AdventOfCode/2017/23/23.md

## \-\-- Day 23: Coprocessor Conflagration \-\--

You decide to head directly to the CPU and fix the printer from there.
As you get close, you find an *experimental coprocessor* doing so much
work that the local programs are afraid it will [halt and catch
fire](https://en.wikipedia.org/wiki/Halt_and_Catch_Fire). This would
cause serious issues for the rest of the computer, so you head in and
see what you can do.

The code it\'s running seems to be a variant of the kind you saw
recently on that [tablet](18). The general functionality seems *very
similar*, but some of the instructions are different:

-   `set X Y` *sets* register `X` to the value of `Y`.
-   `sub X Y` *decreases* register `X` by the value of `Y`.
-   `mul X Y` sets register `X` to the result of *multiplying* the value
    contained in register `X` by the value of `Y`.
-   `jnz X Y` *jumps* with an offset of the value of `Y`, but only if
    the value of `X` is *not zero*. (An offset of `2` skips the next
    instruction, an offset of `-1` jumps to the previous instruction,
    and so on.)

The coprocessor is currently set to some kind of *debug mode*, which
allows for testing, but prevents it from doing any meaningful work.

If you run the program (your puzzle input), *how many times is the `mul`
instruction invoked?*

Your puzzle answer was `5929`.

## \-\-- Part Two \-\-- {#part2}

Now, it\'s time to fix the problem.

The *debug mode switch* is wired directly to register `a`. You [flip the
switch]{title="From 'magic' to 'more magic'."}, which makes *register
`a` now start at `1`* when the program is executed.

Immediately, the coprocessor begins to overheat. Whoever wrote this
program obviously didn\'t choose a very efficient implementation.
You\'ll need to *optimize the program* if it has any hope of completing
before Santa needs that printer working.

The coprocessor\'s ultimate goal is to determine the final value left in
register `h` once the program completes. Technically, if it had that\...
it wouldn\'t even need to run the program.

After setting register `a` to `1`, if the program were to run to
completion, *what value would be left in register `h`?*

Your puzzle answer was `907`.

Both parts of this puzzle are complete! They provide two gold stars:
\*\*

At this point, you should [return to your Advent calendar](/2017) and
try another puzzle.

If you still want to see it, you can [get your puzzle
input](23/input).