Lecture Notes: 04 Recipe for Assembly Code

Discuss the Homework #

• Pull it up on bottlenose
  • Write task in C
  • Then rewrite it in ASM
  • No compiler output
• Pull up solution directory
• Show calc running.

First: HW Questions #

• Homework questions?

Today: Assembly Recipie Examples #

Example 1: Collatz Conjecture #

• Start with an integer > 1.
• If even, divide by two.
• If odd, take 3*x+1.
• Iterate repeatedly

The conjecture:

• All integers > 1 eventually get you to one.

Our program will take an input on the command line and print the sequence to one and the number of iterations.

long
iterate(long x)
{
  if (x % 2 == 0) {
    return x/2;
  }
  else {
    return x*3 + 1;
  }
}

int
main(int argc, char* argv[])
{
  long x = atol(argv[1]);
  long i = 0; 
  
  while (x > 1) {
    printf("%ld\n", x);
    x = iterate(x);
    i++;
  }
  
  printf("i = %ld\n"):
  return 0;
}

Now, translate to ASM with the recipe.

Note patterns for “if” and “while” statements.

Example 2: Fives #

./fives.S

• Key point here: Dealing with individual characters in strings.

Bonus Examples: #

• Sum Array C => Sum Array ASM
• Linked List ASM