MAL Code

We are using a simulator to understand how MIPS assembly language works. This has both good and bad aspects.

GOOD.

MIPS assembly language (and in fact any assembly languge) does not have I/O instructions. Our simulator eases our programming by making it appear as if there are the 3 I/O instructions putc, puts, and getc.
We cannot crash or otherwise mangle a real machine by directly running our assembly language programs.

BAD.

The simulator does not issue assembler errors for several common improper instructions! Instead, it quietly translates these instructions into proper ones.

Branch instructions in MAL must take operands (the ones for comparison) from registers. Only registers. Therefore, the instruction

    beq $10, 12, somewhere

is not a legal MIPS assembly language instruction. The simulator quietly puts the value 12 into a register (Which one? Try it and see!) and then does a proper beq instruction.

Karen does not even remember what the simulator does if code appears as

  .data
X:  .word 12

  .text
    beq $10, X, somewhere

This code does not generate an error as far as assembly is concerned. What Karen does not remember is whether the simulator assumes that the comparison is with the address assigned for variable X or with the contents of variable X (12).