Practical 3 questions
Name:
Section:
Name:
Section:
Read and perform the lab guide posted on the course website. Answer the questions in the lab guide as you get to them in the spaces below. Numbers in square brackets (e.g. []) indicate the point value of each question. The annotations in parentheses refer to the step of the lab guide.
Sum (p2)
-
[1] (2.1) Where are
main
,loop
,done
,N
andSum
located (i.e. what address)? Hint: Assemble and use Settings > Show Labels Window in the Execute view. -
[1] (2.4) How many instructions were actually executed? What is the final value of
Sum
? -
[2] (2.6) How many instructions does your modified program execute when
N
is equal to 5? Can this number be improved? If so, how? Hint: If your modified program executes 5 or more additional instructions, you can do better. -
[2] (2.7) Will your modified program work if
N
is less than 0? You do not need to make any additional modifications.
Swap (p3)
-
[1] (3.3) What is the value of max and maxindex at the end of the program?
-
[2] (3.4) Comment out
slli x10, x7, 2
and rerun the program. What happens? Why? -
[2] (3.7) If you repeatedly apply your modified program to the subarrays of
A
from 0 to \( N-i \) where \(i\) is the number of times you've applied your program, what is the final state ofA
? -
[2] (3.8) Like
p2.asm
this program doesn't work ifN
is equal to 0. It is brittle in other ways as well. For example, what happens if all of the elements are less than -1? Is there a more robust way to set the maximum value, instead of using the magic constant of -1?
Sort (p4)
-
[2] (4.11) If
SwapMaxWithLast
needed to return a value how would that be accomplished? -
[2] (4.12) What changes would you need to make if
SwapMaxWithLast
needed more than 8 arguments? -
[2] (4.13) What changes would you need to make if
SwapMaxWithLast
called another procedure? -
[2] (4.14) The code in
p4-loop.asm
works almost like a procedure. Describe the changes you would make to convert thep4-loop.asm
code into asort
procedure which is called and which in turn calls SwapMaxWithLast.
Fib
-
[3] (5.3)
fib
infib.asm
usess
registers to store bothn
andfib(n ? 1)
. Couldt
registers be used? Which would you choose? -
[2] (5.4) While calculating
fib(4)
, how many times isfib
called? -
[2] (5.5) In your
fib
code, you should have two internal calls tofib
. Set a breakpoint at the line AFTER the first internal call tofib
. Then, while calculatingfib(4)
, observe the state of the stack when the breakpoint is hit (e.g. when recursion using the firstjal fib
is complete). Then, draw the state of your stack on the next page. Draw the stack as a rectangle, indicate each stack frame, and what register and value is present in each word. -
[2(5.5) What happens if
fib
does not restore the return address before usingjalr x0, 0(ra)
?
Draw your stack here: