Consider the following code used to implement the instruction: foo $s0, $s1, $s2

mask: .word 0xfffff83f

start: lw $t0,mask($zero)

lw $s0,shifter($zero)

and $s0,$s0,$t0

andi $s2,$s2,0x1f

sll $s2,$s2,6

or $s0,$s0,$s2

sw $s0, shifter($zero)

shifter:sll $s0,$s1,0

Describe how it works. Why do you suppose that writing "self-modifying code" such as this is a bad idea (and often times not actually allowed)?