# Add the numbers in an array
# C program:
# 
# sum = 0;
# for (i=0; i<5; i++)
#   sum = sum + a[i];
#  
#

# MARS has a unified memory for code and data, so both cannot start at address 0.
# However, our MIPS has distinct memories for both, and we need both to start at 0.
# Here's what I did:  Choose the "Compact, Text at 0" memory configuration, which
# puts data starting at address 0x2000.  Then, after compiling, manually edit the
# machine code to adjust all lw/sw memory references (adjusting the immediate
# downwards by 0x2000).



.data 0x2000
sum:    .space 4
i:      .space 4
a:      .word 7,8,9,10,8

.text 0x0000			# Be sure to set memory configuration Compact, Text at 0
main:
     sw    $0, 0x2000($0)       # sum = 0;
     sw    $0, 0x2004($0)       # for (i = 0;
     lw    $9, 0x2004($0)       # allocate register for i
     lw    $8, 0x2000($0)       # choose register $8 to hold value for sum
loop:
     sll   $10, $9, 2     	# covert "i" to word offset
     lw    $10, 0x2008($10)   	# load a[i]
     add   $8, $8, $10    	# sum = sum + a[i];
     sw    $8, 0x2000($0)       # update variable in memory
     addi  $9, $9, 1      	# for (...; ...; i++
     sw    $9, 0x2004($0)   	# update memory
     slti  $10, $9, 5     	# for (...; i<5;
     bne   $10, $0, loop
end: 
     j     end          	# infinite loop "trap" because we don't have syscalls to exit