint32_t v1 = 0 ^ k1;
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uint32_t v2 = UINT32_C(0x6c796765) ^ k0;
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uint32_t v3 = UINT32_C(0x74656462) ^ k1;
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const uint8_t *end = data + len - (len % 4);
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for (const uint8_t *p = data; p != end; p += 4) {
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uint32_t m = load_le32(p);
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v3 ^= m;
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sipround(v0, v1, v2, v3);
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sipround(v0, v1, v2, v3);
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v0 ^= m;
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}
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uint32_t b = static_cast<uint32_t>(len) << 24;
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switch (len & 3) {
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case 3: b |= static_cast<uint32_t>(end[2]) << 16; [[fallthrough]];
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case 2: b |= static_cast<uint32_t>(end[1]) << 8; [[fallthrough]];
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case 1: b |= static_cast<uint32_t>(end[0]); break;
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case 0: break;
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}
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v3 ^= b;
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sipround(v0, v1, v2, v3);
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sipround(v0, v1, v2, v3);
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v0 ^= b;
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v2 ^= 0xff;
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sipround(v0, v1, v2, v3);
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sipround(v0, v1, v2, v3);
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sipround(v0, v1, v2, v3);
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sipround(v0, v1, v2, v3);
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return v1 ^ v3;
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}
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} // namespace halfsiphash
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