Midterm solutions

[Arrvindh Shriraman]

I will be going over these in class on Oct 30th.

For question D. Here is a mod.s that is runnable in venus. 

It replaces mod with a software routine that mimics it.

.globl main

.data

a: .string "happy"

b: .string "times"

init: .string "XXXXX" # 12 Xs

.text

# C : Cipher(char* str).

cipher:

     addi    s3,zero,25

loop_header:

lbu  s2, 0(a0) # Read character ch

beqz s2, end

addi s7,a0,0

    addi a0,a0,1

loop:

     addi s1, s2, -97 #

     bltu s3,s1,loop_header

     addi s2,s2,13

     lui     s4, 322639

  addi    s4, s4, -945

  mulhu   s4, s2, s4

  srli    s4, s4, 3

  addi    s5, zero, 26

  mul     s4, s4, s5

  sub     s2, s2, s4

    addi    s2,s2,97

     sb      s2, 0(a1)

     addi    a1,a1,1

     jal loop_header

end:

ret

main:

   la a0, a

   la a1,init

   jal cipher

   li a0,10

   ecall%