Legacy Document

scalb

You can use the scalb function to perform efficient scaling by a power of 2.

double_t scalb (double_t x, long int n);

x

Any floating-point number.

n

An integer representing a power of 2 by which x should be multiplied.

DESCRIPTION

The scalb function performs efficient scaling of its floating-point argument by a power of 2.

$scalb(x,n)\; =\; x\times 2n$

Using the scalb function is more efficient than performing the actual arithmetic.

This function performs the same operation as the ldexp transcendental function described on page 10-16.

EXCEPTIONS

When x is finite and nonzero, either the result of $scalb(x,n)$ is exact or it raises one of the following exceptions:

• inexact (if the result causes an overflow or underflow exception)
• overflow (if the result is outside the range of the data type)
• underflow (if the result is inexact and must be represented as a denormalized number or 0)

SPECIAL CASES

Table 10-12 shows the results when the floating-point argument to the scalb function is a zero, a NaN, or an Infinity. In this table, n is any integer.

Special cases for the scalb function

Operation	Result	Exceptions raised
$scalb(+0,n)$	+0	None
$scalb(-0,n)$	$-0$	None
$scalb(NaN,n)$	NaN	None[33]
$scalb(+$ ,n)	+	None
$scalb(-$ ,n)	$-$	None

EXAMPLES

z = scalb(1, 3);  /* z = 1  23 = 8 */

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[33] If the NaN is a signaling NaN, the invalid exception is raised.