1 //===-- Implementation of rand --------------------------------------------===// 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 #include "src/stdlib/rand.h" 10 #include "src/__support/common.h" 11 #include "src/__support/threads/sleep.h" 12 #include "src/stdlib/rand_util.h" 13 14 namespace LIBC_NAMESPACE { 15 16 // An implementation of the xorshift64star pseudo random number generator. This 17 // is a good general purpose generator for most non-cryptographics applications. 18 LLVM_LIBC_FUNCTION(int, rand, (void)) { 19 unsigned long orig = rand_next.load(cpp::MemoryOrder::RELAXED); 20 for (;;) { 21 unsigned long x = orig; 22 x ^= x >> 12; 23 x ^= x << 25; 24 x ^= x >> 27; 25 if (rand_next.compare_exchange_strong(orig, x, cpp::MemoryOrder::ACQUIRE, 26 cpp::MemoryOrder::RELAXED)) 27 return static_cast<int>((x * 0x2545F4914F6CDD1Dul) >> 32) & RAND_MAX; 28 sleep_briefly(); 29 } 30 } 31 32 } // namespace LIBC_NAMESPACE 33