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https://issues.apache.org/jira/browse/STDCXX-51?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12600157#action_12600157
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Farid Zaripov commented on STDCXX-51:
-------------------------------------
From: http://developer.intel.com/design/pentium/manuals/24319001.pdf
As a general rule, when a QNaN is used in one or more arithmetic floating-point
instructions, it
is allowed to propagate through a computation. An SNaN on the other hand causes
a floatingpoint
invalid-operation exception to be signaled. SNaNs are typically used to trap or
invoke an
exception handler. They must be inserted by software; that is, *the* *FPU*
*never* *generates* *an* *SNaN*
*as* *a* *result*.
The floating-point invalid-operation exception has a flag and a mask bit
associated with it in the
FPU status and control registers, respectively (see Section 7.7.,
"Floating-Point Exception
Handling"). The mask bit determines how the FPU handles an SNaN value. *If*
*the* *floating-point*
*invalid-operation* *mask* *bit* *is* *set,* *the* *SNaN* *is* *converted* *to*
*a* *QNaN* *by* *setting* *the* *most-significant*
*fraction* *bit* *of* *the* *value* *to* *1.* The result is then stored in the
destination operand and the
floating-point invalid-operation flag is set. If the invalid-operation mask is
clear, a floating-point
invalid-operation fault is signaled and no result is stored in the destination
operand.
> infinity, NaN formatted differently on different platforms
> ----------------------------------------------------------
>
> Key: STDCXX-51
> URL: https://issues.apache.org/jira/browse/STDCXX-51
> Project: C++ Standard Library
> Issue Type: Improvement
> Components: 22. Localization
> Affects Versions: 4.1.2, 4.1.3, 4.1.4, 4.2.0, 4.2.1
> Environment: all
> Reporter: Martin Sebor
> Assignee: Martin Sebor
> Priority: Minor
> Fix For: 4.2.2
>
> Attachments: num_put.diff
>
> Original Estimate: 13h
> Time Spent: 13h
> Remaining Estimate: 8h
>
> The output of the program below is different depending on the operating
> system it runs on. It should be the same (preferably like that on AIX).
> {noformat}
> $ cat u.cpp && uname -sr && make u -r && ./u
> #include <iostream>
> #include <limits>
> int main ()
> {
> std::cout << std::numeric_limits<double>::infinity () << '\n'
> << std::numeric_limits<double>::quiet_NaN () << '\n'
> << std::numeric_limits<double>::signaling_NaN () << '\n';
> }
> SunOS 5.9
> gcc -c -I/build/sebor/dev/stdlib/include/ansi -D_RWSTDDEBUG -pthreads
> -D_RWSTD_USE_CONFIG -I/build/sebor/gcc-3.4.3-15s/include
> -I/build/sebor/dev/stdlib/include -I/build/sebor/dev/stdlib/examples/include
> -pedantic -nostdinc++ -g -Wall -W -Wcast-qual -Winline -Wshadow
> -Wwrite-strings -Wno-long-long u.cpp
> gcc u.o -o u -pthreads -L/build/sebor/gcc-3.4.3-15s/lib -lstd15s -lsupc++ -lm
> rm u.o
> inf
> nan
> nan
> $ uname -vs && gmake u -r && ./u
> AIX 5
> xlCcore_r -c -I/build/sebor/dev/stdlib/include/ansi -D_RWSTDDEBUG
> -D_RWSTD_USE_CONFIG -I/build/sebor/vacpp-7.0.0.3-15D/include
> -I/build/sebor/dev/stdlib/include -I/build/sebor/dev/stdlib/examples/include
> -g -q64 -qtemplateregistry=u.ti u.cpp
> xlCcore_r u.o -o u -I/build/sebor/dev/stdlib/include/ansi -D_RWSTDDEBUG
> -D_RWSTD_USE_CONFIG -liconv -brtl -q64
> -I/build/sebor/dev/stdlib/include/ansi -D_RWSTDDEBUG -D_RWSTD_USE_CONFIG
> -I/build/sebor/vacpp-7.0.0.3-15D/include -I/build/sebor/dev/stdlib/include
> -I/build/sebor/dev/stdlib/examples/include -qtemplateregistry=u.ti
> -L/build/sebor/vacpp-7.0.0.3-15D/lib -lstd15D -lm
> rm u.o
> inf
> nanq
> nans
> {noformat}
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