1EXP(3P)                    POSIX Programmer's Manual                   EXP(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.
10

NAME

12       exp, expf, expl — exponential function
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SYNOPSIS

15       #include <math.h>
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17       double exp(double x);
18       float expf(float x);
19       long double expl(long double x);
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DESCRIPTION

22       The functionality described on this reference page is aligned with  the
23       ISO C  standard.  Any  conflict between the requirements described here
24       and the ISO C standard is unintentional. This  volume  of  POSIX.1‐2017
25       defers to the ISO C standard.
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27       These functions shall compute the base-e exponential of x.
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29       An  application  wishing to check for error situations should set errno
30       to zero and  call  feclearexcept(FE_ALL_EXCEPT)  before  calling  these
31       functions. On return, if errno is non-zero or fetestexcept(FE_INVALID |
32       FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero,  an  error  has
33       occurred.
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RETURN VALUE

36       Upon  successful  completion, these functions shall return the exponen‐
37       tial value of x.
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39       If the correct value would cause overflow, a range  error  shall  occur
40       and  exp(),  expf(),  and  expl()  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 exp(), expf(), and expl() shall return 0.0,
45       or (if the IEC 60559 Floating-Point option is not supported) an  imple‐
46       mentation-defined  value no greater in magnitude than DBL_MIN, FLT_MIN,
47       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   Computing the Density of the Standard Normal Distribution
85       This  function  shows an implementation for the density of the standard
86       normal distribution using exp().  This example uses the  constant  M_PI
87       which is part of the XSI option.
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89
90           #include <math.h>
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92           double
93           normal_density (double x)
94           {
95               return exp(-x*x/2) / sqrt (2*M_PI);
96           }
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APPLICATION USAGE

99       On   error,   the   expressions  (math_errhandling  &  MATH_ERRNO)  and
100       (math_errhandling & MATH_ERREXCEPT) are independent of each other,  but
101       at least one of them must be non-zero.
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RATIONALE

104       None.
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FUTURE DIRECTIONS

107       None.
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SEE ALSO

110       feclearexcept(), fetestexcept(), isnan(), log()
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112       The Base Definitions volume of POSIX.1‐2017, Section 4.20, Treatment of
113       Error Conditions for Mathematical Functions, <math.h>
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116       Portions of this text are reprinted and reproduced in  electronic  form
117       from  IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
118       table Operating System Interface (POSIX), The Open Group Base  Specifi‐
119       cations  Issue  7, 2018 Edition, Copyright (C) 2018 by the Institute of
120       Electrical and Electronics Engineers, Inc and The Open Group.   In  the
121       event of any discrepancy between this version and the original IEEE and
122       The Open Group Standard, the original IEEE and The Open Group  Standard
123       is  the  referee document. The original Standard can be obtained online
124       at http://www.opengroup.org/unix/online.html .
125
126       Any typographical or formatting errors that appear  in  this  page  are
127       most likely to have been introduced during the conversion of the source
128       files to man page format. To report such errors,  see  https://www.ker‐
129       nel.org/doc/man-pages/reporting_bugs.html .
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133IEEE/The Open Group                  2017                              EXP(3P)
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