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#CS2710 Homework 3
# Put your name here.
#
# Read these instructions carefully and fully.
#
# Write a MIPS assembly program that copies n values from array A to array B.
# The definitions of A and B are in the .data section below.
# The equivalent program in Java would be something like this:
# for(i=0; i<n; i++) B[i] = A[i];
# alternately, you can think of the equivalent Java while() loop:
# i=0;
# while(i<n) {
#   B[i] = A[i];
#   i++;
# }
# It doesn't much matter, since the assembler code for either approach
# would be pretty much the same.
#
# Your assembly program must implement a loop that uses appropriate branching 
# statements of the recent reading assignments and lectures.
# The number of iterations of the loop must be determined from
# the data value associated with the label n (below), so that you can change the
# number of iterations that your program executes simply by varying the
# value following the .word directive (and re-assembling/re-executing).
# Remember, you must load the value at n into a register of your choice
# in order to be able to do anything with it.
# 
# At the end of the program, unconditionally jump back to its beginning.
# Also: comment your program - every instruction should have one.
#
# Test/verify your program with the data value at n initialized to 5.
# When your loop finishes, and you unconditionally jump back to the start
# of the program, it should just run again (and again and again).
#
# Test again with the value at n initialized to 0 - the loop shouldn't
# execute at all, and no array values should be copied. But the program
# should run again and again when you unconditionally jump back to the start.
# 
# Next, set the .word at n to 15 and re-execute the program. 
# What happens when the first loop completes?
# What does a Java program do in a similar situation?
# What happens when you unconditionally jump back to the start of 
# the program after the first loop and it runs again? 
# Explain everything thoroughly with comments here. 
# 
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.text		# Optional, but .text tells the assembler that following this are program instructions

start:
	# i=0;
	addi	$t0, $zero, 0		#t0=0; (init loop counter)
	lw	$t1, n			#t1=value at address n (number of elements to copy from A to B
	
loop:	# while(i<n) {
	beq	$t0, $t1, end		#if(i==n) jump to end
	sll	$t3, $t0, 2		#compute array offset in bytes (t3=t0*4)
#   B[i] = A[i];
	lw	$t4, A($t3)		#load from A+offset
	sw	$t4, B($t3)		#store to B+offset
#   i++;
	addi	$t0, $t0, 1		#t0++ (increment counter)
	j	loop			#and repeat loop 
end:
	j	start			#repeat from start


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.data 		# Tells the assembler that the following directives affect the .data section of memory	
A:		# A represents an array of 9 32-bit words containing the values below
.word 1,2,3,4,5,6,7,8,9
B:		# B represents a second array of 5 32-bit words, all initialized to 0.
.word 0,0,0,0,0
n:		# n specifies the number of values to copy from A to B
.word 15