#Poorak Mody Lab-4
 	.data
	#---------strings tobe used in the program-------
promptx:  .asciiz "\n\nEnter x: "
divsans:  .asciiz "\n the largest power of 2 that x is divisible by is: "
nds:	  .asciiz "\n not divisible by a power of 2"
promptn:  .asciiz "\n\nEnter n: "
ans: 	  .asciiz "\n n!="
anshi:    .asciiz "\n n!(highword)= "
anslo:	  .asciiz "\n n!(lowword) = "
	.text


main:
	#------calling part of 6.3-----	
	li $v0, 4		#load sys code for printing strings
	la $a0, promptx		#load address of string to be printed
	syscall			#prints the string
	li $v0, 5		#load sys code for reading ints
	syscall			#reads it
	move $a0,$v0		#copies $v0 to $a0
	beq  $a0,$zero,nd 	#checks if a0 is zero
	jal  divs		#jumps & links to procedure divs
	move $t1,$v0		#copies result of divs into $t1
	beq $t1,$zero,nd	#branches to nd when x=0
	li $v0, 4		#sys code for printing strings
	la $a0, divsans		#load address of string to be printed
	syscall			#prints the string
	li $v0,1		#load sys code for printing ints
	move $a0,$t1		#a0=t1
	syscall			#prints the int
	j part2a		#jump to part 2
	
#---(prob 6.3)divs checks the power of 2 that x is divisible by

divs:
	move $t0,$zero 		#setting t0 to zero
	move $v0,$zero 		#setting $v0 to zero

	loop:
		add $v0,$t0,$zero	#copy $t0 -> $v0
		and $t1,$a0,1		#and x with 1
		beq $t1,1,donelp	#branches to donelp if x AND 1 holds true
		addi $t0,$t0,1		#increments $t0 by 1
		srl  $a0,$a0,1		#shift register right by one bit(unsigned)
		j loop			#repeat 
	donelp:
		jr $ra		#return to calling part of main
	nd:
		li $v0, 4	#sys code for printing strings
		la $a0, nds	#load address of string to be printed
		syscall		#prints the string

#---(prob 6.8 a)fact calculates n!---------------------------	

part2a:
	li $v0,4		#load sys code for printing string
	la $a0,promptn 		#string to be printed
	syscall 		#prompt for n
	li $v0, 5		#load sys code for reading ints
	syscall			#reads it
	move $a0,$v0		#copies $v0 to $a0
	jal fact		#branch and link to fact
	move $t2,$v0		#copy value in $v0 into $t2
	li $v0, 4		#load system code forprinting strings
	la $a0,ans		#load string
	syscall			#print string
	li $v0,1		#load sys code for printing ints
	move $a0,$t2		#load value of int to be printed
	syscall			#print int (n!)
	j part2b		#branch to part2 b
	
fact:
	li $t1,1		#loads 1 into $t1
	bgt $a0,$t1,factcc	#branches to factcc if n>1
	li $v0,1		#returns n
	jr $ra
	
factcc:
	addi $sp,$sp,-4
	sw $ra,0($sp) 		#holdig $ra for later
	addi $sp, $sp, -4 	#move stack pointer
	sw $a0, 0($sp) 		#store n on stack
	addi $a0, $a0, -1 	#n-1
	jal fact 		#(recursion) calls fact(n-1)
	lw $ra,4($sp) 		#bringing back $ra
	lw $t1,0($sp) 		#bringing back n
	addi $sp, $sp,8		#resetting the stack pointer
	mul $v0,$v0,$t1		# $v0 = $v0*n
	jr $ra			#return to calling part of part2a

#---(prob 6.8 b)factdw calculates n! and result is a double word-------------------	
part2b:
	li $v0,4		#load sys code for printing string
	la $a0,promptn 		#string to be printed
	syscall 		#prompt for n
	li $v0, 5		#load sys code for reading ints
	syscall			#reads it
	move $a0,$v0		#copies $v0 to $a0
	li $v1,1		#initilize
	li $v0,0
	jal factdw		#branch and link to fact
	move $t2,$v0		#copy value in $v0 into $t2
	move $t6,$v1
	li $v0, 4		#load system code forprinting strings
	la $a0,anshi		#load string
	syscall			#print string
	li $v0,1		#load sys code for printing ints
	move $a0,$t2		#load value of int to be printed
	syscall			#print int (n!)hi
	
	li $v0, 4		#load system code forprinting strings
	la $a0,anslo		#load string
	syscall			#print string
	li $v0,1		#load sys code for printing ints
	move $a0,$t6			#load value of int to be printed
	syscall			#print int (n!)lo
	j end			#end program
	
factdw:
	li $t1,0		#loads 1 into $t1
	bgt $a0,$t1,factdwcc	#branches to factcc if n>0
	li $v1,1		#returns n
	li $v0,0
	jr $ra
	
factdwcc:
	addi $sp,$sp,-4
	sw $ra,0($sp) 		#holdig $ra for later
	addi $sp, $sp, -4 	#move stack pointer
	sw $a0, 0($sp) 		#store n on stack
	addi $a0, $a0, -1 	#n-1
	jal factdw 		#(recursion) calls fact(n-1)
	lw $ra,4($sp) 		#bringing back $ra
	lw $t1,0($sp) 		#bringing back n
	addi $sp, $sp,8		#resetting the stack pointer
	mult $v0,$t1		# $v0*n
	mflo $t3		# store low of vo*n in t3
	mult $v1,$t1		# $v1*n
	mflo $t5		# store low of v1*n in t5
	mfhi $t4		# store hi of v1*n in t4
	add $v0,$t4,$t3		#store in v0 the hi(n*v1)+lo(n*v0)
	move $v1,$t5		#store in v1 the lo(n*v1)
	jr $ra			#return to calling part of part2a
end:

#-----------------THE END------------------------------------