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.1‐2008 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.1‐2008, Section 4.19, 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,  2013  Edition,  Standard  for Information Technology -- Portable Operating System
       Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013  by  the
       Institute  of  Electrical  and  Electronics  Engineers,  Inc and The Open Group.  (This is
       POSIX.1-2008 with the  2013  Technical  Corrigendum  1  applied.)  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.unix.org/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 .