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

float $value: The value that needs to be checked.

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

float $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 occurred, or FALSE otherwise.

See also

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

3 calls to Number::validStep()

Number::validateNumber in core/lib/Drupal/Core/Render/Element/Number.php

Form element validation handler for #type 'number'.

NumberTest::testValidStep in core/tests/Drupal/Tests/Component/Utility/NumberTest.php

Tests Number::validStep() without offset.

NumberTest::testValidStepOffset in core/tests/Drupal/Tests/Component/Utility/NumberTest.php

Tests Number::validStep() with offset.

File

core/lib/Drupal/Component/Utility/Number.php, line 33

Class

Number

Provides helper methods for manipulating numbers.

Namespace

Drupal\Component\Utility

Code

public static function validStep($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;
}

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