Arithmetic Expression Algorithm

The genarith input is a tree (operand or operator):

• Operand (leaf node): id or number
  1. Get a register of the right kind (integer, real)

  2. An operand may be a variable or constant:
     1. Variable: Generate an instruction to load the variable into the register.

     2. Constant:
        1. Small constant: Generate an immediate instruction to load it into the register directly.

        2. Otherwise, make a literal for the value of the constant. Generate an instruction to load the literal into the register.
  3. Return the register number.

• Operator (interior node):
  1. Recursively generate code to put each operand into a register.

  2. Generate the operation on these registers, producing a result in one of the source registers.

  3. Mark the other source register unused.

  4. Return the result register number.