scalbn(), scalbnf(), scalbnl()

Load the exponent of a radix-independent floating point number

Synopsis:

#include <math.h>

double scalbn ( double x,
                int n );

float scalbnf ( float x,
                int n );

long double scalbnl ( long double x,
                      int n );

Arguments:

x: The floating point number that you want to multiply by the exponent.
n: The exponent to apply to the radix of the machine's floating-point arithmetic.

Library:

libm

Use the -l m option to qcc to link against this library.

Description:

The scalbn(), scalbnf(), and scalbnl() functions compute x × rⁿ, where r is the radix of the machine's floating-point arithmetic. The difference between the scalbn* and scalbln* functions is the type of the second argument.

To check for error situations, use feclearexcept() and fetestexcept(). For example:

Call feclearexcept(FE_ALL_EXCEPT) before calling scalbn(), scalbnf(), or scalbnl().
On return, if fetestexcept(FE_ALL_EXCEPT) is nonzero, then an error has occurred.

Returns:

x × rⁿ

If:	These functions return:	Errors:
`x` is NaN	NaN	—
`x` is ±0.0 or ±Inf	`x`	—
`n` is 0	`x`	—
The correct value would cause underflow	The correct value, after rounding	FE_UNDERFLOW
The correct value would cause overflow	Inf	FE_OVERFLOW

These functions raise FE_INEXACT if the FPU reports that the result can't be exactly represented as a floating-point number.

Examples:

#include <stdio.h>
#include <inttypes.h>
#include <math.h>
#include <fenv.h>
#include <stdlib.h>

int main( void )
{
    double a, b, c, d;
    int except_flags;

    feclearexcept(FE_ALL_EXCEPT);
    a = 10;
    b = 2;
    c = scalbn(a, b);

    except_flags = fetestexcept(FE_ALL_EXCEPT);
    if(except_flags) {
        /* An error occurred; handle it appropriately. */
    }

    feclearexcept(FE_ALL_EXCEPT);

    d = sqrt(c/a);

    except_flags = fetestexcept(FE_ALL_EXCEPT);
    if(except_flags) {
        /* An error occurred; handle it appropriately. */
    }

    printf("Radix of machine's fp arithmetic is %f \n", d);
    printf("So %f = %f * (%f ^ %f) \n", c, a, d, b);

    return EXIT_SUCCESS;
}

produces the output:

Radix of machine's fp arithmetic is 2.000000
So 40.000000 = 10.000000 * (2.000000 ^ 2.000000)

Classification:

ANSI, POSIX 1003.1

Safety:
Cancellation point	No
Interrupt handler	No
Signal handler	No
Thread	Yes