Verilog Operators
Operators perform an operation on one or more operands within an expression. An expression combines operands with appropriate operators to produce the desired functional expression.
1. Arithmetic Operators
For the FPGA, division and multiplication are very expensive, and sometimes we cannot synthesize division. If we use Z or X for values, the result is unknown. The operations treat the values as unsigned.
| Character | Operation performed | Example |
| + | Add | b + c = 11 |
| – | Subtrac | b – c = 9, -b=-10 |
| / | Divide | b / a = 2 |
| * | Multiply | a * b = 50 |
| % | Modulus | b % a = 0 |
2. Bitwise Operators
Each bit is operated, the result is the size of the largest operand, and the smaller operand is left extended with zeroes to the bigger operand’s size.
| Character | Operation performed | Example |
| ~ | Invert each bit | ~a = 3’b010 |
| & | And each bit | b & c = 3’b010 |
| | | Or each bit | a | b = 3’b111 |
| ^ | Xor each bit | a ^ b = 3’b011 |
| ^~ or ~^ | Xnor each bit | a ^~ b = 3’b100 |
3. Reduction Operators
These operators reduce the vectors to only one bit. If there are the characters z and x, the result can be a known value.
| Character | Operation performed | Example |
| & | And all bits | &a = 1’b0, &d = 1’b0 |
| ~& | Nand all bits | ~&a = 1’b1 |
| | | Or all bits | |a = 1’b1, |c = 1’bX |
| ~| | Nor all bits | ~|a= 1’b0 |
| ^ | Xor all bits | ^a = 1’b1 |
| ^~ or ~^ | Xnor all bits | ~^a = 1’b0 |
4. Relational Operators
These operators compare operands and results in a 1-bit scalar Boolean value. The case equality and inequality operators can be used for unknown or high impedance values (z or x), and if the two operands are unknown, the result is a 1.
| Character | Operation performed | Example |
| > | Greater than | a > b = 1’b0 |
| < | Smaller than | a < b = 1’b1 |
| >= | Greater than or equal | a >= d = 1’bX |
| <= | Smaller than or equal | a <= e = 1’bX |
| == | Equality | a == b = 1’b0 |
| != | Inequality | a != b = 1’b1 |
| === | Case equality | e === e = 1’b1 |
| !=== | Case inequality | a !== d = 1’b1 |
5. Logical Operators
These operators compare operands and results in a 1-bit scalar Boolean value.
| Character | Operation performed | Example |
| ! | Not true | !(a && b) = 1’b1 |
| && | Both expressions true | a && b = 1’b0 |
| || | One ore both expressions true | a || b = 1’b1 |
6. Shift Operators
These operators shift operands to the right or left, the size is kept constant, shifted bits are lost, and the vector is filled with zeroes.
| Character | Operation performed | Example |
| >> | Shift right | b >> 1 results 4?b010X |
| << | Shift left | a << 2 results 4?b1000 |
7. Assignment Operators
There are three assignment operators, each of which performs different tasks, and are used with different data types:
- assign (continuous assignment)
- <= (non-blocking assignment)
- = (blocking assignment)
8. Other Operators
These are operators used for condition testing and to create vectors.
| Character | Operation performed | Example |
| ?: | Conditions testing | test cond. ? if true do this or if not do this |
| {} | Concatenate | c = {a,b} = 8’101010×0 |
| {{}} | Replicate | {3{2’b10}}= 6’b101010 |
9. Operators Precedence
The order of the table tells what operation is made first. The first one has the highest priority. The () can be used to override the default.
| Operators precedence |
|---|
| +, -, !, ~ (Unary) |
| +,- (Binary) |
| <<, >> |
| <,>,<=,>= |
| ==, != |
| & |
| ^, ^~ or ~^ |
| | |
| && |
| || |
| ?: |