freebsd man page for log2

LOG(3)							   BSD Library Functions Manual 						    LOG(3)

NAME
     log, logf, logl, log10, log10f, log10l, log2, log2f, log2l, log1p, log1pf, log1pl -- logarithm functions

LIBRARY
     Math Library (libm, -lm)

SYNOPSIS
     #include <math.h>

     double
     log(double x);

     float
     logf(float x);

     long double
     logl(long double x);

     double
     log10(double x);

     float
     log10f(float x);

     long double
     log10l(long double x);

     double
     log2(double x);

     float
     log2f(float x);

     long double
     log2l(long double x);

     double
     log1p(double x);

     float
     log1pf(float x);

     long double
     log1pl(long double x);

DESCRIPTION
     The log(), logf(), and logl() functions compute the natural logarithm of x.

     The log10(), log10f(), and log10l() functions compute the logarithm base 10 of x, while log2(), log2f(), and log2l() compute the logarithm
     base 2 of x.

     The log1p(), log1pf(), and log1pl() functions compute the natural logarithm of 1 + x.  Computing the natural logarithm as log1p(x) is more
     accurate than computing it as log(1 + x) when x is close to zero.

RETURN VALUES
     These functions return the requested logarithm; the logarithm of 1 is +0.	An attempt to take the logarithm of +-0 results in a divide-by-
     zero exception, and -infinity is returned.  Otherwise, attempting to take the logarithm of a negative number results in an invalid exception
     and a return value of NaN.

SEE ALSO
     exp(3), ilogb(3), math(3), pow(3)

STANDARDS
     The log(), logf(), logl(), log10(), log10f(), log10l(), log2(), log2f(), log2l(), log1p(), log1pf(), and log1pl() functions conform to
     ISO/IEC 9899:1999 (``ISO C99'').

BSD
								   June 3, 2013 							       BSD