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Add test for integer hash quality.

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Change-Id: I8de0f11c0a7d21d980f5d8691a6e3888a386cbba
Reviewed-on: https://chromium-review.googlesource.com/c/1386144
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58400}
This commit is contained in:
Yang Guo 2018-12-20 09:37:19 +01:00 committed by Commit Bot
parent b3c85c9e26
commit 3b02afc538
1 changed files with 44 additions and 0 deletions
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44
test/cctest/test-hashcode.cc
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@ -227,5 +227,49 @@ TEST(TransitionSlowToFastWithPropertyArray) {
CheckFastObject(obj, hash);
}
void TestIntegerHashQuality(const int samples_log2, int num_buckets_log2,
uint64_t seed, double max_var) {
int samples = 1 << samples_log2;
int num_buckets = 1 << num_buckets_log2;
int mean = samples / num_buckets;
int* buckets = new int[num_buckets];
for (int i = 0; i < num_buckets; i++) buckets[i] = 0;
for (int i = 0; i < samples; i++) {
uint32_t hash = ComputeSeededHash(i, seed);
buckets[hash % num_buckets]++;
}
int sum_deviation = 0;
for (int i = 0; i < num_buckets; i++) {
int deviation = abs(buckets[i] - mean);
sum_deviation += deviation * deviation;
}
delete[] buckets;
double variation_coefficient = sqrt(sum_deviation * 1.0 / num_buckets) / mean;
printf("samples: 1 << %2d, buckets: 1 << %2d, var_coeff: %0.3f\n",
samples_log2, num_buckets_log2, variation_coefficient);
CHECK_LT(variation_coefficient, max_var);
}
TEST(IntegerHashQuality) {
TestIntegerHashQuality(17, 13, 0x123456789ABCDEFU, 0.4);
TestIntegerHashQuality(16, 12, 0x123456789ABCDEFU, 0.4);
TestIntegerHashQuality(15, 11, 0xFEDCBA987654321U, 0.4);
TestIntegerHashQuality(14, 10, 0xFEDCBA987654321U, 0.4);
TestIntegerHashQuality(13, 9, 1, 0.4);
TestIntegerHashQuality(12, 8, 1, 0.4);
TestIntegerHashQuality(17, 10, 0x123456789ABCDEFU, 0.2);
TestIntegerHashQuality(16, 9, 0x123456789ABCDEFU, 0.2);
TestIntegerHashQuality(15, 8, 0xFEDCBA987654321U, 0.2);
TestIntegerHashQuality(14, 7, 0xFEDCBA987654321U, 0.2);
TestIntegerHashQuality(13, 6, 1, 0.2);
TestIntegerHashQuality(12, 5, 1, 0.2);
}
} // namespace internal
} // namespace v8