Validate the html5 step attribute in PHP

gistfile1.php

<?php
/**
 * php port from C++
 * All the logic taken from the chrome/webkit/idk team ;)
 * http://codesearch.google.com/#OAMlx_jo-ck/src/third_party/WebKit/Source/WebCore/html/NumberInputType.cpp&type=cs&l=129&q=acceptableError&exact_package=chromium
 */

define ("DBL_MANT_DIG", 16);
define ("FLT_MANT_DIG", 16);

/**
 * returns TRUE is there is a mis match
 */
function stepMismatch($value, $step) {
    (double) $doubleValue;
    
    if (!$doubleValue = (double) $value) {
      return false;      
    }
    $doubleValue = abs($doubleValue - 0.0);
    if (is_infinite($doubleValue)) {
      return false;      
    }
    // double's fractional part size is DBL_MAN_DIG-bit. If the current value
    // is greater than step*2^DBL_MANT_DIG, the following computation for
    // remainder makes no sense.
    if ($doubleValue / pow(2.0, DBL_MANT_DIG) > $step) {
      return false;      
    }
    // The computation follows HTML5 4.10.7.2.10 `The step attribute' :
    // ... that number subtracted from the step base is not an integral multiple
    // of the allowed value step, the element is suffering from a step mismatch.
    (double) $remainder = abs($doubleValue - $step * round($doubleValue / $step));
    // Accepts erros in lower fractional part which IEEE 754 single-precision
    // can't represent.
    (double) $computedAcceptableError = acceptableError($step);
    return $computedAcceptableError < $remainder && $remainder < ($step - $computedAcceptableError);
}

function acceptableError($step) {
    return $step / pow(2.0, FLT_MANT_DIG);
}


$value = 1.2;
$step = 0.4;

if (stepMismatch($value, $step)) {
  print "INVALID";
}
else {
  print "VALID"; // VALID is Printed
}

$value = 1.2;
$step = 0.5;

if (stepMismatch($value, $step)) {
  print "INVALID"; // INVALID Is Printer
}
else {
  print "VALID";
}

there some useless stuff in here, but is way to late for me to fix that now.