expm1f(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(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 ||
20       _ISOC99_SOURCE; or cc -std=c99
21       expm1f(), expm1l(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600
22       || _ISOC99_SOURCE; or cc -std=c99
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DESCRIPTION

25       expm1(x) returns a value equivalent to
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27           exp(x) - 1
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29       It is computed in a way that is accurate even if the value of x is near
30       zero—a case where exp(x) - 1 would be inaccurate due to subtraction  of
31       two numbers that are nearly equal.
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RETURN VALUE

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

48       See math_error(7) for information on how to determine whether an  error
49       has occurred when calling these functions.
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51       The following errors can occur:
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53       Range error, overflow
54              An overflow floating-point exception (FE_OVERFLOW) is raised.
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56       These functions do not set errno.
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CONFORMING TO

59       C99, POSIX.1-2001.
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BUGS

62       For  some large negative x values (where the function result approaches
63       -1), expm1() raises a bogus underflow floating-point exception.
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65       For some large positive x values, expm1() raises a bogus invalid float‐
66       ing-point exception in addition to the expected overflow exception, and
67       returns a NaN instead of positive infinity.
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COLOPHON

73       This page is part of release 3.25 of the Linux  man-pages  project.   A
74       description  of  the project, and information about reporting bugs, can
75       be found at http://www.kernel.org/doc/man-pages/.
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79                                  2008-08-05                          EXPM1(3)