protected function shortenZeroes($content)
{
// reusable bits of code throughout these regexes:
// before & after are used to make sure we don't match lose unintended
// 0-like values (e.g. in #000, or in http://url/1.0)
// units can be stripped from 0 values, or used to recognize non 0
// values (where wa may be able to strip a .0 suffix)
$before = '(?<=[:(, ])';
$after = '(?=[ ,);}])';
$units = '(em|ex|%|px|cm|mm|in|pt|pc|ch|rem|vh|vw|vmin|vmax|vm)';
// strip units after zeroes (0px -> 0)
// NOTE: it should be safe to remove all units for a 0 value, but in
// practice, Webkit (especially Safari) seems to stumble over at least
// 0%, potentially other units as well. Only stripping 'px' for now.
// @see https://github.com/matthiasmullie/minify/issues/60
$content = preg_replace('/' . $before . '(-?0*(\\.0+)?)(?<=0)px' . $after . '/', '\\1', $content);
// strip 0-digits (.0 -> 0)
$content = preg_replace('/' . $before . '\\.0+' . $units . '?' . $after . '/', '0\\1', $content);
// strip trailing 0: 50.10 -> 50.1, 50.10px -> 50.1px
$content = preg_replace('/' . $before . '(-?[0-9]+\\.[0-9]+)0+' . $units . '?' . $after . '/', '\\1\\2', $content);
// strip trailing 0: 50.00 -> 50, 50.00px -> 50px
$content = preg_replace('/' . $before . '(-?[0-9]+)\\.0+' . $units . '?' . $after . '/', '\\1\\2', $content);
// strip leading 0: 0.1 -> .1, 01.1 -> 1.1
$content = preg_replace('/' . $before . '(-?)0+([0-9]*\\.[0-9]+)' . $units . '?' . $after . '/', '\\1\\2\\3', $content);
// strip negative zeroes (-0 -> 0) & truncate zeroes (00 -> 0)
$content = preg_replace('/' . $before . '-?0+' . $units . '?' . $after . '/', '0\\1', $content);
// remove zeroes where they make no sense in calc: e.g. calc(100px - 0)
// the 0 doesn't have any effect, and this isn't even valid without unit
// strip all `+ 0` or `- 0` occurrences: calc(10% + 0) -> calc(10%)
// looped because there may be multiple 0s inside 1 group of parentheses
do {
$previous = $content;
$content = preg_replace('/\\(([^\\(\\)]+)\\s+[\\+\\-]\\s+0(\\s+[^\\(\\)]+)?\\)/', '(\\1\\2)', $content);
} while ($content !== $previous);
// strip all `0 +` occurrences: calc(0 + 10%) -> calc(10%)
$content = preg_replace('/\\(\\s*0\\s+\\+\\s+([^\\(\\)]+)\\)/', '(\\1)', $content);
// strip all `0 -` occurrences: calc(0 - 10%) -> calc(-10%)
$content = preg_replace('/\\(\\s*0\\s+\\-\\s+([^\\(\\)]+)\\)/', '(-\\1)', $content);
// I'm not going to attempt to optimize away `x * 0` instances:
// it's dumb enough code already that it likely won't occur, and it's
// too complex to do right (order of operations would have to be
// respected etc)
// what I cared about most here was fixing incorrectly truncated units
return $content;
}