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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) accu-
	   rately 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.  Oth-
     erwise 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
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