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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 ||
           _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED || _ISOC99_SOURCE ||
           _POSIX_C_SOURCE >= 200112L;
           or cc -std=c99
       log1pf(), log1pl():
           _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 ||
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
           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 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.
CONFORMING TO
       C99, POSIX.1-2001.
SEE ALSO
       exp(3), expm1(3), log(3)
COLOPHON
       This  page  is  part of release 3.53 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

                                  2010-09-20                          LOG1P(3)