вычислить экспоненту с помощью FLT_RADIX (compute exponent using FLT_RADIX)
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)
scalbln, scalblnf, scalblnl, scalbn, scalbnf, scalbnl — compute
exponent using FLT_RADIX
Синопсис (Synopsis)
#include <math.h>
double scalbln(double x, long n);
float scalblnf(float x, long n);
long double scalblnl(long double x, long n);
double scalbn(double x, int n);
float scalbnf(float x, int n);
long double scalbnl(long double x, int n);
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.
These functions shall compute x * FLT_RADIXn efficiently, not
normally by computing FLT_RADIXn explicitly.
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
x * FLT_RADIXn.
If the result would cause overflow, a range error shall occur and
these functions shall return ±HUGE_VAL, ±HUGE_VALF, and
±HUGE_VALL (according to the sign of x) as appropriate for the
return type of the function.
If the correct value would cause underflow, and is not
representable, a range error may occur, and scalbln(),
scalblnf(), scalblnl(), scalbn(), scalbnf(), and scalbnl() shall
return 0.0, or (if IEC 60559 Floating-Point is not supported) an
implementation-defined value no greater in magnitude than
DBL_MIN, FLT_MIN, LDBL_MIN, DBL_MIN, FLT_MIN, and LDBL_MIN,
respectively.
If x is NaN, a NaN shall be returned.
If x is ±0 or ±Inf, x shall be returned.
If n is 0, x shall be returned.
If the correct value would cause underflow, and is representable,
a range error may occur and the correct value shall be returned.
Ошибки (Error)
These functions shall fail if:
Range Error The result 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.
These functions may fail if:
Range Error The result 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.
Обоснование (Rationale)
These functions are named so as to avoid conflicting with the
historical definition of the scalb() function from the Single
UNIX Specification. The difference is that the scalb() function
has a second argument of double instead of int. The scalb()
function is not part of the ISO C standard. The three functions
whose second type is long are provided because the factor
required to scale from the smallest positive floating-point value
to the largest finite one, on many implementations, is too large
to represent in the minimum-width int format.
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)
