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 #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 #endif 20 21 namespace LIBC_NAMESPACE_DECL { 22 namespace internal { 23 namespace randomness { 24 // We need an initial state for the hash function. More entropy are to be added 25 // at the first use and each round of reseeding. The following random numbers 26 // are generated from https://www.random.org/cgi-bin/randbyte?nbytes=64&format=h 27 LIBC_INLINE_VAR thread_local HashState state = { 28 0x38049a7ea6f5a79b, 0x45cb02147c3f718a, 0x53eb431c12770718, 29 0x5b55742bd20a2fcb}; 30 LIBC_INLINE_VAR thread_local uint64_t counter = 0; 31 LIBC_INLINE_VAR constexpr uint64_t RESEED_PERIOD = 1024; next_random_seed()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 #endif 51 state.update(&entropy, sizeof(entropy)); 52 } 53 state.update(&counter, sizeof(counter)); 54 counter++; 55 return state.finish(); 56 } 57 58 } // namespace randomness 59 } // namespace internal 60 } // namespace LIBC_NAMESPACE_DECL 61 #endif // LLVM_LIBC_SRC___SUPPORT_HASHTABLE_RANDOMNESS_H 62