Day 4

2.7 Instructions for making Decisions

• MIPS has two instructions for making decisions

  • Using a value in our program to determine program flow.

• Branch Equal

  • Let’s us compare two items, and if they are equal move to a defined location.

  • MIPS instruction: beq $s0,$s1,label

  • if ($s0 == $s1)

    • goto Label

• Branch Not Equal

  • Compare two values and look for inequality.

  • MIPs instruction: bne $s0,$s,label

  • if ($s0 ≠ $s1)

    • goto label

• Jump

  • unconditional goto label

  • j label X

• Labels named, defined locations

  • in our programs or memory

• HL (High Level) Code:

  • if (i == j)

    • (i&j are $s3 & $s4)

      • f = g+h

        • f = $s0, g=$s1, h= $s2

  • Assumptions:

    • f-g in $s0-$s4

    • Want the code to “flow” the same

  • MIPS Code:

    • bne $s3, $s4, else

    • ad $s0,$s1,$s2

    • j EXIT

    • else

    • sub $s0,$s1, $s2

    • EXIT