llvm/libc/test/src/__support/hash_test.cpp

//===-- Unittests for hash ------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#include "src/__support/CPP/new.h"
#include "src/__support/hash.h"
#include "src/stdlib/rand.h"
#include "src/stdlib/srand.h"
#include "src/string/memset.h"
#include "test/UnitTest/Test.h"

template <class T> struct AlignedMemory { … };

size_t sizes[] = …;
uint8_t values[] = …;

// Hash value should not change with different alignments.
TEST(LlvmLibcHashTest, SanityCheck) { … }

static inline size_t popcnt(uint64_t x) { … }

// Mutate a single bit in a rather large input. The hash should change
// significantly. At least one fifth of the bits should not match.
TEST(LlvmLibcHashTest, Avalanche) { … }

// Hash a random sequence of input. The LSB should be uniform enough such that
// values spread across the entire range.
TEST(LlvmLibcHashTest, UniformLSB) { … }

// Hash a low entropy sequence. The MSB should be uniform enough such that
// there is no significant bias even if the value range is small.
// Top 7 bits is examined because it will be used as a secondary key in
// the hash table.
TEST(LlvmLibcHashTest, UniformMSB) { … }