# exp

## 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.1‐2017 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



           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.
    


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