This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

       The  relational  and  equality  operators  support  the  usual mathematical relationships between numeric
       values. For any ordered pair of numeric values, exactly one of  the  relationships  (less,  greater,  and
       equal)  is true. Relational operators may raise the invalid floating-point exception when argument values
       are NaNs. For a NaN and a numeric value, or for two NaNs, just the unordered relationship is  true.  This
       macro  is a quiet (non-floating-point exception raising) version of a relational operator. It facilitates
       writing efficient code that accounts for NaNs without suffering the invalid floating-point exception.  In
       the  SYNOPSIS  section, real-floating indicates that the argument shall be an expression of real-floating
       type.

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group  Base
       Specifications  Issue  7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  In the event of any discrepancy between this version and the original
       IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee  document.
       The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

       Any  typographical  or formatting errors that appear in this page are most likely to have been introduced
       during  the  conversion  of  the  source  files  to  man  page  format.  To  report  such   errors,   see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2017                                   ISLESSEQUAL(3POSIX)

       The  functionality  described  on  this  reference  page is aligned with the ISO C standard. Any conflict
       between the requirements described  here  and  the  ISO C  standard  is  unintentional.  This  volume  of
       POSIX.1‐2017 defers to the ISO C standard.

       The  islessequal()  macro  shall determine whether its first argument is less than or equal to its second
       argument. The value of islessequal(x, y) shall  be  equal  to  (x) <= (y);  however,  unlike  (x) <= (y),
       islessequal(x, y) shall not raise the invalid floating-point exception when x and y are unordered.

       No errors are defined.

       Thefollowingsectionsareinformative.

       None.

       None.

       islessequal — test if x is less than or equal to y

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult the corresponding Linux manual page for details of Linux behavior), or the  interface
       may not be implemented on Linux.

       None.

       Upon successful completion, the islessequal() macro shall return the value of (x) <= (y).

       If x or y is NaN, 0 shall be returned.

isgreater(), isgreaterequal(), isless(), islessgreater(), isunordered()

       The Base Definitions volume of POSIX.1‐2017, <math.h>

       #include <math.h>

       int islessequal(real-floating x, real-floating y);