NAME

       exp2, exp2f, exp2l - exponential base 2 functions

SYNOPSIS

       #include <math.h>

       double exp2(double x);
       float exp2f(float x);
       long double exp2l(long double x);

DESCRIPTION

       These functions shall compute the base-2 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 2**x.

       If the correct value would cause overflow, a range error shall occur and exp2(),  exp2f(),
       and  exp2l()  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     either  0.0  (if supported), or   an implementation-defined value shall be
       returned.

       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

       None.

APPLICATION USAGE

       For  IEEE Std 754-1985  double,  1024  <=  x  implies exp2( x) has overflowed. The value x
       < -1022 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

       exp()  ,  feclearexcept() , fetestexcept() , isnan() , 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 .