scalb()

Synopsis:

```#include <math.h>

double scalb( double x,
double 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:

This function computes x × rn, where r is the radix of the machine's floating point arithmetic and n is a finite number. When r is 2, scalb() is equivalent to ldexp().

Note: We recommend that you use scalbn() because it computes by manipulating exponents, instead of using mock multiplications or additions.

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

• Call feclearexcept(FE_ALL_EXCEPT) before calling scalb().
• On return, if fetestexcept(FE_ALL_EXCEPT) is nonzero, then an error has occurred.

Returns:

x * rn

If: These functions return: Errors:
n isn't an integer NaN FE_INVALID
x is Inf, and n is Inf Inf
x is Inf, and n isn't Inf NaN FE_INVALID
x isn't Inf, and n is Inf Inf, with the sign matching x
x isn't Inf, and n is -Inf 0.0, with the sign matching x
x or n is NaN NaN
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 = scalb(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:

Standard Unix; removed from POSIX.1-2008

Safety:
Cancellation point No
Interrupt handler No
Signal handler No