1 common.inc | `valid_number_step($value, $step, $offset = 0.0)` |

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...

### Related topics

### File

- core/
includes/ common.inc, line 1453 - Common functions that many Backdrop modules will need to reference.

### Code

```
function 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);
}
```