--- /dev/null
+#!/usr/bin/perl -w
+
+use v5.36;
+use strict;
+
+my @code;
+my @regs = ((0) x 6);
+my $ip_reg;
+
+while(<STDIN>) {
+ if (/\A#ip (\d+)/) {
+ $ip_reg = $1;
+ next;
+ }
+ chomp;
+ push @code, [ split /\s+/ ];
+}
+
+my $nmachines = shift @ARGV;
+my @machines;
+# push @machines, [ ($_, ((0) x 6)) ] for 0 .. $nmachines;
+push @machines, [ (10961197, ((0) x 6)) ];
+
+my %seen;
+
+sub one_step($regs) {
+ my $ip = $regs->[6];
+ my ($op, $a, $b, $c) = @{ $code[$ip] };
+
+ $regs->[$ip_reg] = $ip;
+
+ if ($op eq 'addr') {
+ $regs->[$c] = $regs->[$a] + $regs->[$b];
+ } elsif ($op eq 'addi') {
+ $regs->[$c] = $regs->[$a] + $b;
+ } elsif ($op eq 'mulr') {
+ $regs->[$c] = $regs->[$a] * $regs->[$b];
+ } elsif ($op eq 'muli') {
+ $regs->[$c] = $regs->[$a] * $b;
+ } elsif ($op eq 'banr') {
+ $regs->[$c] = $regs->[$a] & $regs->[$b];
+ } elsif ($op eq 'bani') {
+ $regs->[$c] = $regs->[$a] & $b;
+ } elsif ($op eq 'borr') {
+ $regs->[$c] = $regs->[$a] | $regs->[$b];
+ } elsif ($op eq 'bori') {
+ $regs->[$c] = $regs->[$a] | $b;
+ } elsif ($op eq 'setr') {
+ $regs->[$c] = $regs->[$a];
+ } elsif ($op eq 'seti') {
+ $regs->[$c] = $a;
+ } elsif ($op eq 'gtrr') {
+ $regs->[$c] = $regs->[$a] > $regs->[$b] ? 1 : 0;
+ } elsif ($op eq 'gtir') {
+ $regs->[$c] = $a > $regs->[$b] ? 1 : 0;
+ } elsif ($op eq 'eqrr') {
+ $regs->[$c] = $regs->[$a] == $regs->[$b] ? 1 : 0;
+ } elsif ($op eq 'eqri') {
+ $regs->[$c] = $regs->[$a] == $b ? 1 : 0;
+ } elsif ($op eq 'nop') {
+
+ } else {
+ die "Unknown op $ op at $ip";
+ }
+ say join(' ', @{ $code[$ip] }, "\t", @$regs);
+ # $regs->[3] = $ARGV[0] if $ip == 35;
+ $regs->[6] = $regs->[$ip_reg] + 1;
+
+# if ($seen{join(',', @$regs)}++) {
+# say "seen";
+# $regs->[6] = -1;
+# return 0;
+# }
+ if ($regs->[6] >= @code) {
+ say "halts";
+ return 1;
+ } else {
+ return undef;
+ }
+}
+
+my $step = 0;
+while (1) {
+ say "step ", ++$step;
+ for my $m (0 .. $#machines) {
+ next if $machines[$m]->[6] == -1;
+ # say "machine $m";
+ if (one_step($machines[$m])) {
+ say "Machine $m halts after ste $step";
+ exit 0;
+ }
+ }
+}
+