exercism-php/all-your-base/AllYourBase.php

<?php

/*
 * By adding type hints and enabling strict type checking, code can become
 * easier to read, self-documenting and reduce the number of potential bugs.
 * By default, type declarations are non-strict, which means they will attempt
 * to change the original type to match the type specified by the
 * type-declaration.
 *
 * In other words, if you pass a string to a function requiring a float,
 * it will attempt to convert the string value to a float.
 *
 * To enable strict mode, a single declare directive must be placed at the top
 * of the file.
 * This means that the strictness of typing is configured on a per-file basis.
 * This directive not only affects the type declarations of parameters, but also
 * a function's return type.
 *
 * For more info review the Concept on strict type checking in the PHP track
 * <link>.
 *
 * To disable strict typing, comment out the directive below.
 */

declare(strict_types=1);

const ErrInBase = "input base must be >= 2";
const ErrOutBase = "output base must be >= 2";
const ErrDigits = "all digits must satisfy 0 <= d < input base";

function rebase(int $fromBase, array $digits, int $toBase): array {
  if ($fromBase < 2) {
    throw new \InvalidArgumentException(ErrInBase);
  }
  if ($toBase < 2) {
    throw new \InvalidArgumentException(ErrOutBase);
  }
  if ($fromBase === $toBase) {
    return $digits;
  }
  $rev = array_reverse($digits);

  $value = 0;
  $pow = 1;
  foreach ($rev as $digit) {
    if ($digit < 0 || $digit >= $fromBase) {
      throw new \InvalidArgumentException(ErrDigits);
    }
    $value += $digit * $pow;
    $pow *= $fromBase;
  }

  $reversed = [];
  $current = $value;
  while (TRUE) {
    $reversed[] = $current % $toBase;
    $current = (int) ($current / $toBase);
    if ($current === 0) {
      break;
    }
  }
  $out = array_reverse($reversed);
  return $out;
}