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logb, logbf, logbl, _logb, _logbf

 

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Extracts the exponent value of a floating-point argument.

Syntax

double logb(  
   double x   
);  
float logb(  
   float x   
); // C++ only  
long double logb(  
   long double x   
); // C++ only   
float logbf(  
   float x   
);  
long double logbl(  
   long double x   
);  
double _logb(  
   double x   
);  
float _logbf(  
   float x   
);  

Parameters

x
A floating-point value.

Return Value

logb returns the unbiased exponent value of x as a signed integer represented as a floating-point value.

Remarks

The logb functions extract the exponential value of the 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.

Because C++ allows overloading, you can call overloads of logb that take and return float or long double values. In a C program, logb always takes and returns a double.

Input SEH exception Matherr exception
± QNAN,IND None _DOMAIN
± 0 ZERODIVIDE _SING

Requirements

Routine Required header
_logb <float.h>
logb, logbf, logbl, _logbf <math.h>

For more compatibility information, see Compatibility.

Libraries

All versions of the C run-time libraries.

.NET Framework Equivalent

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

See Also

Floating-Point Support
frexp