function elements_valid_number_step in Elements 7

Verifies that a number is a multiple of a given step.

The implementation assumes it is dealing with IEEE 754 double precision floating point numbers that are used by PHP on most systems.

This is based on the number/range verification methods of webkit.

Parameters

$value: The value that needs to be checked.

$step: The step scale factor. Must be positive.

$offset: (optional) An offset, to which the difference must be a multiple of the given step.

Return value

bool TRUE if no step mismatch has occured, or FALSE otherwise.

See also

http://opensource.apple.com/source/WebCore/WebCore-1298/html/NumberInput...

1 call to elements_valid_number_step()

elements_validate_number in ./elements.module

Form element validation handler for #type 'number'.

File

./elements.module, line 324

Code

function elements_valid_number_step($value, $step, $offset = 0.0) {
  $double_value = (double) abs($value - $offset);

  // The fractional part of a double has 53 bits. The greatest number that could
  // be represented with that is 2^53. If the given value is even bigger than
  // $step * 2^53, then dividing by $step will result in a very small remainder.
  // Since that remainder can't even be represented with a single precision
  // float the following computation of the remainder makes no sense and we can
  // safely ignore it instead.
  if ($double_value / pow(2.0, 53) > $step) {
    return TRUE;
  }

  // Now compute that remainder of a division by $step.
  $remainder = (double) abs($double_value - $step * round($double_value / $step));

  // $remainder is a double precision floating point number. Remainders that
  // can't be represented with single precision floats are acceptable. The
  // fractional part of a float has 24 bits. That means remainders smaller than
  // $step * 2^-24 are acceptable.
  $computed_acceptable_error = (double) ($step / pow(2.0, 24));
  return $computed_acceptable_error >= $remainder || $remainder >= $step - $computed_acceptable_error;
}