Advent of code 2017/15
Ajax Direct

Answer ⏱

Part 1 : Part 2 : 
const FACTOR_A    = 16807;
const FACTOR_B    = 48271;
const DIVISOR     = 2147483647;
CONST BITMASK_16  = 0xFFFF;

// ==================================================
// > PART 1
// ==================================================
[$a, $b] = $input->numbers;
$solution_1 = 0;

for ($i = 0; $i <= 40_000_000; $i++) {
    $a = ($a * FACTOR_A) % DIVISOR;
    $b = ($b * FACTOR_B) % DIVISOR;
    if (($a & BITMASK_16) === ($b & BITMASK_16)) $solution_1++;
}

// ==================================================
// > PART 2
// ==================================================
[$a, $b] = $input->numbers;
$solution_2 = 0;

for ($i = 0; $i <= 5_000_000; $i++) {
    do {
        $a = ($a * FACTOR_A) % DIVISOR;
    } while ($a % 4 !== 0);

    do {
        $b = ($b * FACTOR_B) % DIVISOR;
    } while ($b % 8 !== 0);

    if (($a & BITMASK_16) === ($b & BITMASK_16)) $solution_2++;
}