PROLOG

       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.

NAME

       nextafter,   nextafterf,   nextafterl,   nexttoward,   nexttowardf,   nexttowardl  —  next
       representable floating-point number

SYNOPSIS

       #include <math.h>

       double nextafter(double x, double y);
       float nextafterf(float x, float y);
       long double nextafterl(long double x, long double y);
       double nexttoward(double x, long double y);
       float nexttowardf(float x, long double y);
       long double nexttowardl(long double x, long double y);

DESCRIPTION

       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  nextafter(),  nextafterf(),  and  nextafterl()  functions  shall  compute  the   next
       representable  floating-point value following x in the direction of y.  Thus, if y is less
       than x, nextafter() shall return the largest representable floating-point number less than
       x.   The  nextafter(), nextafterf(), and nextafterl() functions shall return y if x equals
       y.

       The nexttoward(), nexttowardf(), and nexttowardl() functions shall be  equivalent  to  the
       corresponding nextafter() functions, except that the second parameter shall have type long
       double and the functions shall return y converted to the type of the function if x  equals
       y.

       An  application  wishing  to  check for error situations should set errno to zero and call
       feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if errno  is  non-
       zero  or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero,
       an error has occurred.

RETURN VALUE

       Upon successful completion, these functions shall return the next representable  floating-
       point value following x in the direction of y.

       If x==y, y (of the type x) shall be returned.

       If  x  is  finite and the correct function value would overflow, a range error shall occur
       and ±HUGE_VAL, ±HUGE_VALF, and ±HUGE_VALL (with the same sign as x) shall be  returned  as
       appropriate for the return type of the function.

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

       If  x!=y  and  the correct function value is subnormal, zero, or underflows, a range error
       shall occur, and
       the correct function value (if representable) or
       0.0 shall be returned.

ERRORS

       These functions shall fail if:

       Range Error The correct value overflows.

                   If the integer expression (math_errhandling & MATH_ERRNO)  is  non-zero,  then
                   errno shall be set to [ERANGE].  If the integer expression (math_errhandling &
                   MATH_ERREXCEPT) is non-zero, then the overflow floating-point exception  shall
                   be raised.

       Range Error The correct value is subnormal or underflows.

                   If  the  integer  expression (math_errhandling & MATH_ERRNO) is non-zero, then
                   errno shall be set to [ERANGE].  If the integer expression (math_errhandling &
                   MATH_ERREXCEPT) is non-zero, then the underflow floating-point exception shall
                   be raised.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       On  error,  the  expressions  (math_errhandling  &  MATH_ERRNO)  and  (math_errhandling  &
       MATH_ERREXCEPT) are independent of each other, but at least one of them must be non-zero.

       When  <tgmath.h>  is  included,  note  that  the return type of nextafter() depends on the
       generic typing deduced from both arguments, while the return type of nexttoward()  depends
       only on the generic typing of the first argument.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       feclearexcept(), fetestexcept()

       The  Base  Definitions volume of POSIX.1‐2017, Section 4.20, Treatment of Error Conditions
       for Mathematical Functions, <math.h>, <tgmath.h>

COPYRIGHT

       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 .