bionic (3) exp.3posix.gz

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

       exp, expf, expl — exponential function

SYNOPSIS

       #include <math.h>

       double exp(double x);
       float expf(float x);
       long double expl(long double x);

DESCRIPTION

       The  functionality  described  on  this  reference  page is aligned with the ISO C standard. Any conflict
       between the requirements described  here  and  the  ISO C  standard  is  unintentional.  This  volume  of
       POSIX.1‐2008 defers to the ISO C standard.

       These functions shall compute the base-e exponential of 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 exponential value of x.

       If  the correct value would cause overflow, a range error shall occur and exp(), expf(), and expl() shall
       return the value of the macro HUGE_VAL, HUGE_VALF, and HUGE_VALL, respectively.

       If the correct value would cause underflow, and is not representable, a range error may occur, and exp(),
       expf(),  and  expl()  shall  return  0.0, or (if the IEC 60559 Floating-Point option is not supported) an
       implementation-defined value no greater in magnitude than DBL_MIN, FLT_MIN, and LDBL_MIN, respectively.

       If x is NaN, a NaN shall be returned.

       If x is ±0, 1 shall be returned.

       If x is −Inf, +0 shall be returned.

       If x is +Inf, x shall be returned.

       If the correct value would cause underflow, and is representable, a range error may occur and the correct
       value shall be returned.

ERRORS

       These functions shall fail if:

       Range Error The result overflows.

                   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 overflow floating-point exception shall be raised.

       These functions may fail if:

       Range Error The result underflows.

                   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

   Computing the Density of the Standard Normal Distribution
       This  function  shows  an implementation for the density of the standard normal distribution using exp().
       This example uses the constant M_PI which is part of the XSI option.

           #include <math.h>

           double
           normal_density (double x)
           {
               return exp(−x*x/2) / sqrt (2*M_PI);
           }

APPLICATION USAGE

       Note that for IEEE Std 754‐1985 double, 709.8 < x implies exp(x)  has  overflowed.  The  value  x< −708.4
       implies exp(x) has underflowed.

       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(), isnan(), log()

       The Base Definitions volume of POSIX.1‐2008, Section 4.19, 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, 2013 Edition,
       Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open  Group  Base
       Specifications  Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc
       and The Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .

       Any  typographical  or formatting errors that appear in this page are most likely to have been introduced
       during  the  conversion  of  the  source  files  to  man  page  format.  To  report  such   errors,   see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .