Question

Write an ARM assembly language program for Heap Sort.

Answer 1

/*

R0 address of string used with printf ti output %d

R4 address of numbers to sort

R5 current number to be compared

R6 offset index for outer loop through numbers

R7 offset index for inner loop

R8 current smallest identified value

R9 current offset index of next uncompared value

*/

.global main

main:

  push {ip, lr}

  MOV R6, #0 @outerloop offset to numbers to be sorted

  MOV R7, #0 @innerloop offers to number to be sorted

  MOV R9, #0 @init value for index to next uncompared value

outerLoop:

  MOV R8, #99 @reset large default for next loop comparison

  MOV R7,R6 @copy outerloop offset to next starting offset for the innerloop

innerLoop:

  LDR R0, =output @load addr of output string

  LDR R4, =nums @load addr of nums to compare to R4

  LDR R5,[R4,R7] @load current num to R5 from R4 with offset R7

  MOV R1,R5 @move num for output

  BL printf

  CMP R5,R8 @is current < smallest so far

  BLT swapSmallest @if true, swap smallest to current first position then continue

continue:

  CMP R7,#16 @ 0 plus 4*4bytes for 5 entries in array

  ADD R7, R7,#4 @inc offset by 4 bytes

  BLT innerLoop

continueOuterLoop:

  CMP R6, #16 @check if we've looped through all values

  ADD R6, R6, #4

BLT outerLoop @if not, branch back to start of outer loop

_exit:

  POP {ip, lr}

resetLoopOffsets:

  MOV R7, #0 @reset loop counter

writeFinalSoredList: @TODO: this is a near copy of the innner loop - refactor this to function

  LDR R0, =writeSorted @load addr of output string

  LDR R4, =nums @load addr of nums

  LDR R5,[R4,R7] @load current num to R5 from R4 with offset R7

  MOV R1,R5 @move num for output

  BL printf

  CMP R7,#16 @ 0 plus 4*4bytes for 5 entries in array

  ADD R7, R7,#4 @inc offset by 4 bytes

  BLT writeFinalSoredList

doExit:

  MOV R1, #0

  MOV R7, #1

  SWI 0

swapSmallest:

  MOV R8,R5 @keep copy of smallest in the current loop

  LDR R10, [R4,R6] @tmp copy first position to R10

  LDR R11, [R4,R7] @tmp copy value in position currently being compared

  STR R10, [R4, +R7] @swap first position value to current position being compared

  STR R11, [R4, +R6] @swap the current smallest value into the current first position

  BX lr @return

.data

nums:

.word 5,2,7,1,8

output:

.asciz "%d\n"

writeSorted:

.asciz "%d\n"