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Diffstat (limited to 'services/surfaceflinger/DisplayHardware/Hash.cpp')
| -rw-r--r-- | services/surfaceflinger/DisplayHardware/Hash.cpp | 93 |
1 files changed, 93 insertions, 0 deletions
diff --git a/services/surfaceflinger/DisplayHardware/Hash.cpp b/services/surfaceflinger/DisplayHardware/Hash.cpp new file mode 100644 index 0000000000..6056c8d6f8 --- /dev/null +++ b/services/surfaceflinger/DisplayHardware/Hash.cpp @@ -0,0 +1,93 @@ +/* + * Copyright 2021 The Android Open Source Project + * + * Licensed under the Apache License, Version 2.0 (the "License"); + * you may not use this file except in compliance with the License. + * You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +#undef LOG_TAG +#define LOG_TAG "DisplayIdentification" + +#include <cstring> +#include <type_traits> + +#include <log/log.h> + +#include "Hash.h" + +namespace android { +namespace { + +template <class T> +inline T load(const void* p) { + static_assert(std::is_integral<T>::value, "T must be integral"); + + T r; + std::memcpy(&r, p, sizeof(r)); + return r; +} + +uint64_t rotateByAtLeast1(uint64_t val, uint8_t shift) { + return (val >> shift) | (val << (64 - shift)); +} + +uint64_t shiftMix(uint64_t val) { + return val ^ (val >> 47); +} + +uint64_t hash64Len16(uint64_t u, uint64_t v) { + constexpr uint64_t kMul = 0x9ddfea08eb382d69; + uint64_t a = (u ^ v) * kMul; + a ^= (a >> 47); + uint64_t b = (v ^ a) * kMul; + b ^= (b >> 47); + b *= kMul; + return b; +} + +uint64_t hash64Len0To16(const char* s, uint64_t len) { + constexpr uint64_t k2 = 0x9ae16a3b2f90404f; + constexpr uint64_t k3 = 0xc949d7c7509e6557; + + if (len > 8) { + const uint64_t a = load<uint64_t>(s); + const uint64_t b = load<uint64_t>(s + len - 8); + return hash64Len16(a, rotateByAtLeast1(b + len, static_cast<uint8_t>(len))) ^ b; + } + if (len >= 4) { + const uint32_t a = load<uint32_t>(s); + const uint32_t b = load<uint32_t>(s + len - 4); + return hash64Len16(len + (a << 3), b); + } + if (len > 0) { + const unsigned char a = static_cast<unsigned char>(s[0]); + const unsigned char b = static_cast<unsigned char>(s[len >> 1]); + const unsigned char c = static_cast<unsigned char>(s[len - 1]); + const uint32_t y = static_cast<uint32_t>(a) + (static_cast<uint32_t>(b) << 8); + const uint32_t z = static_cast<uint32_t>(len) + (static_cast<uint32_t>(c) << 2); + return shiftMix(y * k2 ^ z * k3) * k2; + } + return k2; +} + +} // namespace + +uint64_t cityHash64Len0To16(std::string_view sv) { + auto len = sv.length(); + if (len > 16) { + ALOGE("%s called with length %zu. Only hashing the first 16 chars", __FUNCTION__, len); + len = 16; + } + return hash64Len0To16(sv.data(), len); +} + +} // namespace android
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