#HW5.
#problem 1.
# You need 4 unsigned multiplications.
# And atleast 4 additions even you assume there is no carry out from the additions. 
# In reality,  carry out happens.
# the carry out brings other additions.
# The first program below is showing simple addition assuming no carry ont.
#
# The check routine exams carry out situation since MIPS additon ignore carry out.
# And set $v0 to 1 when carry out happends.
#
#      t1 t2
#   X  t3 t4
#--------------
#      t2*t4
#   t1*t4
#   t2*t3
#t1*t3
#-------------
#s1 s2 s3 s4



       .data
happy_msg:
        .asciiz "aaa"  #


        .text
        .globl main 
main:
        li $t1, 0x00000011
        li $t2, 0x00000011 #0x11111234
        li $t3, 0x00000011 #0x11111234
        li $t4, 0x11111234 
        multu  $t2,$t4
        mfhi   $s3
        mflo   $s4
        multu  $t1,$t4
        mfhi   $s2
        mflo   $t0
        add    $s3,$t0,$s3
        multu  $t2,$t3
        mflo   $t0
        add    $s3,$t0,$s3
        mfhi   $t0
        add    $s2,$t0,$s2
        multu  $t1,$t3
        mflo   $t0
        add    $s2,$t0,$s2
        mfhi   $t0
        add    $s1,$t0,$zero
     

CHECK:
        
        addi $sp, $sp,-20
        sw   $t7,0($sp)
        sw   $t8,4($sp)
        sw   $t9,8($sp)
        sw   $t6,12($sp)
        add  $v0,$zero,$zero
        add  $t7,$a0,$0
        add  $t8,$a1,$0
        add  $t9,$a2,$0
        srl  $t7,$t7,31
        srl  $t8,$t7,31
        and  $t6,$t7,$t8
        sne  $v0, $t6,$zero
        nop
        bne  $v0,$zero,RET  #set when both MSB = 1
        nop
        srl  $t9,$t9,31
        xor  $t6,$t7,$t8    # one of the MSB is 0 and the other is 1
        bne  $t6,$zero, EXAM
        nop
RET:    lw   $t7,0($sp)
        lw   $t8,4($sp)
        lw   $t9,8($sp)
        lw   $t6,12($sp)
        addi $sp, $sp,20
        j    $ra
        nop

EXAM:   xor  $t6,$t9,$t6
        beq  $t6,$zero,RET
        nop
        addi $v0,$zero,1
        j    RET
        nop






#Problem 2:  
# 2-1 
#         add r1,r2,r4  //divide into each field.  
#                000000 00010 00100 00001 00000    100000
#                       //combine for hex.
#        0000 0000 0100 0100 0000 1000 0010 0000
#         0x 00440820
#         addi r1,r2 0x 20
#         0x 20410020
#         nop
#         0x 00000000
#         beq   r0,r0,LOOP
#              to jump to LOOP you have to go - 3 instructions at non delayed branch
#               // nop(-1),  addi r1,r2,0x20 (-2) add r1,r2,r3 (-3) .
#         000100 00000 00000 ( -3 in binary which is 1111 1111 1111 1101)
#         so...0x1000fffd
#               to jump to LOOP you have to go - 4 instructions at delayed branch.
#              //nop(-1),  addi r1,r2,0x20 (-2) add r1,r2,r3 (-3)  beq r0,r0,LOOP(-4)
#         000100 00000 00000(-4 in binary)
#         so ..0x1000fffc
# 2-2     0x400000              j LINE1
#         0x400004              nop
#         0x400008              nop
#         0x40000c   LINE1:     beq r0,r0,LINE2
#
#                            j LINE1 becomes  j 0x40000c
#                              000010  0000 0100 0000 0000 0000 0000 11------00(drop 2 bits)
#                              0000   1000  0001 0000 0000 0000 0000 0011------
#                 j LINE1    0x 08100003
#                 nop        0x 00000000
#                 nop        0x 00000000
#         //for non delayed branch
#                            jump 2 instructions so,
#                beq r0,r0,LINE2             0x10000002
#         //for delayed branch   
#                            jump 1 instruction so,
#                            0x10000001
# 2-3    
#         bne r1,r2,3
#                    for non delayed branch,   jump 3 instructions from 0x400000(3* 4 = 12 =c)
#                so..0x40000c
#         bne r1,r2,-3   
#                    for non delayed branch, jump -3 instructions from 0x40000c (-3* 4 = -12 =-c)
#                so  0x400000

#Problem 3:

#Problem 4:
#                 r1 = 3
#                 r1 = 3 r2 = 5
#                 r1 = 3 r2 = 5 r3 =-2
#                 r1 = 3 r2 = 5 r3 =-2 r4 =-2               r31 = 0
#                                                           r31 = 0
#                 r1 = 10101  r2 = 5 r3 = -2                r31 = 0
#                 r1 = 10101  r2 = 5 r3 = -2                r31 = 0
#                 r1 = 10101  r2 = 5 r3 = -2 r4 = 0x2000    r31 = 0
#                 r1 = 10101  r2 = 5 r3 = -2 r4 = 0x2000    r31 = 0x1024
 

#Problem 5:
#   F F F F  
#Problem 6 :   
#     v0,v1: for return value
#     a0-a1: for argument passing
#     t0-t7: Temporary,not saved by callee
#     s0-s7: saved by callee