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Extracts an exponential value of a double-precision floating-point argument.

double _logb(
   double x 



Double-precision floating-point value.

_logb returns the unbiased exponential value of x.

The _logb function extracts the exponential value of its double-precision floating-point argument x, as though x were represented with infinite range. If the argument x is denormalized, it is treated as if it were normalized.

Input SEH exception Matherr exception




± 0



Routine Required header Compatibility



ANSI, Windows 95, Windows 98, Windows 98 Second Edition, Windows Millennium Edition, Windows Millennium Edition, Windows NT 4.0, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003

For more compatibility information, see Compatibility in the Introduction.


All versions of the C run-time libraries.

Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.