log(3M) 						  Mathematical Library Functions						   log(3M)

NAME

       log, logf, logl - natural logarithm function

SYNOPSIS

       cc [ flag... ] file... -lm [ library... ]
       #include <math.h>

       double log(double x);

       float logf(float x);

       long double logl(long double x);

DESCRIPTION

       These functions compute the natural logarithm of their argument x, loge(x).

RETURN VALUES

       Upon successful completion, log() returns the natural logarithm of x.

       If x is +-0, a pole error occurs and log(), logf(), and logl() return -HUGE_VAL, -HUGE_VALF, and -HUGE_VALL, respectively.

       For finite values of x that are less than 0, or if x is -Inf, a domain error occurs and a NaN is returned.

       If x is NaN, a NaN is returned.

       If x is 1, +0 is returned.

       If x is +Inf, x is returned.

       For exceptional cases, matherr(3M) tabulates the values to be returned by log() as specified by SVID3 and XPG3.

ERRORS

       These functions will fail if:

       Domain Error    The finite value of x is negative, or x is -Inf.

		       If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, the invalid floating-point exception is raised.

		       The log() function sets errno to EDOM if the value of x is negative.

       Pole Error      The value of x is 0.

		       If  the	integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, the divide-by-zero floating-point exception is
		       raised.

USAGE

       An application wanting to check for exceptions should call feclearexcept(FE_ALL_EXCEPT) before  calling	these  functions.  On  return,	if
       fetestexcept(FE_INVALID	|  FE_DIVBYZERO  |  FE_OVERFLOW  |  FE_UNDERFLOW) is non-zero, an exception has been raised. An application should
       either examine the return value or check the floating point exception flags to detect exceptions.

       An application can also set errno to 0 before calling log(). On return, if errno is non-zero, an error has occurred. The logf() and  logl()
       functions do not set errno.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |MT-Safe			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       exp(3M), feclearexcept(3M), fetestexcept(3M), isnan(3M), log10(3M), log1p(3M), math.h(3HEAD), matherr(3M), attributes(5), standards(5)

SunOS 5.10							    1 Sep 2002								   log(3M)