EXPM1(3)                  (2020-06-09)                   EXPM1(3)

     NAME
          expm1, expm1f, expm1l - exponential minus 1

     SYNOPSIS
          #include <math.h>

          double expm1(double x);
          float expm1f(float x);
          long double expm1l(long double x);

          Link with -lm.

     Feature Test Macro Requirements for glibc (see
     feature_test_macros(7)):

          expm1():
              _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
                  || _XOPEN_SOURCE >= 500
                  || /* Since glibc 2.19: */ _DEFAULT_SOURCE
                  || /* Glibc versions <= 2.19: */ _BSD_SOURCE ||
              _SVID_SOURCE
          expm1f(), expm1l():
              _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
                  || /* Since glibc 2.19: */ _DEFAULT_SOURCE
                  || /* Glibc versions <= 2.19: */ _BSD_SOURCE ||
              _SVID_SOURCE

     DESCRIPTION
          These functions return a value equivalent to

              exp(x) - 1

          The result is computed in a way that is accurate even if the
          value  of  x  is  near zero-a case where exp(x) - 1 would be
          inaccurate due to subtraction of two numbers that are nearly
          equal.

     RETURN VALUE
          On success, these functions return exp(x) - 1.

          If x is a NaN, a NaN is returned.

          If x is +0 (-0), +0 (-0) is returned.

          If x is positive infinity, positive infinity is returned.

          If x is negative infinity, -1 is returned.

          If the result overflows, a range error occurs, and the func-
          tions   return   -HUGE_VAL,   -HUGE_VALF,   or   -HUGE_VALL,

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     EXPM1(3)                  (2020-06-09)                   EXPM1(3)

          respectively.

     ERRORS
          See  math_error(7)  for  information  on  how  to  determine
          whether an error has occurred when calling these functions.

          The following errors can occur:

          Range error, overflow
               errno is set to ERANGE (but  see  BUGS).   An  overflow
               floating-point exception (FE_OVERFLOW) is raised.

     ATTRIBUTES
          For an explanation of the terms used in  this  section,  see
          attributes(7).     allbox;    lbw27    lb    lb   l   l   l.
          Interface Attribute Value  T{  expm1(),  expm1f(),  expm1l()
          T}   Thread safety  MT-Safe

     CONFORMING TO
          C99, POSIX.1-2001, POSIX.1-2008.

     BUGS
          Before glibc 2.17, on certain architectures (e.g., x86,  but
          not  x86_64) expm1() raised a bogus underflow floating-point
          exception for some large negative x values (where the  func-
          tion result approaches -1),

          Before approximately glibc version 2.11,  expm1()  raised  a
          bogus  invalid  floating-point  exception in addition to the
          expected overflow exception, and returned a NaN  instead  of
          positive infinity.  for some large positive x values,

          Before version 2.11, the glibc implementation  did  not  set
          errno to ERANGE when a range error occurred.

     SEE ALSO
          exp(3), log(3), log1p(3)

     COLOPHON
          This page is part of release 5.10  of  the  Linux  man-pages
          project.   A  description  of the project, information about
          reporting bugs, and the latest version of this page, can  be
          found at https://www.kernel.org/doc/man-pages/.

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