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| author | Joseph Huber <35342157+jhuber6@users.noreply.github.com> | 2023-09-12 16:52:20 -0500 |
|---|---|---|
| committer | GitHub <noreply@github.com> | 2023-09-12 16:52:20 -0500 |
| commit | ef169f5707075e6f59f2add26333f56376b5ac64 (patch) | |
| tree | 5f0543627856077c81c8eed2b306a88797c22113 /libc/src/stdlib/rand_util.cpp | |
| parent | d671126ad097ffd1bb19322005902676945862c2 (diff) | |
| download | llvm-ef169f5707075e6f59f2add26333f56376b5ac64.zip llvm-ef169f5707075e6f59f2add26333f56376b5ac64.tar.gz llvm-ef169f5707075e6f59f2add26333f56376b5ac64.tar.bz2 | |
[libc] Improve the implementation of the rand() function (#66131)
Summary:
This patch improves the implementation of the standard `rand()` function
by implementing it in terms of the xorshift64star pRNG as described in
https://en.wikipedia.org/wiki/Xorshift#xorshift*. This is a good,
general purpose random number generator that is sufficient for most
applications that do not require an extremely long period. This patch
also correctly initializes the seed to be `1` as described by the
standard. We also increase the `RAND_MAX` value to be `INT_MAX` as the
standard only specifies that it can be larger than 32768.
Diffstat (limited to 'libc/src/stdlib/rand_util.cpp')
| -rw-r--r-- | libc/src/stdlib/rand_util.cpp | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/libc/src/stdlib/rand_util.cpp b/libc/src/stdlib/rand_util.cpp index 9c29eb8..dac8dca 100644 --- a/libc/src/stdlib/rand_util.cpp +++ b/libc/src/stdlib/rand_util.cpp @@ -11,6 +11,8 @@ namespace __llvm_libc { -LIBC_THREAD_LOCAL unsigned long rand_next; +// C standard 7.10p2: If 'rand' is called before 'srand' it is to proceed as if +// the 'srand' function was called with a value of '1'. +LIBC_THREAD_LOCAL unsigned long rand_next = 1; } // namespace __llvm_libc |