1EXP2(3P)                   POSIX Programmer's Manual                  EXP2(3P)
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PROLOG

6       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
7       implementation of this interface may differ (consult the  corresponding
8       Linux  manual page for details of Linux behavior), or the interface may
9       not be implemented on Linux.
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11

NAME

13       exp2, exp2f, exp2l — exponential base 2 functions
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SYNOPSIS

16       #include <math.h>
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18       double exp2(double x);
19       float exp2f(float x);
20       long double exp2l(long double x);
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DESCRIPTION

23       The functionality described on this reference page is aligned with  the
24       ISO C  standard.  Any  conflict between the requirements described here
25       and the ISO C standard is unintentional. This  volume  of  POSIX.1‐2008
26       defers to the ISO C standard.
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28       These functions shall compute the base-2 exponential of x.
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30       An  application  wishing to check for error situations should set errno
31       to zero and  call  feclearexcept(FE_ALL_EXCEPT)  before  calling  these
32       functions. On return, if errno is non-zero or fetestexcept(FE_INVALID |
33       FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero,  an  error  has
34       occurred.
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RETURN VALUE

37       Upon successful completion, these functions shall return 2x.
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39       If  the  correct  value would cause overflow, a range error shall occur
40       and exp2(), exp2f(), and exp2l() shall return the value  of  the  macro
41       HUGE_VAL, HUGE_VALF, and HUGE_VALL, respectively.
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43       If the correct value would cause underflow, and is not representable, a
44       range error may occur, and exp2(), exp2f(), and  exp2l()  shall  return
45       0.0,  or  (if  the IEC 60559 Floating-Point option is not supported) an
46       implementation-defined value no  greater  in  magnitude  than  DBL_MIN,
47       FLT_MIN, and LDBL_MIN, respectively.
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49       If x is NaN, a NaN shall be returned.
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51       If x is ±0, 1 shall be returned.
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53       If x is −Inf, +0 shall be returned.
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55       If x is +Inf, x shall be returned.
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57       If  the  correct  value  would cause underflow, and is representable, a
58       range error may occur and the correct value shall be returned.
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ERRORS

61       These functions shall fail if:
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63       Range Error The result overflows.
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65                   If the integer expression (math_errhandling  &  MATH_ERRNO)
66                   is  non-zero,  then errno shall be set to [ERANGE].  If the
67                   integer expression (math_errhandling &  MATH_ERREXCEPT)  is
68                   non-zero,  then the overflow floating-point exception shall
69                   be raised.
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71       These functions may fail if:
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73       Range Error The result underflows.
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75                   If the integer expression (math_errhandling  &  MATH_ERRNO)
76                   is  non-zero,  then errno shall be set to [ERANGE].  If the
77                   integer expression (math_errhandling &  MATH_ERREXCEPT)  is
78                   non-zero, then the underflow floating-point exception shall
79                   be raised.
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81       The following sections are informative.
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EXAMPLES

84       None.
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APPLICATION USAGE

87       For IEEE Std 754‐1985 double, 1024 <= x implies exp2(x) has overflowed.
88       The value x< −1022 implies exp(x) has underflowed.
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90       On   error,   the   expressions  (math_errhandling  &  MATH_ERRNO)  and
91       (math_errhandling & MATH_ERREXCEPT) are independent of each other,  but
92       at least one of them must be non-zero.
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RATIONALE

95       None.
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FUTURE DIRECTIONS

98       None.
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SEE ALSO

101       exp(), feclearexcept(), fetestexcept(), isnan(), log()
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103       The Base Definitions volume of POSIX.1‐2008, Section 4.19, Treatment of
104       Error Conditions for Mathematical Functions, <math.h>
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107       Portions of this text are reprinted and reproduced in  electronic  form
108       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
109       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
110       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
111       cal and Electronics Engineers,  Inc  and  The  Open  Group.   (This  is
112       POSIX.1-2008  with  the  2013  Technical Corrigendum 1 applied.) In the
113       event of any discrepancy between this version and the original IEEE and
114       The  Open Group Standard, the original IEEE and The Open Group Standard
115       is the referee document. The original Standard can be  obtained  online
116       at http://www.unix.org/online.html .
117
118       Any  typographical  or  formatting  errors that appear in this page are
119       most likely to have been introduced during the conversion of the source
120       files  to  man page format. To report such errors, see https://www.ker‐
121       nel.org/doc/man-pages/reporting_bugs.html .
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125IEEE/The Open Group                  2013                             EXP2(3P)
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