Example Program

Here is an example using the lw and sw instructions. The program starts out by loading data into several registers. Notice that the load delay slots of the load instructions are filled with useful instructions. This is possible because the data is not used until several instructions after each load. For example, the value for x is not used until four instructions later, so the lw that loads it has its load delay slot filled with a useful instruction.

The nop (no-operation) instructions are used to follow the rule that a mult instruction should not be started until two instructions after a mflo or mfhi instruction. (Usually our SPIM programs do not follow this rule because SPIM does not emulate that aspect of MIPS.)

## pseudoPoly.asm
## evaluate the polynomial ax2 + bx + c
##
        .text
        .globl  main

main:
        lw   $t3,x          # get x
        lw   $t0,a          # get a
        lw   $t1,bb         # get bb
        lw   $t2,c          # get c

        mult $t3,$t3        # x2
        mflo $t4            # $t4 = x2
        nop
        nop
        mult $t4,$t0        # low  = ax2
        mflo $t4            # $t4  = ax2
        nop
        nop

        mult $t1,$t3        # low  = bx
        mflo $t5            # $t5  = bx
        addu $t5,$t4,$t5    # $t5  = ax2 + bx

        addu $t5,$t5,$t2    # $t5 = ax2 + bx + c
        sw   $t5,value      # value = polynomial

        .data
x:      .word   4 
value:  .word   1 
a:      .word  20
bb:     .word  -2           # the SPIM assembler does not allow the label "b"
c:      .word   5
 

This is a straightforward evaluation of the polynomial. By using Horner's method, and by cleverly filling some of the no-ops with instructions, the program could be greatly improved.