номер точки (point number)
Пролог (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.
Имя (Name)
nextafter, nextafterf, nextafterl, nexttoward, nexttowardf,
nexttowardl — next representable floating-point number
Синопсис (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);
Описание (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.
Возвращаемое значение (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.
Ошибки (Error)
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.
Примеры (Examples)
None.
Использование в приложениях (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.
Обоснование (Rationale)
None.
Будущие направления (Future directions)
None.
Смотри также (See also)
feclearexcept(3p), fetestexcept(3p)
The Base Definitions volume of POSIX.1‐2017, Section 4.20,
Treatment of Error Conditions for Mathematical Functions,
math.h(0p), tgmath.h(0p)
