https://llvm.org/bugs/show_bug.cgi?id=26395
Bug ID: 26395
Summary: Analyzer says undefined behavior in
uniform_int_distribution<size_t>
Product: libc++
Version: 3.7
Hardware: Macintosh
OS: MacOS X
Status: NEW
Severity: normal
Priority: P
Component: All Bugs
Assignee: unassignedclangb...@nondot.org
Reporter: jared.gr...@gmail.com
CC: llvm-bugs@lists.llvm.org, mclow.li...@gmail.com
Classification: Unclassified
The clang static analyzer flags this code as having undefined behavior. Note
that if I change "size_t" to "unsigned" then things look fine. It looks like
the engine is 32-bit but it's going to try a 64-bit shift maybe? I'm totally
guessing here.
.../c++/v1/algorithm:2920
warning: The result of the '>>' expression is undefined
__mask0_ = __w0_ > 0 ? _Engine_result_type(~0) >> (_EDt - __w0_) :
~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
To reproduce:
$ cat x.cpp
#include <random>
#include <cstddef>
size_t genRandom(size_t maxValue) {
std::minstd_rand engine;
std::uniform_int_distribution<size_t> dist{0, maxValue};
return dist(engine);
}
$ clang++ x.cpp -std=c++14 --analyze
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