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* [Bug libstdc++/63176] New: std::generate_canonical<float, std::numeric_limits<float>::digits> generates 1.0
@ 2014-09-04 16:52 schwan@uni-mainz.de
2015-08-26 21:28 ` [Bug libstdc++/63176] std::generate_canonical<float, std::numeric_limits<float>::digits>() generates 1.0f redi at gcc dot gnu.org
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: schwan@uni-mainz.de @ 2014-09-04 16:52 UTC (permalink / raw)
To: gcc-bugs
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: schwan@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.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug libstdc++/63176] std::generate_canonical<float, std::numeric_limits<float>::digits>() generates 1.0f
2014-09-04 16:52 [Bug libstdc++/63176] New: std::generate_canonical<float, std::numeric_limits<float>::digits> generates 1.0 schwan@uni-mainz.de
@ 2015-08-26 21:28 ` redi at gcc dot gnu.org
2015-08-26 21:28 ` redi at gcc dot gnu.org
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: redi at gcc dot gnu.org @ 2015-08-26 21:28 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63176
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution|--- |FIXED
Target Milestone|--- |6.0
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Fixed on trunk.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug libstdc++/63176] std::generate_canonical<float, std::numeric_limits<float>::digits>() generates 1.0f
2014-09-04 16:52 [Bug libstdc++/63176] New: std::generate_canonical<float, std::numeric_limits<float>::digits> generates 1.0 schwan@uni-mainz.de
2015-08-26 21:28 ` [Bug libstdc++/63176] std::generate_canonical<float, std::numeric_limits<float>::digits>() generates 1.0f redi at gcc dot gnu.org
@ 2015-08-26 21:28 ` redi at gcc dot gnu.org
2015-10-10 3:45 ` rs2740 at gmail dot com
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: redi at gcc dot gnu.org @ 2015-08-26 21:28 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63176
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Author: redi
Date: Wed Aug 26 21:27:09 2015
New Revision: 227233
URL: https://gcc.gnu.org/viewcvs?rev=227233&root=gcc&view=rev
Log:
Ensure std::generate_canonical doesn't return 1.
2015-08-26 Edward Smith-Rowland <3dw4rd@verizon.net>
Jonathan Wakely <jwakely@redhat.com>
PR libstdc++/64351
PR libstdc++/63176
* include/bits/random.tcc (generate_canonical): Loop until we get a
result less than one.
* testsuite/26_numerics/random/uniform_real_distribution/operators/
64351.cc: New.
Added:
trunk/libstdc++-v3/testsuite/26_numerics/random/uniform_real_distribution/operators/64351.cc
Modified:
trunk/libstdc++-v3/ChangeLog
trunk/libstdc++-v3/include/bits/random.tcc
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug libstdc++/63176] std::generate_canonical<float, std::numeric_limits<float>::digits>() generates 1.0f
2014-09-04 16:52 [Bug libstdc++/63176] New: std::generate_canonical<float, std::numeric_limits<float>::digits> generates 1.0 schwan@uni-mainz.de
2015-08-26 21:28 ` [Bug libstdc++/63176] std::generate_canonical<float, std::numeric_limits<float>::digits>() generates 1.0f redi at gcc dot gnu.org
2015-08-26 21:28 ` redi at gcc dot gnu.org
@ 2015-10-10 3:45 ` rs2740 at gmail dot com
2015-10-12 10:28 ` redi at gcc dot gnu.org
2020-12-10 10:22 ` redi at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: rs2740 at gmail dot com @ 2015-10-10 3:45 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63176
TC <rs2740 at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |rs2740 at gmail dot com
--- Comment #3 from TC <rs2740 at gmail dot com> ---
This breaks the complexity requirement in [rand.util.canonical]/p3, though.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug libstdc++/63176] std::generate_canonical<float, std::numeric_limits<float>::digits>() generates 1.0f
2014-09-04 16:52 [Bug libstdc++/63176] New: std::generate_canonical<float, std::numeric_limits<float>::digits> generates 1.0 schwan@uni-mainz.de
` (2 preceding siblings ...)
2015-10-10 3:45 ` rs2740 at gmail dot com
@ 2015-10-12 10:28 ` redi at gcc dot gnu.org
2020-12-10 10:22 ` redi at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: redi at gcc dot gnu.org @ 2015-10-12 10:28 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63176
--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Meh. Don't use generate_canonical<float> then.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug libstdc++/63176] std::generate_canonical<float, std::numeric_limits<float>::digits>() generates 1.0f
2014-09-04 16:52 [Bug libstdc++/63176] New: std::generate_canonical<float, std::numeric_limits<float>::digits> generates 1.0 schwan@uni-mainz.de
` (3 preceding siblings ...)
2015-10-12 10:28 ` redi at gcc dot gnu.org
@ 2020-12-10 10:22 ` redi at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: redi at gcc dot gnu.org @ 2020-12-10 10:22 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63176
--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to TC from comment #3)
> This breaks the complexity requirement in [rand.util.canonical]/p3, though.
That did get fixed eventually, see PR 80137 / r246542
^ permalink raw reply [flat|nested] 6+ messages in thread
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2014-09-04 16:52 [Bug libstdc++/63176] New: std::generate_canonical<float, std::numeric_limits<float>::digits> generates 1.0 schwan@uni-mainz.de
2015-08-26 21:28 ` [Bug libstdc++/63176] std::generate_canonical<float, std::numeric_limits<float>::digits>() generates 1.0f redi at gcc dot gnu.org
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