logb, logbf, logbl, _logb, _logbf

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
);
#define logb(X) // Requires C11 or higher

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's 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, unless you're using the <tgmath.h> macro to call this function, logb always takes and returns a double.

If you use the logb macro from <tgmath.h>, the type of the argument determines which version of the function is selected. See Type-generic math for details.

By default, this function's global state is scoped to the application. To change this behavior, see Global state in the CRT.

Requirements

For more compatibility information, see Compatibility.

Libraries

All versions of the C run-time libraries.

See also

Math and floating-point support
frexp