Problem 8 on Project Euler with x86 Assembly


The problem:


Find the greatest product of five consecutive digits in the 1000-digit number.

73167176531330624919225119674426574742355349194934
96983520312774506326239578318016984801869478851843
85861560789112949495459501737958331952853208805511
12540698747158523863050715693290963295227443043557
66896648950445244523161731856403098711121722383113
62229893423380308135336276614282806444486645238749
30358907296290491560440772390713810515859307960866
70172427121883998797908792274921901699720888093776
65727333001053367881220235421809751254540594752243
52584907711670556013604839586446706324415722155397
53697817977846174064955149290862569321978468622482
83972241375657056057490261407972968652414535100474
82166370484403199890008895243450658541227588666881
16427171479924442928230863465674813919123162824586
17866458359124566529476545682848912883142607690042
24219022671055626321111109370544217506941658960408
07198403850962455444362981230987879927244284909188
84580156166097919133875499200524063689912560717606
05886116467109405077541002256983155200055935729725
71636269561882670428252483600823257530420752963450

My solution:

.text 
.globl main

main:
  /*-enter stack frame-*/
  pushl %ebp
  movl %esp, %ebp

  /*-read first 5-*/
        movl $0, %edi
  loop1:
    cmp $5, %edi
    je endLoop1
    movl $3, %eax
    movl $0, %ebx
    movl $buffer, %ecx
    addl %edi, %ecx
    movl $1, %edx
    int $0x80
    addl $1, %edi
    jmp loop1
  endLoop1:

  /*-multiply first five, put result on esi-*/
  call multiply
  movl %eax, %esi

  /*-keep reading until the end and keeping max product-*/
  loop2:
    movl $3, %eax
                movl $0, %ebx
                movl $buffer2, %ecx
                movl $1, %edx
                int $0x80
    cmp $0, %eax
                je endLoop2
    movl $buffer2, %ecx
    movb (%ecx), %dl
    andl $0xFF, %edx
    cmp $10, %edx
    je directJump
    call moveChars
                movl $buffer, %ecx
    addl $4, %ecx
    movb %dl, (%ecx)
    call multiply
    cmp %esi, %eax 
    jg greater
    jmp loop2
    greater:
    movl %eax, %esi
    directJump:
    jmp loop2
  endLoop2:

  /*-print result-*/
  pushl %esi
  pushl $string2
  call printf

  /*-leave stack frame-*/
  movl %ebp, %esp
  popl %ebp  

  movl $0, %eax
  ret

moveChars:
  movl $buffer, %eax
  addl $1, %eax
  movl (%eax), %ebx
  subl $1, %eax
  movl %ebx, (%eax)
  ret

multiply:
  movl $buffer, %ebx
  movb (%ebx), %al
  andl $0xFF, %eax
  subl $48, %eax
  movl $4, %ecx
  multiplyLoop:
    cmp $0, %ecx
    je doneMultiplying
    addl $1, %ebx
    movb (%ebx), %dl
    andl $0xFF, %edx 
    subl $48, %edx
    imul %edx,%eax
    subl $1, %ecx
    jmp multiplyLoop
  doneMultiplying:
  ret  

.data
string2: .string "result=%dn"
buffer: .space 5  
buffer2: .space 1

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