solution.php

#!/usr/bin/env php
<?php
include("common.php");
$lines = read_input();
$program = []; $ipidx =0; $cpustate = [0,0,0, 0,0,0];
if(isset($argv[2]))$cpustate[0]=(int)$argv[2];
$c=0;
foreach($lines as $line){
    [$cmd,$_rest] = explode(' ', $line);
    $args = array_pad( line2digits($line), 3, 0);
    if($cmd === '#ip'){ $ipidx = $args[0]; continue; }
    $program[$c] = array_merge([$cmd], $args);
    $c++;
}
//printf("ipidx: %d\n",$ipidx); $programsize = count($program)-1; for($i=0;$i<=$programsize;$i++)printf("I: %-3d CMD: %s\n",$i, state2string($program[$i]));

function simulateProgram(array $program, int $ipidx, array $cpustate ): array {
    $programsize = count($program)-1;
    $c=0; while(true){
        $ip  = $cpustate[ $ipidx ];
        if( $ip > $programsize ) {
            printf("--->CPU at step: %-3d %s | IP: %-4d \n", $c, state2string($cpustate), $ip);
            printf("--->IP > programsize: %d . Terminating...\n", $programsize);
            break;
        }
        $ins = $program[ $ip ];
        //printf("CPU at step: %-9d %s | IP: %-4d | INS: %15s\n", $c, state2string($cpustate), $ip, ve($ins));
        switch($ins[0]){
         case "addr":$cpustate[$ins[3]] = $cpustate[ $ins[1] ] + $cpustate[ $ins[2] ];    break;
         case "addi":$cpustate[$ins[3]] = $cpustate[ $ins[1] ] + $ins[2];                 break;
         case "mulr":$cpustate[$ins[3]] = $cpustate[ $ins[1] ] * $cpustate[ $ins[2] ];    break;
         case "muli":$cpustate[$ins[3]] = $cpustate[ $ins[1] ] * $ins[2];                 break;
         case "banr":$cpustate[$ins[3]] = $cpustate[ $ins[1] ] & $cpustate[ $ins[2] ];    break;
         case "bani":$cpustate[$ins[3]] = $cpustate[ $ins[1] ] & $ins[2];                 break;
         case "borr":$cpustate[$ins[3]] = $cpustate[ $ins[1] ] | $cpustate[ $ins[2] ];    break;
         case "bori":$cpustate[$ins[3]] = $cpustate[ $ins[1] ] | $ins[2];                 break;
         case "setr":$cpustate[$ins[3]] = $cpustate[ $ins[1] ];                           break;
         case "seti":$cpustate[$ins[3]] = $ins[1];                                        break;
         case "gtir":$cpustate[$ins[3]] = ($ins[1]        >  $cpustate[$ins[2]]) ? 1 : 0; break;
         case "gtri":$cpustate[$ins[3]] = ($cpustate[$ins[1]]  >  $ins[2]      ) ? 1 : 0; break;
         case "gtrr":$cpustate[$ins[3]] = ($cpustate[$ins[1]]  >  $cpustate[$ins[2]]) ? 1 : 0; break;
         case "eqir":$cpustate[$ins[3]] = ($ins[1]       === $cpustate[$ins[2]]) ? 1 : 0; break;
         case "eqri":$cpustate[$ins[3]] = ($cpustate[$ins[1]] === $ins[2]      ) ? 1 : 0; break;
         case "eqrr":$cpustate[$ins[3]] = ($cpustate[$ins[1]] === $cpustate[$ins[2]]) ? 1 : 0; break;
        }
        if( $c > 30 ){
            // Heuristic speedup (determined by looking hard at goal and purpose of the input):
            $n = Amax($cpustate);
            //printf("After 30 steps, the probable factorized number (biggest register) is: %d\n",$n);
            $sqrN = (int) sqrt($n);
            $result = 0; for ($i = 1; $i <= $sqrN; $i++) if ($n % $i === 0) $result += $i + $n / $i;
            //printf("Result of the program should be: %d\n", $result);
            $cpustate[ 0 ] = $result ;
            break;
        }
        $cpustate[ $ipidx  ]++;
        $c++;
    }
    //printf("CPU at step: %-3d %s \n", $c, state2string($cpustate));
    return $cpustate;
}

printf("Part 1 answer (content of register 0, after program termination): %s\n", simulateProgram($program, $ipidx, [0,0,0, 0,0,0])[0]);
printf("Part 2 answer (content of register 0, after program termination): %s\n", simulateProgram($program, $ipidx, [1,0,0, 0,0,0])[0]);

function state2string($state){ $res = []; foreach( $state as $rname=>$rval) $res[]=sprintf("%8s",$rval);  return '['.join(',', $res).']'; }