41 lines
1.3 KiB
C++
41 lines
1.3 KiB
C++
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// Copyright 2015 Google Inc. All rights reserved.
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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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#include "unix_kernel_rand_impl.h"
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#include <stdint.h> // uint64_t
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namespace rappor {
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const int kMaxBitWidth = 32; // also in encoder.cc
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bool UnixKernelRand::GetMask(float prob, int num_bits, Bits* mask_out) const {
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uint8_t rand_buf[kMaxBitWidth];
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size_t num_elems = fread(&rand_buf, sizeof(uint8_t), num_bits, fp_);
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if (num_elems != static_cast<size_t>(num_bits)) { // fread error
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return false;
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}
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uint8_t threshold_256 = static_cast<uint8_t>(prob * 256);
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Bits mask = 0;
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for (int i = 0; i < num_bits; ++i) {
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uint8_t bit = (rand_buf[i] < threshold_256);
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mask |= (bit << i);
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}
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*mask_out = mask;
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return true;
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}
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} // namespace rappor
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