1EXP2(P)                    POSIX Programmer's Manual                   EXP2(P)
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NAME

6       exp2, exp2f, exp2l - exponential base 2 functions
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SYNOPSIS

9       #include <math.h>
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11       double exp2(double x);
12       float exp2f(float x);
13       long double exp2l(long double x);
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15

DESCRIPTION

17       These functions shall compute the base-2 exponential of x.
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19       An  application  wishing to check for error situations should set errno
20       to zero and  call  feclearexcept(FE_ALL_EXCEPT)  before  calling  these
21       functions.   On return, if errno is non-zero or fetestexcept(FE_INVALID
22       | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error  has
23       occurred.
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RETURN VALUE

26       Upon successful completion, these functions shall return 2**x.
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28       If  the  correct  value would cause overflow, a range error shall occur
29       and exp2(), exp2f(), and exp2l() shall return the value  of  the  macro
30       HUGE_VAL, HUGE_VALF, and HUGE_VALL, respectively.
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32       If the correct value would cause underflow, and is not representable, a
33       range error may occur, and    either 0.0 (if supported), or   an imple‐
34       mentation-defined value shall be returned.
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36       If x is NaN, a NaN shall be returned.
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38       If x is ±0, 1 shall be returned.
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40       If x is -Inf, +0 shall be returned.
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42       If x is +Inf, x shall be returned.
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44       If  the  correct  value  would cause underflow, and is representable, a
45       range error may occur and the correct value shall be returned.
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ERRORS

48       These functions shall fail if:
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50       Range Error
51              The result overflows.
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53       If the integer expression (math_errhandling & MATH_ERRNO) is  non-zero,
54       then  errno  shall  be  set  to  [ERANGE].  If  the  integer expression
55       (math_errhandling & MATH_ERREXCEPT)  is  non-zero,  then  the  overflow
56       floating-point exception shall be raised.
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59       These functions may fail if:
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61       Range Error
62              The result underflows.
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64       If  the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
65       then errno  shall  be  set  to  [ERANGE].  If  the  integer  expression
66       (math_errhandling  &  MATH_ERREXCEPT)  is  non-zero, then the underflow
67       floating-point exception shall be raised.
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69
70       The following sections are informative.
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EXAMPLES

73       None.
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APPLICATION USAGE

76       For IEEE Std 754-1985 double, 1024 <= x  implies  exp2(  x)  has  over‐
77       flowed. The value x < -1022 implies exp( x) has underflowed.
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79       On   error,   the   expressions  (math_errhandling  &  MATH_ERRNO)  and
80       (math_errhandling & MATH_ERREXCEPT) are independent of each other,  but
81       at least one of them must be non-zero.
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RATIONALE

84       None.
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FUTURE DIRECTIONS

87       None.
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SEE ALSO

90       exp()  ,  feclearexcept() , fetestexcept() , isnan() , log() , the Base
91       Definitions volume of IEEE Std 1003.1-2001, Section 4.18, Treatment  of
92       Error Conditions for Mathematical Functions, <math.h>
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95       Portions  of  this text are reprinted and reproduced in electronic form
96       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
97       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
98       Specifications Issue 6, Copyright (C) 2001-2003  by  the  Institute  of
99       Electrical  and  Electronics  Engineers, Inc and The Open Group. In the
100       event of any discrepancy between this version and the original IEEE and
101       The  Open Group Standard, the original IEEE and The Open Group Standard
102       is the referee document. The original Standard can be  obtained  online
103       at http://www.opengroup.org/unix/online.html .
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107IEEE/The Open Group                  2003                              EXP2(P)
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