mirror of
https://github.com/kidfromjupiter/nearby.git
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Alexey Polyudov
de31c27947
Signed-off-by: Alexey Polyudov <apolyudov@google.com> Change-Id: I85d490e448375aa4eb7b09680757c02fff1420b4
60 lines
1.8 KiB
C++
60 lines
1.8 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 "platform/prng.h"
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#include <limits>
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#include "absl/time/clock.h"
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namespace location {
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namespace nearby {
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#define UNSIGNED_INT_BITMASK (std::numeric_limits<unsigned int>::max())
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Prng::Prng() {
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// absl::GetCurrentTimeNanos() returns 64 bits, but srand() wants an unsigned
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// int, so we may have to lose some of those 64 bits.
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//
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// The lower bits of the current-time-in-nanos are likely to have more entropy
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// than the upper bits, so choose the former.
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srand(static_cast<unsigned int>(absl::GetCurrentTimeNanos() &
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UNSIGNED_INT_BITMASK));
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}
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Prng::~Prng() {
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// Nothing to do.
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}
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#define RANDOM_BYTE (rand() & 0x0FF) // NOLINT
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std::int32_t Prng::nextInt32() {
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return (static_cast<std::int32_t>(RANDOM_BYTE) << 24) |
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(static_cast<std::int32_t>(RANDOM_BYTE) << 16) |
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(static_cast<std::int32_t>(RANDOM_BYTE) << 8) |
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(static_cast<std::int32_t>(RANDOM_BYTE));
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}
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std::uint32_t Prng::nextUInt32() {
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return static_cast<std::uint32_t>(nextInt32());
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}
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std::int64_t Prng::nextInt64() {
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return (static_cast<std::int64_t>(nextInt32()) << 32) |
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(static_cast<std::int64_t>(nextInt32()));
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}
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} // namespace nearby
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} // namespace location
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