log2

log2

Compute the logarithm base 2

Portability: C99

SYNOPSIS
DESCRIPTION
RETURN VALUE
DIAGNOSTICS
RELATED FUNCTIONS
SEE ALSO

SYNOPSIS

   #include <math.h>

   double log2(double x);
   float log2f(float x);
   long double log2l(long double x);

DESCRIPTION

log2 computes the binary (base 2) logarithm of its argument x. x must be greater than zero.

The function name log2f should be used for float arguments, and log2l for long double arguments. Alternately, if the header file tgmath.h is included, log2 may be used with any numeric argument type.

RETURN VALUE

log2 returns the binary (base 2) logarithm of its argument, provided this value is defined and expressible.

DIAGNOSTICS

If the argument of log2 is invalid, it returns -HUGE_VAL in hexadecimal floating point, or a NaN in binary floating point. In this case, the run-time library writes an error message to the standard error file stderr. log2(0.0) returns negative infinity in binary floating point.

If an error occurs in log2, the _matherr or _matherb routine is called. You can supply your own version of _matherr or _matherb to suppress the diagnostic message or modify the value returned.

RELATED FUNCTIONS

exp2, log, _matherb, _matherr

SEE ALSO

"Mathematical Functions" in Chapter 2, "Function Categories"

Chapter Contents
Previous
Next
Top of Page