https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63176
Bug ID: 63176
Summary: std::generate_canonical<float,
std::numeric_limits<float>::digits> generates 1.0
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: sch...@uni-mainz.de
std::generate_canonical can generate 1.0, which does not conform to the c++11
standard. On my box the following program yields "Bug!":
#include <iostream>
#include <limits>
#include <random>
int main()
{
std::mt19937 rng;
std::seed_seq sequence{0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
rng.seed(sequence);
rng.discard(12 * 629143 + 6);
float random = std::generate_canonical<float,
std::numeric_limits<float>::digits>(rng);
if (random == 1.0f)
{
std::cout << "Bug!\n";
}
return 0;
}
See also
http://stackoverflow.com/questions/25668600/is-1-0-a-valid-random-number for a
longer discussion and analysis of the problem.
I first noticed this on my system GCC,
gcc (Gentoo 4.7.3-r1 p1.4, pie-0.5.5) 4.7.3
Copyright (C) 2012 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
but I can reproduce the same behavior with a recent GCC from git:
gcc (GCC) 5.0.0 20140830 (experimental)
Copyright (C) 2014 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
I used `c++ =std=c++11` to compile the program above.
