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EXP2(3P)                   POSIX Programmer's Manual                  EXP2(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
       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 implemen-
       tation-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 over-
       flowed. 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  Defi-
       nitions  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                             EXP2(3P)