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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():
       _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
           || _XOPEN_SOURCE >= 500
           || /* Since glibc 2.19: */ _DEFAULT_SOURCE
           || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
   log1pf(), log1pl():
       _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
           || /* Since glibc 2.19: */ _DEFAULT_SOURCE
           || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION

   These functions return a value equivalent to

       log (1 + x)

   The result 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 functions.

   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.

ATTRIBUTES

   For  an  explanation  of  the  terms  used   in   this   section,   see
   attributes(7).

   
   Interface                    Attribute      Value   
   
   log1p(), log1pf(), log1pl()  Thread safety  MT-Safe

CONFORMING TO

   C99, POSIX.1-2001, POSIX.1-2008.

SEE ALSO

   exp(3), expm1(3), log(3)

COLOPHON

   This  page  is  part of release 4.09 of the Linux man-pages project.  A
   description of the project, information about reporting bugs,  and  the
   latest     version     of     this    page,    can    be    found    at
   https://www.kernel.org/doc/man-pages/.

                              2016-03-15                          LOG1P(3)



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