A random key generater within PHP

generater.php

function rand_char($length) {
  $random = '';
  for ($i = 0; $i < $length; $i++) {
    $random .= chr(mt_rand(33, 126));
  }
  return $random;
}

function rand_sha1($length) {
  $max = ceil($length / 40);
  $random = '';
  for ($i = 0; $i < $max; $i ++) {
    $random .= sha1(microtime(true).mt_rand(10000,90000));
  }
  return substr($random, 0, $length);
}

function rand_md5($length) {
  $max = ceil($length / 32);
  $random = '';
  for ($i = 0; $i < $max; $i ++) {
    $random .= md5(microtime(true).mt_rand(10000,90000));
  }
  return substr($random, 0, $length);
}

$a = microtime(true);
for ($x = 0; $x < 1000; $x++)
  $temp = rand_char(1000);

echo "Rand:\t".(microtime(true) - $a)."\n";

$a = microtime(true);
for ($x = 0; $x < 1000; $x++)
  $temp = rand_sha1(1000);

echo "SHA-1:\t".(microtime(true) - $a)."\n";

$a = microtime(true);
for ($x = 0; $x < 1000; $x++)
  $temp = rand_md5(1000);

echo "MD5:\t".(microtime(true) - $a)."\n";