| 1 | //===-- Implementation of rand --------------------------------------------===// |
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| 2 | // |
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| 3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
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| 4 | // See https://llvm.org/LICENSE.txt for license information. |
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| 5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
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| 6 | // |
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| 7 | //===----------------------------------------------------------------------===// |
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| 8 | |
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| 9 | #include "src/stdlib/rand.h" |
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| 10 | #include "src/__support/common.h" |
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| 11 | #include "src/__support/macros/config.h" |
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| 12 | #include "src/__support/threads/sleep.h" |
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| 13 | #include "src/stdlib/rand_util.h" |
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| 14 | |
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| 15 | namespace LIBC_NAMESPACE_DECL { |
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| 16 | |
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| 17 | LLVM_LIBC_FUNCTION(int, rand, (void)) { |
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| 18 | unsigned long orig = rand_next.load(cpp::MemoryOrder::RELAXED); |
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| 19 | |
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| 20 | // An implementation of the xorshift64star pseudo random number generator. |
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| 21 | // This is a good general purpose generator for most non-cryptographics |
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| 22 | // applications. |
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| 23 | if constexpr (sizeof(void *) == sizeof(uint64_t)) { |
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| 24 | for (;;) { |
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| 25 | unsigned long x = orig; |
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| 26 | x ^= x >> 12; |
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| 27 | x ^= x << 25; |
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| 28 | x ^= x >> 27; |
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| 29 | if (rand_next.compare_exchange_strong(orig, x, cpp::MemoryOrder::ACQUIRE, |
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| 30 | cpp::MemoryOrder::RELAXED)) |
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| 31 | return static_cast<int>((x * 0x2545F4914F6CDD1Dul) >> 32) & RAND_MAX; |
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| 32 | sleep_briefly(); |
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| 33 | } |
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| 34 | } else { |
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| 35 | // This is the xorshift32 pseudo random number generator, slightly different |
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| 36 | // from the 64-bit star version above, as the previous version fails to |
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| 37 | // generate uniform enough LSB in 32-bit systems. |
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| 38 | for (;;) { |
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| 39 | unsigned long x = orig; |
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| 40 | x ^= x >> 13; |
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| 41 | x ^= x << 27; |
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| 42 | x ^= x >> 5; |
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| 43 | if (rand_next.compare_exchange_strong(orig, x, cpp::MemoryOrder::ACQUIRE, |
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| 44 | cpp::MemoryOrder::RELAXED)) |
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| 45 | return static_cast<int>(x * 1597334677ul) & RAND_MAX; |
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| 46 | sleep_briefly(); |
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| 47 | } |
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| 48 | } |
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| 49 | __builtin_unreachable(); |
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| 50 | } |
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| 51 | |
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| 52 | } // namespace LIBC_NAMESPACE_DECL |
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| 53 | |
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