Array Rotation by Reversal in PHP

<?php
declare(strict_types=1);
// Array Rotation by Reversal in PHP
//
// PURPOSE
// Three reversals rotate an array right without a second array.
//
// METHOD
// Normalize k modulo length. Reverse the whole array, then reverse the first k elements and
// the remaining suffix.
//
// COMPLEXITY
// O(n) time, O(1) auxiliary space.
//
// CONTRACT
// k >= 0. Rotates right in place, returns 0. Empty input is valid.
// 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: 0.
// Expected a after call: [4, 1, 2, 3].
// 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 rotate_right(array &$a, int $k): int {
    alg_require(array_is_list($a));
    $n = count($a);
    alg_require((($n >= 0) && ($n <= 1000000)));
    alg_require((count($a) == $n));
    alg_require(($k >= 0));
    if (($n == 0)) {
        return 0;
    }
    $k = ($k % $n);
    $phase = 0;
    $left = 0;
    $right = 0;
    $temp = 0;
    while (($phase < 3)) {
        if (($phase == 0)) {
            $left = 0;
            $right = alg_sub($n, 1);
        } else {
            if (($phase == 1)) {
                $left = 0;
                $right = alg_sub($k, 1);
            } else {
                $left = $k;
                $right = alg_sub($n, 1);
            }
        }
        while (($left < $right)) {
            $temp = $a[$left];
            $a[$left] = $a[$right];
            $a[$right] = $temp;
            $left = alg_add($left, 1);
            $right = alg_sub($right, 1);
        }
        $phase = alg_add($phase, 1);
    }
    return 0;
}

$a = [1, 2, 3, 4];
$k = 1;
$result = rotate_right($a, $k);
echo $result, PHP_EOL;
// Expected a: [4, 1, 2, 3]
echo json_encode($a), PHP_EOL;