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

NAME

     log, logf, log10, log10f, log1p, log1pf log2, log2f, -- logarithm functions

LIBRARY

     Math Library (libm, -lm)

SYNOPSIS

     #include <math.h>

     double
     log(double x);

     float
     logf(float x);

     double
     log10(double x);

     float
     log10f(float x);

     double
     log1p(double x);

     float
     log1pf(float x);

     double
     log2(double x);

     float
     log2f(float x);

DESCRIPTION

     The following functions compute logarithms:

       o   The log() and logf() functions return the natural logarithm.

       o   The log10() and log10f() functions return the base 10 logarithm.

       o   The log1p() and log1pf() functions return the natural logarithm of (1.0 + x) accurately even for very small values of x.

       o   The log2() and log2f() functions return the base 2 logarithm.

RETURN VALUES

     Upon successful completion, the functions return the logarithm of x as descibed above.  Otherwise the following may occur:

	   1.	If x is NaN, all functions return NaN.

	   2.	If x is positive infinity, all functions return x.  If x is negative infinity, all functions return NaN.

	   3.	If x is +0.0 or -0.0, the log(), log10(), and log2() families return either -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL, whereas the
		log1p() family returns x.

	   4.	If x is +1.0, the log(), log10(), and log2() families return +0.0.  If x is -1.0, the log1p() family returns -HUGE_VAL,
		-HUGE_VALF, or -HUGE_VALL.

     In addition, on a VAX, errno is set to EDOM and the reserved operand is returned by log() unless x > 0, by log1p() unless x > -1.

SEE ALSO

     exp(3), ilogb(3), math(3)

STANDARDS

     The described functions conform to ISO/IEC 9899:1999 (``ISO C99'').

HISTORY

     The history of the logarithm functions dates back to Version 6 AT&T UNIX.

BSD
								September 13, 2011							       BSD