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EXPM1(3) Linux Programmer's Manual 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 functions
    return -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL,
    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:



  

  
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).



  

    Interface
    Attribute
    Value
  

  

    expm1 (), expm1f (), expm1l ()
    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 function 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/.







  

    2020-06-09