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LOG1P(3P)                  POSIX Programmer's Manual                 LOG1P(3P)

PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the  corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.
NAME
       log1p, log1pf, log1pl - compute a natural logarithm
SYNOPSIS
       #include <math.h>
       double log1p(double x);
       float log1pf(float x);
       long double log1pl(long double x);

DESCRIPTION
       These functions shall compute log_e(1.0 + x).
       An application wishing to check for error situations should  set  errno
       to  zero  and  call  feclearexcept(FE_ALL_EXCEPT)  before calling these
       functions.  On return, if errno is non-zero or  fetestexcept(FE_INVALID
       |  FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has
       occurred.
RETURN VALUE
       Upon successful completion, these functions shall  return  the  natural
       logarithm of 1.0 + x.
       If  x  is  -1,  a  pole  error  shall  occur and log1p(), log1pf(), and
       log1pl() shall return -HUGE_VAL, -HUGE_VALF,  and  -HUGE_VALL,  respec-
       tively.
       For  finite  values  of  x  that are less than -1,  or if x is -Inf,  a
       domain error shall occur, and  either  a  NaN  (if  supported),  or  an
       implementation-defined value shall be returned.
       If x is NaN, a NaN shall be returned.
       If x is +-0, or +Inf, x shall be returned.
       If x is subnormal, a range error may occur and x should be returned.
ERRORS
       These functions shall fail if:
       Domain Error
              The finite value of x is less than -1,  or x is -Inf.
       If  the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
       then  errno  shall  be  set  to  [EDOM].  If  the  integer   expression
       (math_errhandling  &  MATH_ERREXCEPT)  is  non-zero,  then  the invalid
       floating-point exception shall be raised.
       Pole Error
              The value of x is -1.
       If the integer expression (math_errhandling & MATH_ERRNO) is  non-zero,
       then  errno  shall  be  set  to  [ERANGE].  If  the  integer expression
       (math_errhandling & MATH_ERREXCEPT) is non-zero,  then  the  divide-by-
       zero floating-point exception shall be raised.

       These functions may fail if:
       Range Error
              The value of x is subnormal.
       If  the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
       then errno  shall  be  set  to  [ERANGE].  If  the  integer  expression
       (math_errhandling  &  MATH_ERREXCEPT)  is  non-zero, then the underflow
       floating-point exception shall be raised.

       The following sections are informative.
EXAMPLES
       None.
APPLICATION USAGE
       On  error,  the  expressions  (math_errhandling   &   MATH_ERRNO)   and
       (math_errhandling  & MATH_ERREXCEPT) are independent of each other, but
       at least one of them must be non-zero.
RATIONALE
       None.
FUTURE DIRECTIONS
       None.
SEE ALSO
       feclearexcept(), fetestexcept(), log(), the Base Definitions volume  of
       IEEE Std 1003.1-2001,  Section  4.18, Treatment of Error Conditions for
       Mathematical Functions, <math.h>
COPYRIGHT
       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
       Specifications  Issue  6,  Copyright  (C) 2001-2003 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open  Group.  In  the
       event of any discrepancy between this version and the original IEEE and
       The Open Group Standard, the original IEEE and The Open Group  Standard
       is  the  referee document. The original Standard can be obtained online
       at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group                  2003                            LOG1P(3P)