base64文字列を配列形式にする

array_from_base64_decode.php

<?php
/**
 * @param string $str
 * @return array
 */
function array_from_base64_decode( $str ) {
  $table = preg_split('//', 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/', -1, PREG_SPLIT_NO_EMPTY);
  $data = array();
  for( $i=0, $l=count($table); $i<$l; $i++) {
    $data[$table[$i]] = $i;
  }
  $a = array();
  $b = preg_split('//', $str, -1, PREG_SPLIT_NO_EMPTY);
  $l = count( $b );
  $b[$l - 1] === '=' && $l--;
  $b[$l - 1] === '=' && $l--;
  $b[$l - 1] === '=' && $l--;
  $m = count($b) - $l;
  for( $i=0, $j=0; $i<=$l-4; $i+=4 ) {
    $k = ( $data[$b[$i]] << 18) | ($data[$b[$i+1]] << 12) | ($data[$b[$i+2]] << 6) | $data[$b[$i+3]];
    $a[$j++] = $k >> 16 & 255;
    $a[$j++] = $k >> 8 & 255;
    $a[$j++] = $k & 255;
  }
  if($m == 1) {
    $k = ($data[$b[$i]] << 18) | ($data[$b[$i+1]] << 12) | ($data[$b[$i+2]] << 6);
    $a[$j++] = $k >> 16 & 255;
    $a[$j] = $k >> 8 & 255;
  } else if($m == 2) {
    $k = ($data[$b[$i]] << 18) | ($data[$b[$i + 1]] << 12);
    $a[$j] = $k >> 16 & 255;
  }
  return $a;
}

var_dump( array_from_base64_decode( "AQIDBA==" ) );
/*
array(4) {
  [0]=>
  int(1)
  [1]=>
  int(2)
  [2]=>
  int(3)
  [3]=>
  int(4)
}
*/