1EXP(3P) POSIX Programmer's Manual EXP(3P)
2
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
13 exp, expf, expl — exponential function
14
16 #include <math.h>
17 double exp(double x);
19 float expf(float x);
20 long double expl(long double x);
21
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.
27 These functions shall compute the base-e exponential of x.
29 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.
35
37 Upon successful completion, these functions shall return the exponen‐
38 tial value of x.
39 If the correct value would cause overflow, a range error shall occur
41 and exp(), expf(), and expl() shall return the value of the macro
42 HUGE_VAL, HUGE_VALF, and HUGE_VALL, respectively.
43 If the correct value would cause underflow, and is not representable, a
45 range error may occur, and exp(), expf(), and expl() shall return 0.0,
46 or (if the IEC 60559 Floating-Point option is not supported) an imple‐
47 mentation-defined value no greater in magnitude than DBL_MIN, FLT_MIN,
48 and LDBL_MIN, respectively.
49 If x is NaN, a NaN shall be returned.
51 If x is ±0, 1 shall be returned.
53 If x is −Inf, +0 shall be returned.
55 If x is +Inf, x shall be returned.
57 If the correct value would cause underflow, and is representable, a
59 range error may occur and the correct value shall be returned.
60
62 These functions shall fail if:
63 Range Error The result overflows.
65 If the integer expression (math_errhandling & MATH_ERRNO)
67 is non-zero, then errno shall be set to [ERANGE]. If the
68 integer expression (math_errhandling & MATH_ERREXCEPT) is
69 non-zero, then the overflow floating-point exception shall
70 be raised.
71 These functions may fail if:
73 Range Error The result underflows.
75 If the integer expression (math_errhandling & MATH_ERRNO)
77 is non-zero, then errno shall be set to [ERANGE]. If the
78 integer expression (math_errhandling & MATH_ERREXCEPT) is
79 non-zero, then the underflow floating-point exception shall
80 be raised.
81 The following sections are informative.
83
85 Computing the Density of the Standard Normal Distribution
86 This function shows an implementation for the density of the standard
87 normal distribution using exp(). This example uses the constant M_PI
88 which is part of the XSI option.
89 #include <math.h>
91 double
93 normal_density (double x)
94 {
95 return exp(−x*x/2) / sqrt (2*M_PI);
96 }
97
99 Note that for IEEE Std 754‐1985 double, 709.8 < x implies exp(x) has
100 overflowed. The value x< −708.4 implies exp(x) has underflowed.
101 On error, the expressions (math_errhandling & MATH_ERRNO) and
103 (math_errhandling & MATH_ERREXCEPT) are independent of each other, but
104 at least one of them must be non-zero.
105
107 None.
108
110 None.
111
113 feclearexcept(), fetestexcept(), isnan(), log()
114 The Base Definitions volume of POSIX.1‐2008, Section 4.19, Treatment of
116 Error Conditions for Mathematical Functions, <math.h>
117
119 Portions of this text are reprinted and reproduced in electronic form
120 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
121 -- Portable Operating System Interface (POSIX), The Open Group Base
122 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
123 cal and Electronics Engineers, Inc and The Open Group. (This is
124 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
125 event of any discrepancy between this version and the original IEEE and
126 The Open Group Standard, the original IEEE and The Open Group Standard
127 is the referee document. The original Standard can be obtained online
128 at http://www.unix.org/online.html .
129 Any typographical or formatting errors that appear in this page are
131 most likely to have been introduced during the conversion of the source
132 files to man page format. To report such errors, see https://www.ker‐
133 nel.org/doc/man-pages/reporting_bugs.html .
134IEEE/The Open Group 2013 EXP(3P)