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

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

SYNOPSIS
       #include 

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

       Link with -lm.

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

       log1p():
           BSDSOURCE || SVIDSOURCE || XOPENSOURCE >= 500 ||
           XOPENSOURCE && XOPENSOURCEEXTENDED || ISOC99SOURCE ||
           POSIXCSOURCE >= 200112L;
           or cc -std=c99
       log1pf(), log1pl():
           BSDSOURCE || SVIDSOURCE || XOPENSOURCE >= 600 ||
           ISOC99SOURCE || POSIXCSOURCE >= 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 -HUGEVAL,
       -HUGEVALF, or -HUGEVALL, respectively.

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

ERRORS
       See  matherror(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 (FEINVALID) is raised.

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

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)