std::uniform_int_distribution erroneously rejects generator values #38557
Description
| Bugzilla Link | 39209 |
| Version | 6.0 |
| OS | All |
| Attachments | Demonstration of bug |
| Reporter | LLVM Bugzilla Contributor |
| CC | @mclow |
Extended Description
Given a generator returning values in the interval [0, r] and std::uniform_int_distribution(0, b), let r,b such that r+1 multiple of b+1. In this case std::uniform_int_distribution may erroneously reject generator values although no rejection sampling is needed.
In the demonstration program in the attachment, r=19, b=9 so that half of all generator values are rejected. The bug does not occur if r+1 and b+1 are powers of two.
Note that the GNU C++ Library contains a similar bug:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80977
$ clang++ --version
clang version 6.0.1 (tags/RELEASE_601/final)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/lib/llvm/6/bin