Operators

Logical Operators

• AND &&, OR ||, NOT !
• Evaluates to a single bit value (1-True, 0-False, X-Unknown)
• Any non-zero value means True
• Operation with Unknown(X) will result in Unknown(X)

Bitwise Operators

• AND (&)
• OR (|)
• XOR (^)
• NEGATION (~)
• XNOR (~^ or ^~)

Relational Operators

• AND (&)
• OR (|)
• XOR (^)
• NAND (~&)
• XNOR (~^ or ^~)
• NOR (~|)

Shift Operators

• Shift Right (>>)

• Shift Left (<<)

• and << are Logical Shift Operators

• and <<< are Arithmetic Shift Operators

• Result in same length as operand

a=5'b10100;
b=a<<<2;    //b == 5'b10000
c=a>>>2;    //c==5'b11101 ,vacated bit is filled with MSB if the left operand is signed
d=a<<2;    //d==5'b10000
e=a>>2;    //e==5'b00101

Concatenation Operators

• It is the joining together of bits resulting from two or more expressions within { }

• The concatenation operators are used to form a bit pattern by joining two or more expressions

• Operands must be sized

  reg a;
  req [2:0]b, c;
  reg [7:0]x, y, z;
  
  a = 1'b1; b = 3'b100; c = 3'b110;
  
  x = {a, b, c};            // x =01100110
  y = {b, 2'b01, a};        // y =00100011
  z = {x[1:0], b[2:1], c};  // z =01010110
  
  x = {{2{a}}, b, {2{c}}};  // x =11100110110
  

Relational Operators

• , >=, <, <=

• Evaluates to a single bit value 0 (False) or 1 (True)
• Operation with Unknown(X) will result in Unknown(X)

Equality

• Logical: ==, !=
• Case: ===, !== (not synthesizeable)

a=4'b1x0z; b = 4'b1x0z;

a == b // Evaluates to x
a != b // Evaluates to x
a === b // Evaluates to 1
a !== b // Evaluates to 0

Conditional Operators

• conditional_expression ? true_expression : false_expression;

Arithmetic Operators

• Multiplication [*]

• Add [+]

• Subtract [-]

• Division [/]

• Modulus [%]

• Expensive on gates

• Represent physical hardwares eg. add will represent adders gates

Points to be noted

integer i;
reg [15:0] a,z;

a = -4'd12;
z = a/3;        //evaluates to 21841
i = -12/3;      // i evaluates to -4
i = - 'd12/3;   // i evalautes to
                // (2^32 - 12)/3 = 1431655761

a = -12/3       // a evaluates to 65532
                // 65532 = 2's complement of -4

• Negative register values are stored as 2’s complement, but are treated by arithmetic operators as unsigned operands
• if no base specifier is used

References

• https://www.theoctetinstitute.com/content/verilog/arrays/