//----------------------------------------------------------------------
// euclidglobal.s
// Author: Bob Dondero
//----------------------------------------------------------------------

        .section .rodata

promptStr:
        .string "Enter an integer: "
        
scanfFormatStr:
        .string "%ld"
        
printfFormatStr:
        .string "The gcd is %ld\n"

//----------------------------------------------------------------------

        .section .data

//----------------------------------------------------------------------

        .section .bss

l1:
        .skip   8
l2:
        .skip   8
lGcd:
        .skip   8
lTemp:
        .skip   8
lAbsFirst:
        .skip   8
lAbsSecond:
        .skip   8
        
//----------------------------------------------------------------------

        .section .text

        //--------------------------------------------------------------
        // Assign to lGcd the greatest common divisor of l1 and l2.
        // void gcd(void)
        //--------------------------------------------------------------
        
        // Must be a multiple of 16
        .equ    GCD_STACK_BYTECOUNT, 16
        
gcd:

        // Prolog
        sub     sp, sp, GCD_STACK_BYTECOUNT
        str     x30, [sp]
         
        // lAbsFirst = labs(l1)
        adr     x0, l1
        ldr     x0, [x0]
        bl      labs
        adr     x1, lAbsFirst
        str     x0, [x1]

        // lAbsSecond = labs(l1)
        adr     x0, l2
        ldr     x0, [x0]
        bl      labs
        adr     x1, lAbsSecond
        str     x0, [x1]

gcdLoop:

        // if (lAbsSecond == 0) goto gcdLoopEnd
        adr     x0, lAbsSecond
        ldr     x0, [x0]
        cmp     x0, 0
        beq     gcdLoopEnd

        // lTemp = lAbsFirst % lAbsSecond
        // remainder = (dividend - (quotient * divisor))
        adr     x0, lAbsFirst
        ldr     x0, [x0]
        adr     x1, lAbsSecond
        ldr     x1, [x1]
        sdiv    x2, x0, x1
        mul     x3, x2, x1
        sub     x4, x0, x3
        adr     x0, lTemp
        str     x4, [x0]

        // lAbsFirst = lAbsSecond
        adr     x0, lAbsSecond
        ldr     x0, [x0]
        adr     x1, lAbsFirst
        str     x0, [x1]

        // lAbsSecond = lTemp
        adr     x0, lTemp
        ldr     x0, [x0]
        adr     x1, lAbsSecond
        str     x0, [x1]

        // goto gcdLoop
        b       gcdLoop

gcdLoopEnd:

        // lGcd = lAbsFirst
        adr     x0, lAbsFirst
        ldr     x0, [x0]
        adr     x1, lGcd
        str     x0, [x1]            
        
        // Epilog and return
        ldr     x30, [sp]
        add     sp, sp, GCD_STACK_BYTECOUNT
        ret

        .size   gcd, (. - gcd)
        
        //--------------------------------------------------------------
        // Read two integers from stdin. Compute their greatest common
        // divisor, and write it to stdout. Return 0.
        // int main(void)
        //--------------------------------------------------------------

        // Must be a multiple of 16
        .equ    MAIN_STACK_BYTECOUNT, 16

        .global main

main:

        // Prolog
        sub     sp, sp, MAIN_STACK_BYTECOUNT
        str     x30, [sp]
        
        // printf("Enter an integer: ")
        adr     x0, promptStr
        bl      printf

        // scanf("%ld", &l1)
        adr     x0, scanfFormatStr
        adr     x1, l1
        bl      scanf

        // printf("Enter an integer: ")
        adr     x0, promptStr
        bl      printf

        // scanf("%ld", &l2)
        adr     x0, scanfFormatStr
        adr     x1, l2
        bl      scanf

        // gcd()
        bl      gcd

        // printf("The gcd is %ld\n", lGcd)
        adr     x0, printfFormatStr
        adr     x1, lGcd
        ldr     x1, [x1]
        bl      printf
        
        // Epilog and return 0
        mov     w0, 0
        ldr     x30, [sp]
        add     sp, sp, MAIN_STACK_BYTECOUNT
        ret

        .size   main, (. - main)