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1//===-- HashTable Randomness ------------------------------------*- C++ -*-===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8 9#ifndef LLVM_LIBC_SRC___SUPPORT_HASHTABLE_RANDOMNESS_H10#define LLVM_LIBC_SRC___SUPPORT_HASHTABLE_RANDOMNESS_H11 12#include "src/__support/common.h"13#include "src/__support/hash.h"14#include "src/__support/macros/attributes.h"15#include "src/__support/macros/config.h"16#if defined(LIBC_HASHTABLE_USE_GETRANDOM)17#include "hdr/errno_macros.h"18#include "src/__support/OSUtil/linux/getrandom.h"19#endif20 21namespace LIBC_NAMESPACE_DECL {22namespace internal {23namespace randomness {24// We need an initial state for the hash function. More entropy are to be added25// at the first use and each round of reseeding. The following random numbers26// are generated from https://www.random.org/cgi-bin/randbyte?nbytes=64&format=h27LIBC_INLINE_VAR thread_local HashState state = {28 0x38049a7ea6f5a79b, 0x45cb02147c3f718a, 0x53eb431c12770718,29 0x5b55742bd20a2fcb};30LIBC_INLINE_VAR thread_local uint64_t counter = 0;31LIBC_INLINE_VAR constexpr uint64_t RESEED_PERIOD = 1024;32LIBC_INLINE uint64_t next_random_seed() {33 if (counter % RESEED_PERIOD == 0) {34 uint64_t entropy[2];35 entropy[0] = reinterpret_cast<uint64_t>(&entropy);36 entropy[1] = reinterpret_cast<uint64_t>(&state);37#if defined(LIBC_HASHTABLE_USE_GETRANDOM)38 size_t count = sizeof(entropy);39 uint8_t *buffer = reinterpret_cast<uint8_t *>(entropy);40 while (count > 0) {41 auto len = internal::getrandom(buffer, count, 0);42 if (!len.has_value()) {43 if (len.error() == ENOSYS)44 break;45 continue;46 }47 count -= len.value();48 buffer += len.value();49 }50#endif51 state.update(&entropy, sizeof(entropy));52 }53 state.update(&counter, sizeof(counter));54 counter++;55 return state.finish();56}57 58} // namespace randomness59} // namespace internal60} // namespace LIBC_NAMESPACE_DECL61#endif // LLVM_LIBC_SRC___SUPPORT_HASHTABLE_RANDOMNESS_H62