Assignment 8, due Mar 27
On every assignment, write your name legibly as it appears on your University ID card! Homework is due on paper at the start of class on the day indicated (usually Friday). Exceptions will be made only by advance arrangement (excepting "acts of God"). Late work must be turned in to the TA's mailbox (ask the CS receptionist in 14 MLH for help). Never push homework under someone's door!
LIS R3,1 TESTR R4 BZS DONE LOOP: SL R3,1 ADDSI R4,-1 BZR LOOP DONE:
Here is a clever alternative solution:
LIS R3,1 BITTST R4,0 BBR SKIP0 SL R3,1 SKIP0: BITTST R4,1 BBR SKIP1 SL R3,2 SKIP1: BITTST R4,2 BBR SKIP2 SL R3,4 SKIP2: BITTST R4,3 BBR SKIP3 SL R3,8 SKIP3: BITTST R4,4 BBR SKIP4 SL R3,16 SKIP4:
a) Assuming all instructions take the same amount of time, what is the smallest shift count (in R4) for which the clever alternative is faster? (0.4 points)
b) Under the same assumptions, what is the largest shift count (in R4) for which the simple iterative solution is faster? (0.4 points)
c) How many shift (or shift-add) instructions are included in the clever alternative solution? (Hint: You will probably have to look things up in the Hawk manual to find out which of the instructions are shift instructions. (0.2 points)
Give the fastest Hawk code you can to multiply by 2015. (1.0 points)
A problem: Modify this code so it returns the low 32 bits of the product in R3 and the high 32 bits of the product in R4. (1.0 points)
Hint: Study how to do 64-bit shifts, a subject discussed in the section on Division in Chapter 9 of the notes and also in Section 10 of the Hawk manual. You should also look at which bits of R4 contain useful information as TIMESUL performs successive iterations.