expm1l(3)

1EXPM1(3)                   Linux Programmer's Manual                  EXPM1(3)
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NAME

6       expm1, expm1f, expm1l - exponential minus 1
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SYNOPSIS

9       #include <math.h>
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11       double expm1(double x);
12       float expm1f(float x);
13       long double expm1l(long double x);
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15       Link with -lm.
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17   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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19       expm1():
20           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
21               || _XOPEN_SOURCE >= 500
22               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
23               || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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25       expm1f(), expm1l():
26           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
27               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
28               || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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DESCRIPTION

31       These functions return a value equivalent to
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33           exp(x) - 1
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35       The result is computed in a way that is accurate even if the value of x
36       is near zero—a case where exp(x) - 1 would be inaccurate  due  to  sub‐
37       traction of two numbers that are nearly equal.
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RETURN VALUE

40       On success, these functions return exp(x) - 1.
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42       If x is a NaN, a NaN is returned.
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44       If x is +0 (-0), +0 (-0) is returned.
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46       If x is positive infinity, positive infinity is returned.
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48       If x is negative infinity, -1 is returned.
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50       If the result overflows, a range error occurs, and the functions return
51       -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL, respectively.
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ERRORS

54       See math_error(7) for information on how to determine whether an  error
55       has occurred when calling these functions.
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57       The following errors can occur:
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59       Range error, overflow
60              errno  is  set  to ERANGE (but see BUGS).  An overflow floating-
61              point exception (FE_OVERFLOW) is raised.
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ATTRIBUTES

64       For an  explanation  of  the  terms  used  in  this  section,  see  at‐
65       tributes(7).
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67       ┌────────────────────────────────────────────┬───────────────┬─────────┐
68       │Interface                                   │ Attribute     │ Value   │
69       ├────────────────────────────────────────────┼───────────────┼─────────┤
70       │expm1(), expm1f(), expm1l()                 │ Thread safety │ MT-Safe │
71       └────────────────────────────────────────────┴───────────────┴─────────┘
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CONFORMING TO

74       C99, POSIX.1-2001, POSIX.1-2008.
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BUGS

77       Before glibc 2.17, on certain architectures (e.g., x86, but not x86_64)
78       expm1() raised a bogus  underflow  floating-point  exception  for  some
79       large negative x values (where the function result approaches -1).
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81       Before approximately glibc version 2.11, expm1() raised a bogus invalid
82       floating-point exception in addition to the  expected  overflow  excep‐
83       tion,  and  returned a NaN instead of positive infinity, for some large
84       positive x values.
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86       Before version 2.11, the glibc implementation  did  not  set  errno  to
87       ERANGE when a range error occurred.
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COLOPHON

93       This  page  is  part of release 5.13 of the Linux man-pages project.  A
94       description of the project, information about reporting bugs,  and  the
95       latest     version     of     this    page,    can    be    found    at
96       https://www.kernel.org/doc/man-pages/.
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100                                  2021-03-22                          EXPM1(3)