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-rw-r--r--absl/random/internal/seed_material_test.cc201
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diff --git a/absl/random/internal/seed_material_test.cc b/absl/random/internal/seed_material_test.cc
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+// Copyright 2017 The Abseil Authors.
+//
+// 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
+//
+//      https://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.
+
+#include "absl/random/internal/seed_material.h"
+
+#include <bitset>
+#include <cstdlib>
+#include <cstring>
+#include <random>
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+
+#ifdef __ANDROID__
+// Android assert messages only go to system log, so death tests cannot inspect
+// the message for matching.
+#define ABSL_EXPECT_DEATH_IF_SUPPORTED(statement, regex) \
+  EXPECT_DEATH_IF_SUPPORTED(statement, ".*")
+#else
+#define ABSL_EXPECT_DEATH_IF_SUPPORTED EXPECT_DEATH_IF_SUPPORTED
+#endif
+
+namespace {
+
+using testing::Each;
+using testing::ElementsAre;
+using testing::Eq;
+using testing::Ne;
+using testing::Pointwise;
+
+TEST(SeedBitsToBlocks, VerifyCases) {
+  EXPECT_EQ(0, absl::random_internal::SeedBitsToBlocks(0));
+  EXPECT_EQ(1, absl::random_internal::SeedBitsToBlocks(1));
+  EXPECT_EQ(1, absl::random_internal::SeedBitsToBlocks(31));
+  EXPECT_EQ(1, absl::random_internal::SeedBitsToBlocks(32));
+  EXPECT_EQ(2, absl::random_internal::SeedBitsToBlocks(33));
+  EXPECT_EQ(4, absl::random_internal::SeedBitsToBlocks(127));
+  EXPECT_EQ(4, absl::random_internal::SeedBitsToBlocks(128));
+  EXPECT_EQ(5, absl::random_internal::SeedBitsToBlocks(129));
+}
+
+TEST(ReadSeedMaterialFromOSEntropy, SuccessiveReadsAreDistinct) {
+  constexpr size_t kSeedMaterialSize = 64;
+  uint32_t seed_material_1[kSeedMaterialSize] = {};
+  uint32_t seed_material_2[kSeedMaterialSize] = {};
+
+  EXPECT_TRUE(absl::random_internal::ReadSeedMaterialFromOSEntropy(
+      absl::Span<uint32_t>(seed_material_1, kSeedMaterialSize)));
+  EXPECT_TRUE(absl::random_internal::ReadSeedMaterialFromOSEntropy(
+      absl::Span<uint32_t>(seed_material_2, kSeedMaterialSize)));
+
+  EXPECT_THAT(seed_material_1, Pointwise(Ne(), seed_material_2));
+}
+
+TEST(ReadSeedMaterialFromOSEntropy, ReadZeroBytesIsNoOp) {
+  uint32_t seed_material[32] = {};
+  std::memset(seed_material, 0xAA, sizeof(seed_material));
+  EXPECT_TRUE(absl::random_internal::ReadSeedMaterialFromOSEntropy(
+      absl::Span<uint32_t>(seed_material, 0)));
+
+  EXPECT_THAT(seed_material, Each(Eq(0xAAAAAAAA)));
+}
+
+TEST(ReadSeedMaterialFromOSEntropy, NullPtrVectorArgument) {
+#ifdef NDEBUG
+  EXPECT_FALSE(absl::random_internal::ReadSeedMaterialFromOSEntropy(
+      absl::Span<uint32_t>(nullptr, 32)));
+#else
+  bool result;
+  ABSL_EXPECT_DEATH_IF_SUPPORTED(
+      result = absl::random_internal::ReadSeedMaterialFromOSEntropy(
+          absl::Span<uint32_t>(nullptr, 32)),
+      "!= nullptr");
+  (void)result;  // suppress unused-variable warning
+#endif
+}
+
+TEST(ReadSeedMaterialFromURBG, SeedMaterialEqualsVariateSequence) {
+  // Two default-constructed instances of std::mt19937_64 are guaranteed to
+  // produce equal variate-sequences.
