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* Re: libstdc++/9151: [3.2/3.3/3.4 regression] std::setprecision limited to 16 digits when outputting a double to a stream
@ 2003-01-06 11:03 paolo
0 siblings, 0 replies; 3+ messages in thread
From: paolo @ 2003-01-06 11:03 UTC (permalink / raw)
To: andrew, gcc-bugs, gcc-prs, nobody, paolo
Synopsis: [3.2/3.3/3.4 regression] std::setprecision limited to 16 digits when outputting a double to a stream
Responsible-Changed-From-To: unassigned->paolo
Responsible-Changed-By: paolo
Responsible-Changed-When: Mon Jan 6 03:03:13 2003
Responsible-Changed-Why:
Working on it.
State-Changed-From-To: open->analyzed
State-Changed-By: paolo
State-Changed-When: Mon Jan 6 03:03:13 2003
State-Changed-Why:
Confirmed.
http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=9151
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: libstdc++/9151: [3.2/3.3/3.4 regression] std::setprecision limited to 16 digits when outputting a double to a stream
@ 2003-01-06 15:53 paolo
0 siblings, 0 replies; 3+ messages in thread
From: paolo @ 2003-01-06 15:53 UTC (permalink / raw)
To: andrew, gcc-bugs, gcc-prs, paolo
Synopsis: [3.2/3.3/3.4 regression] std::setprecision limited to 16 digits when outputting a double to a stream
State-Changed-From-To: analyzed->closed
State-Changed-By: paolo
State-Changed-When: Mon Jan 6 07:53:47 2003
State-Changed-Why:
Fixed for 3.2.2 and 3.3.
http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=9151
^ permalink raw reply [flat|nested] 3+ messages in thread
* libstdc++/9151: [3.2/3.3/3.4 regression] std::setprecision limited to 16 digits when outputting a double to a stream
@ 2003-01-03 6:16 andrew
0 siblings, 0 replies; 3+ messages in thread
From: andrew @ 2003-01-03 6:16 UTC (permalink / raw)
To: gcc-gnats
>Number: 9151
>Category: libstdc++
>Synopsis: [3.2/3.3/3.4 regression] std::setprecision limited to 16 digits when outputting a double to a stream
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: unassigned
>State: open
>Class: sw-bug
>Submitter-Id: net
>Arrival-Date: Thu Jan 02 22:16:01 PST 2003
>Closed-Date:
>Last-Modified:
>Originator: Andrew Pollard
>Release: gcc-3.2 and above
>Organization:
>Environment:
i686-pc-linux-gnu on a PIII system
>Description:
[ Re: http://gcc.gnu.org/ml/libstdc++/2002-12/msg00064.html ]
libstdc++-v3 in gcc-3.2 and above limits the precision in a std::setprecision() call to 16 digits when outputting a double to a stream. This (for some reason) causes the output of std::numeric_limits<double>::min() to be such that when you read the string value back into a double, the double is not the same as the double output.
For some reason double::min() requires 18 digits for this to
work.
A test case follows...
double.c:
----------------------------
#include <limits>
#include <sstream>
#include <iomanip>
int
main()
{
int prec = std::numeric_limits<double>::digits10+3;
double val1 = std::numeric_limits<double>::min();
double val2 = 0.0;
std::stringstream ss1;
ss1 << std::setprecision(prec) << val1 << std::ends;
std::stringstream ss2(ss1.str());
ss2 >> val2;
return (val1 == val2);
}
--------------------------------
% g++30 double.cxx; ./a.out; echo $?
1
% g++32 double.cxx; ./a.out; echo $?
0
% g++33 double.cxx; ./a.out; echo $?
0
% g++34 double.cxx; ./a.out; echo $?
0
>How-To-Repeat:
>Fix:
The 'obvious fix' is to change the +1 to a +3 in include/bits/locale_facets.tcc:_M_convert_float line 627
[seems to be the same code in 3.2/3.3 and 3.4]
Quite why this needs 18 digits here, I haven't got a clue though.
>Release-Note:
>Audit-Trail:
>Unformatted:
^ permalink raw reply [flat|nested] 3+ messages in thread
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2003-01-06 11:03 libstdc++/9151: [3.2/3.3/3.4 regression] std::setprecision limited to 16 digits when outputting a double to a stream paolo
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2003-01-06 15:53 paolo
2003-01-03 6:16 andrew
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