ntuck@neu

./04-asm-recipe/notes.md

Rant: Efficient Workflows

  • Pull up cookie clicker.
  • Point out that the efficient strategy is to get upgrades ASAP, whether they're linear or mutiplicative.

Example upgrades for programming:

  • Touch typing.
    • Save some time typing.
    • Save getting distracted to find a key.
  • Getting an editor with automatic indentation and syntax highlighting.
    • Syntax highlighting automatically catches many syntax errors, saving a whole try-to-compile and then debug cycle each time.
  • Getting a keyboard-focused editor and learning the keybindings.
    • In vim, swapping two lines is 3 keystrokes.
  • Becoming familiar with the libraries you're using.
    • Especially the standard library for your language.
    • How do you convert a string to a long in C?
    • Autocompletion doesn't replace this.
  • Learn your environment's debugger in some detail. For us, that's GDB.
  • You'll see more upgrade opportunities. I suggest prioritizing them, even if it costs some time right now, even if you're not sure it's an upgrade.

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

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

Bonus Examples:

  • Sum Array
  • Linked List