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93 lines
2.6 KiB
93 lines
2.6 KiB
/*
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* Copyright 2021 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#undef LOG_TAG
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#define LOG_TAG "DisplayIdentification"
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#include <cstring>
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#include <type_traits>
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#include <log/log.h>
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#include "Hash.h"
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namespace android {
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namespace {
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template <class T>
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inline T load(const void* p) {
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static_assert(std::is_integral<T>::value, "T must be integral");
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T r;
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std::memcpy(&r, p, sizeof(r));
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return r;
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}
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uint64_t rotateByAtLeast1(uint64_t val, uint8_t shift) {
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return (val >> shift) | (val << (64 - shift));
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}
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uint64_t shiftMix(uint64_t val) {
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return val ^ (val >> 47);
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}
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uint64_t hash64Len16(uint64_t u, uint64_t v) {
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constexpr uint64_t kMul = 0x9ddfea08eb382d69;
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uint64_t a = (u ^ v) * kMul;
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a ^= (a >> 47);
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uint64_t b = (v ^ a) * kMul;
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b ^= (b >> 47);
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b *= kMul;
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return b;
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}
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uint64_t hash64Len0To16(const char* s, uint64_t len) {
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constexpr uint64_t k2 = 0x9ae16a3b2f90404f;
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constexpr uint64_t k3 = 0xc949d7c7509e6557;
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if (len > 8) {
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const uint64_t a = load<uint64_t>(s);
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const uint64_t b = load<uint64_t>(s + len - 8);
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return hash64Len16(a, rotateByAtLeast1(b + len, static_cast<uint8_t>(len))) ^ b;
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}
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if (len >= 4) {
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const uint32_t a = load<uint32_t>(s);
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const uint32_t b = load<uint32_t>(s + len - 4);
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return hash64Len16(len + (a << 3), b);
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}
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if (len > 0) {
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const unsigned char a = static_cast<unsigned char>(s[0]);
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const unsigned char b = static_cast<unsigned char>(s[len >> 1]);
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const unsigned char c = static_cast<unsigned char>(s[len - 1]);
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const uint32_t y = static_cast<uint32_t>(a) + (static_cast<uint32_t>(b) << 8);
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const uint32_t z = static_cast<uint32_t>(len) + (static_cast<uint32_t>(c) << 2);
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return shiftMix(y * k2 ^ z * k3) * k2;
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}
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return k2;
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}
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} // namespace
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uint64_t cityHash64Len0To16(std::string_view sv) {
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auto len = sv.length();
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if (len > 16) {
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ALOGE("%s called with length %zu. Only hashing the first 16 chars", __FUNCTION__, len);
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len = 16;
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}
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return hash64Len0To16(sv.data(), len);
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}
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} // namespace android
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