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():
           _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
              errno  is set to EDOM (but see BUGS).  An invalid floating-point
              exception (FE_INVALID) is raised.

       Pole error: x is -1
              errno is set to ERANGE (but see BUGS).  A divide-by-zero  float-
              ing-point exception (FE_DIVBYZERO) is raised.

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

       allbox; lbw27 lb lb  l  l  l.   Interface Attribute Value  T{  log1p(),
       log1pf(), log1pl() T}   Thread safety  MT-Safe

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

BUGS
       Before version 2.22, the glibc implementation did not set errno to EDOM
       when a domain error occurred.

       Before version 2.22, the glibc implementation  did  not  set  errno  to
       ERANGE when a range error occurred.

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

COLOPHON
       This  page  is  part of release 4.16 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/.



                                  2017-09-15                          LOG1P(3)