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LOG1P(3)                   Linux Programmer's Manual                  LOG1P(3)



NAME
       log1p, log1pf, log1pl -  logarithm of 1 plus argument

SYNOPSIS
       #include <math.h>

       double log1p(double x);
       float log1pf(float x);
       long double log1pl(long double x);

       Link with -lm.

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       log1p(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 || _ISOC99_SOURCE; or cc -std=c99
       log1pf(), log1pl(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE; or cc -std=c99

DESCRIPTION
       log1p(x) returns a value equivalent to

           log (1 + x)

       It is computed in a way that is accurate even if the value of x is near zero.

RETURN VALUE
       On success, these functions return the natural logarithm of (1 + x).

       If x is a NaN, a NaN is returned.

       If x is positive infinity, positive infinity is returned.

       If x is -1, a pole error occurs, and the functions return -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL, respectively.

       If  x  is  less  than  -1  (including  negative  infinity),  a domain error occurs, and a NaN (not a number) is
       returned.

ERRORS
       See math_error(7) for information on how to determine whether an error has occurred when  calling  these  func-
       tions.

       The following errors can occur:

       Domain error: x is less than -1
              An invalid floating-point exception (FE_INVALID) is raised.

       Pole error: x is -1
              A divide-by-zero floating-point exception (FE_DIVBYZERO) is raised.

       These functions do not set errno.

CONFORMING TO
       C99, POSIX.1-2001.

SEE ALSO
       exp(3), expm1(3), log(3)

COLOPHON
       This  page  is part of release 3.22 of the Linux man-pages project.  A description of the project, and informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



                                  2008-08-05                          LOG1P(3)