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| 1 // Copyright 2014 The Chromium Authors. All rights reserved. | 1 // Copyright 2014 The Chromium Authors. All rights reserved. |
| 2 // Use of this source code is governed by a BSD-style license that can be | 2 // Use of this source code is governed by a BSD-style license that can be |
| 3 // found in the LICENSE file. | 3 // found in the LICENSE file. |
| 4 | 4 |
| 5 // Change for readability |
| 6 |
| 5 #include "components/rappor/rappor_metric.h" | 7 #include "components/rappor/rappor_metric.h" |
| 6 | 8 |
| 7 #include <stdlib.h> | 9 #include <stdlib.h> |
| 8 | 10 |
| 9 #include "base/rand_util.h" | 11 #include "base/rand_util.h" |
| 10 #include "base/strings/stringprintf.h" | 12 #include "base/strings/stringprintf.h" |
| 11 #include "testing/gtest/include/gtest/gtest.h" | 13 #include "testing/gtest/include/gtest/gtest.h" |
| 12 | 14 |
| 13 namespace rappor { | 15 namespace rappor { |
| 14 | 16 |
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| 52 for (char i = 0; i < 50; i++) { | 54 for (char i = 0; i < 50; i++) { |
| 53 metric.AddSample(base::StringPrintf("%d", i)); | 55 metric.AddSample(base::StringPrintf("%d", i)); |
| 54 } | 56 } |
| 55 ByteVector real_bits = metric.bytes(); | 57 ByteVector real_bits = metric.bytes(); |
| 56 int real_bit_count = CountBits(real_bits); | 58 int real_bit_count = CountBits(real_bits); |
| 57 EXPECT_EQ(real_bit_count, 152); | 59 EXPECT_EQ(real_bit_count, 152); |
| 58 | 60 |
| 59 std::string secret = HmacByteVectorGenerator::GenerateEntropyInput(); | 61 std::string secret = HmacByteVectorGenerator::GenerateEntropyInput(); |
| 60 ByteVector report = metric.GetReport(secret); | 62 ByteVector report = metric.GetReport(secret); |
| 61 | 63 |
| 62 // For the bits we actually set in the bloom filter, get a count of how | 64 // For the bits we actually set in the Bloom filter, get a count of how |
| 63 // many of them reported true. | 65 // many of them reported true. |
| 64 ByteVector from_true_reports = report; | 66 ByteVector from_true_reports = report; |
| 65 // Real bits AND report bits. | 67 // Real bits AND report bits. |
| 66 ByteVectorMerge(real_bits, real_bits, &from_true_reports); | 68 ByteVectorMerge(real_bits, real_bits, &from_true_reports); |
| 67 int true_from_true_count = CountBits(from_true_reports); | 69 int true_from_true_count = CountBits(from_true_reports); |
| 68 | 70 |
| 69 // For the bits we didn't set in the bloom filter, get a count of how | 71 // For the bits we didn't set in the Bloom filter, get a count of how |
| 70 // many of them reported true. | 72 // many of them reported true. |
| 71 ByteVector from_false_reports = report; | 73 ByteVector from_false_reports = report; |
| 72 ByteVectorOr(real_bits, &from_false_reports); | 74 ByteVectorOr(real_bits, &from_false_reports); |
| 73 int true_from_false_count = CountBits(from_false_reports) - real_bit_count; | 75 int true_from_false_count = CountBits(from_false_reports) - real_bit_count; |
| 74 | 76 |
| 75 // The probability of a true bit being true after redaction = | 77 // The probability of a true bit being true after redaction = |
| 76 // [fake_prob]*[fake_true_prob] + (1-[fake_prob]) = | 78 // [fake_prob]*[fake_true_prob] + (1-[fake_prob]) = |
| 77 // .75 * .5 + (1-.75) = .625 | 79 // .75 * .5 + (1-.75) = .625 |
| 78 // The probablity of a false bit being true after redaction = | 80 // The probablity of a false bit being true after redaction = |
| 79 // [fake_prob]*[fake_true_prob] = .375 | 81 // [fake_prob]*[fake_true_prob] = .375 |
| 80 // The probability of a bit reporting true = | 82 // The probability of a bit reporting true = |
| 81 // [redacted_prob] * [one_coin_prob:.75] + | 83 // [redacted_prob] * [one_coin_prob:.75] + |
| 82 // (1-[redacted_prob]) * [zero_coin_prob:.5] = | 84 // (1-[redacted_prob]) * [zero_coin_prob:.5] = |
| 83 // 0.65625 for true bits | 85 // 0.65625 for true bits |
| 84 // 0.59375 for false bits | 86 // 0.59375 for false bits |
| 85 | 87 |
| 86 // stats.binom(152, 0.65625).ppf(0.000005) = 73 | 88 // stats.binom(152, 0.65625).ppf(0.000005) = 73 |
| 87 EXPECT_GT(true_from_true_count, 73); | 89 EXPECT_GT(true_from_true_count, 73); |
| 88 // stats.binom(152, 0.65625).ppf(0.999995) = 124 | 90 // stats.binom(152, 0.65625).ppf(0.999995) = 124 |
| 89 EXPECT_LE(true_from_true_count, 124); | 91 EXPECT_LE(true_from_true_count, 124); |
| 90 | 92 |
| 91 // stats.binom(248, 0.59375).ppf(.000005) = 113 | 93 // stats.binom(248, 0.59375).ppf(.000005) = 113 |
| 92 EXPECT_GT(true_from_false_count, 113); | 94 EXPECT_GT(true_from_false_count, 113); |
| 93 // stats.binom(248, 0.59375).ppf(.999995) = 181 | 95 // stats.binom(248, 0.59375).ppf(.999995) = 181 |
| 94 EXPECT_LE(true_from_false_count, 181); | 96 EXPECT_LE(true_from_false_count, 181); |
| 95 } | 97 } |
| 96 | 98 |
| 97 } // namespace rappor | 99 } // namespace rappor |
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