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-exception
6//
7//===----------------------------------------------------------------------===//
8
9#ifndef LLVM_LIBC_SRC___SUPPORT_HASHTABLE_RANDOMNESS_H
10#define LLVM_LIBC_SRC___SUPPORT_HASHTABLE_RANDOMNESS_H
11
12#include "src/__support/common.h"
13#include "src/__support/hash.h"
14#include "src/__support/macros/attributes.h"
15#if defined(LIBC_HASHTABLE_USE_GETRANDOM)
16#include "src/errno/libc_errno.h"
17#include "src/sys/random/getrandom.h"
18#endif
19
20namespace LIBC_NAMESPACE {
21namespace internal {
22namespace randomness {
23// We need an initial state for the hash function. More entropy are to be added
24// at the first use and each round of reseeding. The following random numbers
25// are generated from https://www.random.org/cgi-bin/randbyte?nbytes=64&format=h
26LIBC_INLINE_VAR thread_local HashState state = {
27 0x38049a7ea6f5a79b, 0x45cb02147c3f718a, 0x53eb431c12770718,
28 0x5b55742bd20a2fcb};
29LIBC_INLINE_VAR thread_local uint64_t counter = 0;
30LIBC_INLINE_VAR constexpr uint64_t RESEED_PERIOD = 1024;
31LIBC_INLINE uint64_t next_random_seed() {
32 if (counter % RESEED_PERIOD == 0) {
33 uint64_t entropy[2];
34 entropy[0] = reinterpret_cast<uint64_t>(&entropy);
35 entropy[1] = reinterpret_cast<uint64_t>(&state);
36#if defined(LIBC_HASHTABLE_USE_GETRANDOM)
37 int errno_backup = libc_errno;
38 ssize_t count = sizeof(entropy);
39 uint8_t *buffer = reinterpret_cast<uint8_t *>(entropy);
40 while (count > 0) {
41 ssize_t len = getrandom(buffer, count, 0);
42 if (len == -1) {
43 if (libc_errno == ENOSYS)
44 break;
45 continue;
46 }
47 count -= len;
48 buffer += len;
49 }
50 libc_errno = errno_backup;
51#endif
52 state.update(ptr: &entropy, size: sizeof(entropy));
53 }
54 state.update(ptr: &counter, size: sizeof(counter));
55 counter++;
56 return state.finish();
57}
58
59} // namespace randomness
60} // namespace internal
61} // namespace LIBC_NAMESPACE
62#endif // LLVM_LIBC_SRC___SUPPORT_HASHTABLE_RANDOMNESS_H
63

source code of libc/src/__support/HashTable/randomness.h