· Nov 23, 2017 4m read

Advent of Code 2016 Day23: Safe Cracking

This is a series of programming challenges for beginners and experienced Caché programmers.

For an introduction : go to article

Remember the assembunny language we had to code on day 12 (

There is a new instruction we have to implement which toggles an instruction x lines away (further or back).

  • For one-argument instructions, inc becomes dec, and all other one-argument instructions become inc.
  • For two-argument instructions, jnz becomes cpy, and all other two-instructions become jnz.
  • The arguments of a toggled instruction are not affected.
  • If an attempt is made to toggle an instruction outside the program, nothing happens.
  • If toggling produces an invalid instruction (like cpy 1 2) and an attempt is later made to execute that instruction, skip it instead.
  • If tgl toggles itself (for example, if a is 0tgl a would target itself and become inc a), the resulting instruction is not executed until the next time it is reached

Look for for the complete explanation.

So we can re-use much of the code we wrote on day 12.

Basically, I included the new instruction, and made the other instructions more robust (since now, we can have 'illegal' values which we need to ignore).

Here is the code i wrote (it is also worth looking in for the comment that Dmitry wrote about his transpiler of assembunny).

Class AOC2016.Day23 Extends AOC2016.Utils

ClassMethod Part(file As %String = "day23.txt", part As %Integer = 1)
  #Dim iInput, counter, next as %Integer
  #Dim input, instruction, instruction2, param1, param2 as %String
  #Dim var, register, line as %String

  For var="a","b","c","d" Set register(var) = 0
  set register("a") = $Select(part = 1:7,1:12)

  Try {
    Do ..Input(file, .input)
    Set iInput = 1
    set counter=0
    While iInput '> input {
      set counter=counter+1
      Set line = input(iInput)
      Set instruction=$Piece(line," ",1)
      Set param1=$Piece(line," ",2)
      Set param2=$Piece(line," ",3)
      If instruction = "cpy" {
        If $Data(register(param2)) Set register(param2)=$Select($Data(register(param1)):register(param1),1:param1)
elseIf instruction = "inc" {
        If $Data(register(param1)) Set register(param1) = register(param1) + 1
elseIf instruction = "dec" {
        If $Data(register(param1)) Set register(param1) = register(param1) - 1
elseIf instruction = "jnz" {
        If $Select($Data(register(param1)):register(param1),1:param1)'=0 {
          Set iInput = iInput + $S($Data(register(param2)):register(param2),1:param2) -1 //-1 since every loop will do +1 anyway
elseif instruction = "tgl" {
        set next=$Select($Data(register(param1)):register(param1),1:param1)+iInput
        If $Data(input(next)) {
          set instruction2=$Piece(input(next)," ",1)
          If instruction2 = "inc" {
            set instruction2="dec"
elseIf (instruction2="dec")!(instruction2="tgl") {
            set instruction2="inc"
elseIf (instruction2="jnz") {
            set instruction2="cpy"
elseIf (instruction2="cpy") {
            set instruction2="jnz"
          set $Piece(input(next)," ",1)=instruction2
      Set iInput = iInput + 1
      //For part 2 : so we can see why it is so much slower
      If (counter#1000000)=0 {
        zwrite register
        Write "#",iInput,!
  catch {
    Write "Error : ",$ZError,!
  Write "register a = ",register("a"),!



As you can see, I also included the code for part2, which needs another input for register a.

This causes a change in the flow of instructions which makes the whole process much slower. I show the contents of the registers to let you see what is going on.


Look here for all our solutions so far : and


Here is the list of all Advent of Code 2016 articles  :

1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25 

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