//
//  Program file used to demo writing the function "sumRange"
//

/* --------------------------------------------------
   Define required labels for EGTAPI
   -------------------------------------------------- */
.global main, Stop, CodeEnd, DataStart, DataEnd

.global Pause, sumRange

/* --------------------------------------------------
   Begin of the program instructions
   -------------------------------------------------- */
.text
main:
//  sum = sumRange(A, a, b): 

	// pass b
	movw r0, #:lower16:b
	movt r0, #:upper16:b
	ldr  r0, [r0]
	push {r0}

	// pass a
        movw r0, #:lower16:a
        movt r0, #:upper16:a
        ldr  r0, [r0]
        push {r0}

	// pass A
        movw r0, #:lower16:A
        movt r0, #:upper16:A	// r0 = base of array A
        push {r0}

	bl sumRange

	add sp, sp, #12

        movw r1, #:lower16:sum
        movt r1, #:upper16:sum
	str  r0, [r1]

Pause:
//  sum = sumRange(B, 2, 4): 

        // pass 4
        mov  r0, #4
        push {r0}

        // pass 2
	mov  r0, #2
        push {r0}

        // pass B
        movw r0, #:lower16:B
        movt r0, #:upper16:B    // r0 = base of array B
        push {r0}

        bl sumRange

        add sp, sp, #12

        movw r1, #:lower16:sum
        movt r1, #:upper16:sum
        str  r0, [r1]


Stop:
nop			   // Stop point of main( )

sumRange:	// sumRange(A, a, b):
		// return value is in register r0
// Prelude
	push {lr}
	push {fp}
	mov  fp, sp
	sub  sp, sp, #8

// body
	mov  r0, #0
	str  r0, [fp,#-4]	// s = 0

	ldr  r0, [fp, #12]
	str  r0, [fp, #-8]	// i = a

while:  // while (i < b)

        //// Get i into r0
        ldr     r0, [fp, #-8]   // offset(local var i) = -8 from FP

        //// Get b into r1
        ldr     r1, [fp, #16]   // offset(b) = 16 from FP

        //// Check for (i < b)
        cmp     r0, r1          // r0 = i, r1 = b
        bge     whileEnd        // Exit while loop if FALSE

        // s = s + A[i];

        ///// get A[i] into r10
        ldr     r0, [fp, #8]    // r0 = addr of array A

        ldr     r1, [fp, #-8]   // r1 = i
        add     r1, r1, r1      // r1 = 2*i
        add     r1, r1, r1      // r1 = 4*i   = offset used to access A[i]

        ldr     r10, [r0, r1]   // r10 = A[i] (r0=A(base), r1=offset)

        ///// get s into r0
        ldr     r0, [fp, #-4]   // r0 = s

        ///// compute s + A[i]
        add     r0, r0, r10     // r0 = s + A[i]

        ///// Save sum in memory variable s
        str     r0, [fp, #-4]   // s = s + A[i]

        // i++
        ldr     r0, [fp, #-8]   // r0 = i
        add     r0, r0, #1      // r0 = i+1
        str     r0, [fp, #-8]   // i = i+1

        b       while           // End of while body - loop back !!

whileEnd:

        // return(s)

        //// Put the return value in the agreed register (r0)
        ldr     r0, [fp, #-4]   // r0=s

        /* =============================================================
           Function Postlude: de-allocate local variable and restore FP
           ============================================================= */
        mov     sp, fp          // De-allocate local variables
        pop     {fp}            // Restore fp
        pop     {pc}            // Return to the caller

// postlude
	mov sp, fp
	pop {fp}
	pop {pc}

CodeEnd:
nop

/* --------------------------------------------------
   Begin of the permanent program variables
   -------------------------------------------------- */
.data
DataStart:

A:	.4byte	11, 12, 13, 14, 15, 16, 17, 18, 19 , 20
B:	.4byte	1,   2,  3,  4,  5,  6,  7,  8,  9 , 10
a:	.4byte	1
b:	.4byte	3
sum:	.skip   4

DataEnd:

.end