Trial Division Primality in PHP

<?php
declare(strict_types=1);
// Trial Division Primality in PHP
//
// PURPOSE
// A composite integer has a factor no larger than its square root. Trial division checks
// only candidate divisors up to that bound.
//
// METHOD
// Reject values below two, handle two, and reject other even values. Test odd divisors until
// d exceeds n/d, which avoids computing d squared.
//
// COMPLEXITY
// O(sqrt(n)) time and O(1) auxiliary space.
//
// CONTRACT
// Returns 1 for prime, 0 otherwise. This is suitable for small integers, not large
// cryptographic candidates.
// Public APIs infer array lengths except in C, which accepts pointer/length pairs. Vertex
// counts and matrix dimensions remain explicit. Arrays must contain signed 32-bit integers.
// Sorted order, correct tree topology, and caller-owned data-structure invariants are
// preconditions; checking them on every query would change query complexity.
// Scalar and shape checks are included. Value-range checks are included where needed to
// prevent invalid indexing or nontermination. Allocation sizes are capped at 4,000,000
// workspace entries. Arithmetic outside Python raises an error on 32-bit overflow; Python
// uses arbitrary precision. Native allocation failures propagate. In-place outputs may be
// partly updated after arithmetic failure. These are single-threaded, in-memory
// implementations.
//
// LANGUAGE DETAILS
// PHP 8.1+ on a 64-bit runtime: packed arrays, strict scalar types, read-only inputs by
// value using copy-on-write, references only for outputs, and checked 32-bit arithmetic.
// Invalid input and overflow throw exceptions. PHP arrays have higher overhead than native
// packed buffers in C/Java.
//
// EXAMPLE
// Expected return: 1.
// Run: php example.php
// Tests for this exact source artifact run before publication. The accompanying source
// archive includes unit cases, runtime results, and source hashes.

function alg_require(bool $valid): void { if (!$valid) throw new InvalidArgumentException("invalid algorithm input"); }
function alg_checked(int|float $v): int { if ($v < -2147483648 || $v > 2147483647 || floor($v) != $v) throw new OverflowException("32-bit result overflow"); return (int)$v; }
function alg_add(int $a,int $b): int { return alg_checked($a+$b); }
function alg_sub(int $a,int $b): int { return alg_checked($a-$b); }
function alg_mul(int $a,int $b): int { return alg_checked($a*$b); }
function alg_size(int $n): int { alg_require($n>=0 && $n<=4000000); return $n; }

function is_prime(int $n): int {
    if (($n < 2)) {
        return 0;
    }
    if (($n == 2)) {
        return 1;
    }
    if ((($n % 2) == 0)) {
        return 0;
    }
    $d = 3;
    while (($d <= intdiv($n, $d))) {
        if ((($n % $d) == 0)) {
            return 0;
        }
        $d = alg_add($d, 2);
    }
    return 1;
}

$n = 97;
$result = is_prime($n);
echo $result, PHP_EOL;