Article: Q119458
Product(s): Microsoft C Compiler
Version(s): winnt:
Operating System(s):
Keyword(s): kbCRT kbVC
Last Modified: 29-JUL-2001
-------------------------------------------------------------------------------
The information in this article applies to:
- The C Run-Time (CRT), included with:
- Microsoft Visual C++, versions 1.0, 1.50
- *EDITOR Please do not choose this product*Microsoft Visual C++ 32-bit Edition* use 241, 265, 225, versions 1.0, 2.0, 2.1
-------------------------------------------------------------------------------
SUMMARY
=======
Calling _fpreset() reinitializes the floating-point math package. The header
file FLOAT.H contains the following definition of _CW_DEFAULT:
/* initial Control Word value */
#ifdef _M_IX86
#define _CW_DEFAULT ( _RC_NEAR + _PC_64 + _EM_INVALID + _EM_ZERODIVIDE +
_EM_OVERFLOW + _EM_UNDERFLOW + _EM_INEXACT )
#endif
You might expect that if you call _fpreset() and then call _controlfp(0,0) to get
the control word, that the control word will be _CW_DEFAULT; however, that is
not the case. _CW_DEFAULT does not actually correspond to the default value of
the x87 control word. The difference is that _CW_DEFAULT does not mask the
denormal exception. The _fpreset() routine masks all exceptions, including
denormal.
The denormal exception does not belong to the set of floating-point exceptions
specified by the IEEE Standard. You cannot mask or unmask the exception using
_controlfp(). The abstract control word used by the C run- time reserves the
upper bits for machine-specific features. Therefore, you should not compare full
control-word encodings; instead, you should compare the bits that you are
interested in.
Additional query words: kbinf 1.00 1.50 2.00 2.10
======================================================================
Keywords : kbCRT kbVC
Technology : kbVCsearch kbAudDeveloper kbCRT
Version : winnt:
=============================================================================