Fixed-Point Blockset

Bitwise Operator

Perform the specified bitwise operation on the inputs

Library

Bits

Description

The Bitwise Operator block is a masked S-function that performs the specified bitwise operation on its operands.

Unlike the logic operations performed by the Logical Operator block, bitwise operations treat the operands as a vector of bits rather than a single number. You select the bitwise Boolean operation with the Operator parameter list. The supported operations are given below.

Operation	Description
AND	TRUE if the corresponding bits are all TRUE
OR	TRUE if at least one of the corresponding bits is TRUE
NAND	TRUE if at least one of the corresponding bits is FALSE
NOR	TRUE if no corresponding bits are TRUE
XOR	TRUE if an odd number of corresponding bits are TRUE
NOT	TRUE if the input is FALSE (available only for single input)

Unlike the Simulink Bitwise Logical Operator block, the Bitwise Operator block does not support shift operations. Refer to Shifts to learn how to perform shift operations with the Fixed-Point Blockset.

The size of the output depends on the number of inputs, their vector size, and the selected operator:

• The NOT operator accepts only one input, which can be a scalar or a vector. If the input is a vector, the output is a vector of the same size containing the bitwise logical complements of the input vector elements.
• For a single vector input, the block applies the operation (except the NOT operator) to all elements of the vector. If a bit mask is not specified, then the output is a scalar. If a bit mask is specified, then the output is a vector.
• For two or more inputs, the block performs the operation between all of the inputs. If the inputs are vectors, the operation is performed between corresponding elements of the vectors to produce a vector output.

When configured as a multi-input XOR gate, this block performs an addition- modulo-two operation as mandated by the IEEE Standard for Logic Elements.

If the Use bit mask check box is not selected, then the block can accept multiple inputs. You select the number of input ports with the Number of input ports parameter. The input data types must be identical.

If the Use bit mask check box is selected, then a single input is associated with the bit mask you specify with the Bit Mask parameter. You specify the bit mask using any valid MATLAB expression. For example, you can specify the bit mask 00100101 as 2^5+2^2+2^0. Alternatively, you can use strings to specify a hexadecimal bit mask such as {'FE73','12AC'}. If the bit mask is larger than the input signal data type, then it is ignored.

Note    The output data type, which is inherited from the driving block, should represent zero exactly. Data types that satisfy this condition include signed and unsigned integers and any floating-point data type.

The Treat mask as parameter list controls how the mask is treated. The possible values are Real World Value and Stored Integer. In terms of the general encoding scheme described in Scaling, Real World Value treats the mask as V = SQ + B where S is the slope and B is the bias. Stored Integer treats the mask as a stored integer, Q. For more information about this parameter list, refer to the Gateway In block.

Remarks

You can use the bit mask to perform a bit set or a bit clear on the input. To perform a bit set, you configure the Operator parameter list to OR and create a bit mask with a 1 for each corresponding input bit that you want to set to 1. To perform a bit clear, you configure the Operator parameter list to AND and create a bit mask with a 0 for each corresponding input bit that you want to set to 0.

For example, suppose you want to perform a bit set on the fourth bit of an 8-bit input vector. The bit mask would be 00010000, which you can specify as 2^4 in the Bit mask parameter. To perform a bit clear, the bit mask would be 11101111, which you can specify as 2^7+2^6+2^5+2^3+2^2+2^1+2^0 in the Bit mask parameter.

Parameters and Dialog Box

Operator

The bitwise logical operator associated with the specified operands.

Use bit mask

Specify if the bit mask is used (single input only).

Number of input ports

The number of inputs.

Bit Mask

The bit mask to associate with a single input.

Treat mask as

Treat the mask as a real-world value or as an integer.

Conversions

The Bit Mask parameter is converted from a double to the input data type offline using round-to-nearest and saturation. Refer to Parameter Conversions for more information about parameter conversions.

Examples

To help you understand the Bitwise Operator block logic operations, consider the fixed-point model shown below.

The Constant blocks are configured to output an 8-bit unsigned integer (uint(8)). The results for all logic operations are shown below.

Operation	Binary Value	Decimal Value
AND	00101000	40
OR	11111101	253
NAND	11010111	215
NOR	00000010	2
XOR	11111000	248
NOT	N/A	N/A

Characteristics

Input Port	Any data type supported by the blockset
Output Port	Same as the input
Direct Feedthrough	No
Scalar Expansion	Of inputs

Bit Set

Compare To Constant