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

       The integral value returned by these functions might not be expressible as an intmax_t.  The return value
       should be tested before assigning it to an integer type to avoid the  undefined  results  of  an  integer
       overflow.

       These  functions  may  raise the inexact floating-point exception if the result differs in value from the
       argument.

       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                                         FLOOR(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.

       These functions shall compute the largest integral value not greater than x.

       No errors are defined.

       Thefollowingsectionsareinformative.

       None.

       None.

       floor, floorf, floorl — floor function

       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.

       The result shall have the same sign as x.

       Upon  successful  completion, these functions shall return the largest integral value not greater than x,
       expressed as a double, float, or longdouble, as appropriate for the return type of the function.

       If x is NaN, a NaN shall be returned.

       If x is ±0 or ±Inf, x shall be returned.

ceil(), feclearexcept(), fetestexcept(), isnan()

       Section4.20, TreatmentofErrorConditionsforMathematicalFunctions, <math.h>

       #include <math.h>

       double floor(double x);
       float floorf(float x);
       long double floorl(long double x);