Consider the following assembly program written for $32-$bit RISC:

ld r$20,16000$ # load immediate

ld r$19,20000$

ld r$18,40000$

start:

add r$3,$ r$20,$ r$19$

ld r$1,0($r$3)$ # load into r$1$ from memory

add r$4,$ r$20,$ r$18$

ld r$2,0($r$4)$

mult r$2,$ r$1,$ r$2$

st $0($r$4),$ r$2$ # store r$2$ into memory

ld r$2,4$

sub r$20,$ r$20,$ r$2$

bnez r$20,$ start # jump to start if r$20$ not equal with zero

a$)$ Write a C program that is equivalent to the given assembly program.

b$)$ Open the loop in assembly language up to $4$ iterations. Reduce the program by renaming registers as follows: Change it to minimize the number of stalls.