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

NAME
       log, logf, logl - natural logarithm function

SYNOPSIS
       c99 [ 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,
       log(e)(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 float‐
		       ing-point exception is raised.

USAGE
       An application wanting to check for exceptions should  call  feclearex‐
       cept(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 5.11			  12 Jul 2006			       log(3M)
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