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Target Machine

  • The target computer is a type of byte-addressable machine. It has 4 bytes to a word.
  • The target machine has n general purpose registers, R0, R1,...., Rn-1. It also has two-address instructions of the form:

Where, op is used as an op-code and source and destination are used as a data field.

  • It has the following op-codes:
      ADD (add source to destination)
        SUB (subtract source from destination)
        MOV (move source to destination)
  • The source and destination of an instruction can be specified by the combination of registers and memory location with address modes.
MODE FORM ADDRESS EXAMPLE ADDED COST
absolute M M Add R0, R1 1
register R R Add temp, R1 0
indexed c(R) C+ contents(R) ADD 100 (R2), R1 1
indirect register *R contents(R) ADD * 100 0
indirect indexed *c(R) contents(c+ contents(R)) (R2), R1 1
literal #c c ADD #3, R1 1
  • Here, cost 1 means that it occupies only one word of memory.
  • Each instruction has a cost of 1 plus added costs for the source and destination.
  • Instruction cost = 1 + cost is used for source and destination mode.

Example:

1. Move register to memory R0 → M

2. Indirect indexed mode:

3. Literal Mode:


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