IEEE Std 1003.1-2008, 2016 Edition

Copyright © 2001-2016 The IEEE and The Open Group

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

#include <math.h>

double nextafter(doublex, doubley);

float nextafterf(floatx, floaty);

long double nextafterl(long doublex, long doubley);

double nexttoward(doublex, long doubley);

float nexttowardf(floatx, long doubley);

long double nexttowardl(long doublex, long doubley);

^{[CX]}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(), andnextafterl() functions shall compute the next representable floating-point value followingxin the direction ofy. Thus, ifyis less thanx,nextafter() shall return the largest representable floating-point number less thanx. Thenextafter(),nextafterf(), andnextafterl() functions shall returnyifxequalsy.The

nexttoward(),nexttowardf(), andnexttowardl() functions shall be equivalent to the correspondingnextafter() functions, except that the second parameter shall have typelong doubleand the functions shall returnyconverted to the type of the function ifxequalsy.An application wishing to check for error situations should set

errnoto zero and callfeclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, iferrnois non-zero orfetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.

Upon successful completion, these functions shall return the next representable floating-point value following

xin the direction ofy.If

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

xis 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 asx) shall be returned as appropriate for the return type of the function.

^{[MX]}Ifxoryis NaN, a NaN shall be returned.

^{[MX]}Ifx!=yand the correct function value is subnormal, zero, or underflows, a range error shall occur, and

^{[MXX]}the correct function value (if representable) or

^{[MX]}0.0 shall be returned.

These functions shall fail if:

- Range Error
- The correct value overflows.
If the integer expression (

math_errhandling& MATH_ERRNO) is non-zero, thenerrnoshall 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
^{[MX]}The correct value is subnormal or underflows.If the integer expression (

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

None.

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 ofnextafter() depends on the generic typing deduced from both arguments, while the return type ofnexttoward() depends only on the generic typing of the first argument.

None.

None.

XBD

Treatment of Error Conditions for Mathematical Functions,<math.h>,<tgmath.h>

First released in Issue 4, Version 2.

Moved from X/OPEN UNIX extension to BASE.

The

nextafter() function is no longer marked as an extension.The

nextafterf(),nextafterl(),nexttoward(),nexttowardf(), andnexttowardl() functions are added for alignment with the ISO/IEC 9899:1999 standard.The DESCRIPTION, RETURN VALUE, ERRORS, and APPLICATION USAGE sections are revised to align with the ISO/IEC 9899:1999 standard.

IEC 60559:1989 standard floating-point extensions over the ISO/IEC 9899:1999 standard are marked.

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0407 [68] and XSH/TC1-2008/0408 [357] are applied.

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