+  std::mt19937 urbg_1;
+  std::mt19937 urbg_2;
+  constexpr size_t kSeedMaterialSize = 1024;
+  uint32_t seed_material[kSeedMaterialSize] = {};
+
+  EXPECT_TRUE(absl::random_internal::ReadSeedMaterialFromURBG(
+      &urbg_1, absl::Span<uint32_t>(seed_material, kSeedMaterialSize)));
+  for (uint32_t seed : seed_material) {
+    EXPECT_EQ(seed, urbg_2());
+  }
+}
+
+TEST(ReadSeedMaterialFromURBG, ReadZeroBytesIsNoOp) {
+  std::mt19937_64 urbg;
+  uint32_t seed_material[32];
+  std::memset(seed_material, 0xAA, sizeof(seed_material));
+  EXPECT_TRUE(absl::random_internal::ReadSeedMaterialFromURBG(
+      &urbg, absl::Span<uint32_t>(seed_material, 0)));
+
+  EXPECT_THAT(seed_material, Each(Eq(0xAAAAAAAA)));
+}
+
+TEST(ReadSeedMaterialFromURBG, NullUrbgArgument) {
+  constexpr size_t kSeedMaterialSize = 32;
+  uint32_t seed_material[kSeedMaterialSize];
+#ifdef NDEBUG
+  EXPECT_FALSE(absl::random_internal::ReadSeedMaterialFromURBG<std::mt19937_64>(
+      nullptr, absl::Span<uint32_t>(seed_material, kSeedMaterialSize)));
+#else
+  bool result;
+  ABSL_EXPECT_DEATH_IF_SUPPORTED(
+      result = absl::random_internal::ReadSeedMaterialFromURBG<std::mt19937_64>(
+          nullptr, absl::Span<uint32_t>(seed_material, kSeedMaterialSize)),
+      "!= nullptr");
+  (void)result;  // suppress unused-variable warning
+#endif
+}
+
+TEST(ReadSeedMaterialFromURBG, NullPtrVectorArgument) {
+  std::mt19937_64 urbg;
+#ifdef NDEBUG
+  EXPECT_FALSE(absl::random_internal::ReadSeedMaterialFromURBG(
+      &urbg, absl::Span<uint32_t>(nullptr, 32)));
+#else
+  bool result;
+  ABSL_EXPECT_DEATH_IF_SUPPORTED(
+      result = absl::random_internal::ReadSeedMaterialFromURBG(
+          &urbg, absl::Span<uint32_t>(nullptr, 32)),
+      "!= nullptr");
+  (void)result;  // suppress unused-variable warning
+#endif
+}
+
+// The avalanche effect is a desirable cryptographic property of hashes in which
+// changing a single bit in the input causes each bit of the output to be
+// changed with probability near 50%.
+//
+// https://en.wikipedia.org/wiki/Avalanche_effect
+
+TEST(MixSequenceIntoSeedMaterial, AvalancheEffectTestOneBitLong) {
+  std::vector<uint32_t> seed_material = {1, 2, 3, 4, 5, 6, 7, 8};
+
+  // For every 32-bit number with exactly one bit set, verify the avalanche
+  // effect holds.  In order to reduce flakiness of tests, accept values
+  // anywhere in the range of 30%-70%.
+  for (uint32_t v = 1; v != 0; v <<= 1) {
+    std::vector<uint32_t> seed_material_copy = seed_material;
+    absl::random_internal::MixIntoSeedMaterial(
+        absl::Span<uint32_t>(&v, 1),
+        absl::Span<uint32_t>(seed_material_copy.data(),
+                             seed_material_copy.size()));
+
+    uint32_t changed_bits = 0;
+    for (size_t i = 0; i < seed_material.size(); i++) {
+      std::bitset<sizeof(uint32_t) * 8> bitset(seed_material[i] ^
+                                               seed_material_copy[i]);
+      changed_bits += bitset.count();
+    }
+
+    EXPECT_LE(changed_bits, 0.7 * sizeof(uint32_t) * 8 * seed_material.size());
+    EXPECT_GE(changed_bits, 0.3 * sizeof(uint32_t) * 8 * seed_material.size());
+  }
+}
+
+TEST(MixSequenceIntoSeedMaterial, AvalancheEffectTestOneBitShort) {
+  std::vector<uint32_t> seed_material = {1};
+
+  // For every 32-bit number with exactly one bit set, verify the avalanche
+  // effect holds.  In order to reduce flakiness of tests, accept values
+  // anywhere in the range of 30%-70%.
+  for (uint32_t v = 1; v != 0; v <<= 1) {
+    std::vector<uint32_t> seed_material_copy = seed_material;
+    absl::random_internal::MixIntoSeedMaterial(
+        absl::Span<uint32_t>(&v, 1),
+        absl::Span<uint32_t>(seed_material_copy.data(),
+                             seed_material_copy.size()));
+
+    uint32_t changed_bits = 0;
+    for (size_t i = 0; i < seed_material.size(); i++) {
+      std::bitset<sizeof(uint32_t) * 8> bitset(seed_material[i] ^
+                                               seed_material_copy[i]);
+      changed_bits += bitset.count();
+    }
+
+    EXPECT_LE(changed_bits, 0.7 * sizeof(uint32_t) * 8 * seed_material.size());
+    EXPECT_GE(changed_bits, 0.3 * sizeof(uint32_t) * 8 * seed_material.size());
+  }
+}
+
+}  // namespace