Documentation

pow2

Efficient fixed-point multiplication by 2K

b = pow2(a,K)

Description

b = pow2(a,K) returns the value of a shifted by K bits where K is an integer and a and b are fi objects. The output b always has the same word length and fraction length as the input a.

Note

In fixed-point arithmetic, shifting by K bits is equivalent to, and more efficient than, computing b = a*2k.

If K is a non-integer, the pow2 function will round it to floor before performing the calculation.

The scaling of a must be equivalent to binary point-only scaling; in other words, it must have a power of 2 slope and a bias of 0.

a can be real or complex. If a is complex, pow2 operates on both the real and complex portions of a.

The pow2 function obeys the OverflowAction and RoundingMethod properties associated with a. If obeying the RoundingMethod property associated with a is not important, try using the bitshift function.

The pow2 function does not support fi objects of data type Boolean.

The function also does not support the syntax b = pow2(a) when a is a fi object.

Examples

Example 4. Example 1

In the following example, a is a real-valued fi object, and K is a positive integer.

The pow2 function shifts the bits of a 3 places to the left, effectively multiplying a by 23.

a = fi(pi,1,16,8)
b = pow2(a,3)
binary_a = bin(a)
binary_b = bin(b)

MATLAB® returns:

a =

3.1406

DataTypeMode: Fixed-point: binary point scaling
Signedness: Signed
WordLength: 16
FractionLength: 8

b =

25.1250

DataTypeMode: Fixed-point: binary point scaling
Signedness: Signed
WordLength: 16
FractionLength: 8

binary_a =

0000001100100100

binary_b =

0001100100100000
Example 5. Example 2

In the following example, a is a real-valued fi object, and K is a negative integer.

The pow2 function shifts the bits of a 4 places to the right, effectively multiplying a by 2–4.

a = fi(pi,1,16,8)
b = pow2(a,-4)
binary_a = bin(a)
binary_b = bin(b)

MATLAB returns:

a =

3.1406

DataTypeMode: Fixed-point: binary point scaling
Signedness: Signed
WordLength: 16
FractionLength: 8

b =

0.1953

DataTypeMode: Fixed-point: binary point scaling
Signedness: Signed
WordLength: 16
FractionLength: 8

binary_a =

0000001100100100

binary_b =

0000000000110010
Example 6. Example 3

The following example shows the use of pow2 with a complex fi object:

format long g
P = fipref('NumericTypeDisplay', 'short');
a = fi(57 - 2i, 1, 16, 8)

a =
57 -                     2i
s16,8

pow2(a, 2)

ans =
127.99609375 -                     8i
s16,8

Extended Capabilities

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