Using a Hardware Description Language - Digital Design of Signal Processing Systems: A Practical Approach - page 38

Example 2.6
Apply the & reduction operator to a 4-bit number A ¼ 4 0 b1011 :

assign out = &A;

This operation is equivalent to performing a bitwise & operation on all the bits of A :

out = A[0] & A[1] & A[2] & A[3];

2.6.3.8 Bitwise Arithmetic Operators

Bitwise arithmetic operators are also common to software programmers. These operators perform
bitwise operations on all the corresponding bits of the two operands. Table 2.11 gives all the bitwise
operators in Verilog.

Example 2.7

This example performs bitwise | operation on two 4-bit numbers A ¼ 4 0 b1011 and
B ¼ 4 0 b0011 . The Verilog expression computes a 4-bit C :

assign C = A | B;

performs the OR operation on corresponding bits of A and B and the operation is equivalent to:

C[0] = A[0] | B[0]
C[1] = A[1] | B[1]
C[2] = A[2] | B[2]
C[3] = A[3] | B[3]

2.6.3.9 Equality Operators

Equality operators are common to software programmers, but Verilog offers two flavors that are
specific to HW design: case equality ( ). A simple equality operator

( ¼¼ ) checks whether all the bits of the two operands are the same. If any operand has an x or z as one
of its bits, the answer to the equality will be x . The

¼¼¼ ) and case inequality (! ¼¼

as it also
matches x with x and z with z . The result of this operator is always a 0 or a 1 . There is a similar
difference between !

¼¼¼ operator is different from ¼¼

¼ and ! ¼¼ . The following example differentiates the two operators.

Table 2.11 Bitwise arithmetic operators

Operator type Operator symbol Operation performed

Bitwise Bitwise negation

& Bitwise AND

& Bitwise NAND

| Bitwise OR

| Bitwise NOR

^ Bitwise XOR

^ or ^ Bitwise XNOR