mirror of
https://github.com/kidfromjupiter/nearby.git
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72 lines
2.1 KiB
C++
72 lines
2.1 KiB
C++
// Copyright 2020 Google LLC
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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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// https://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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#include "internal/platform/byte_utils.h"
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#include <cstdint>
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#include <cstdlib>
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#include <string>
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#include "absl/strings/str_format.h"
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#include "internal/platform/byte_array.h"
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#include "internal/platform/stream_reader.h"
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namespace nearby {
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namespace byte_utils {
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namespace {
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// The biggest prime number under 10000, used as a mod base to trim integers
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// into 4 digits.
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constexpr int kHashBasePrime = 9973;
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// The hash multiplier.
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constexpr int kHashBaseMultiplier = 31;
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} // namespace
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std::string ToFourDigitString(const ByteArray& bytes) {
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int multiplier = 1;
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int hashCode = 0;
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StreamReader stream_reader{&bytes};
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while (stream_reader.IsAvailable(1)) {
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auto byte = stream_reader.ReadInt8().value_or(0);
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hashCode = (hashCode + byte * multiplier) % kHashBasePrime;
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multiplier = multiplier * kHashBaseMultiplier % kHashBasePrime;
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}
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return absl::StrFormat("%04d", abs(hashCode));
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}
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int32_t BytesToInt(const ByteArray& bytes) {
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const char* int_bytes = bytes.data();
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int32_t result = 0;
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for (int i = 0; i < bytes.size() && i < 4; ++i) {
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result <<= 8;
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result |= static_cast<int32_t>(int_bytes[i]) & 0x0FF;
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}
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return result;
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}
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ByteArray IntToBytes(int32_t value) {
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ByteArray result(sizeof(int32_t));
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char* buffer = result.data();
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buffer[0] = static_cast<char>((value >> 24) & 0x0FF);
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buffer[1] = static_cast<char>((value >> 16) & 0x0FF);
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buffer[2] = static_cast<char>((value >> 8) & 0x0FF);
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buffer[3] = static_cast<char>(value & 0x0FF);
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return result;
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}
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} // namespace byte_utils
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} // namespace nearby
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