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EXP(3P)                    POSIX Programmer's Manual                   EXP(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
       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 exponen-
       tial 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  imple-
       mentation-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 Electri-
       cal  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.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                              EXP(3P)