NEXTAFTER(3P)                                       POSIX Programmer's Manual                                      NEXTAFTER(3P)



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult 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  nextafter(), nextafterf(), and nextafterl() functions shall compute the next representable floating-point value fol-
       lowing 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() func-
       tions, 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 either the cor-
       rect 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  inte-
       ger  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  inte-
       ger  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.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       feclearexcept(),  fetestexcept(),  the  Base Definitions volume of IEEE Std 1003.1-2001, Section 4.18, Treatment of Error
       Conditions for Mathematical Functions, <math.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003  Edition,  Standard  for
       Information  Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copy-
       right (C) 2001-2003 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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                 NEXTAFTER(3P)