Convert between byte size units

ConvertByteSize.php

<?php

namespace LajosBencz;

class ConvertByteSize
{
    const FORMAT_BYTE_SIZE_PATTERN = '(yotta|zetta|exa|peta|tera|giga|mega|kilo|y|z|e|p|t|g|m|k)\s*(bit|byte|b)?';

    public static $formatByteSize_Unit = 'mB';
    public static $formatByteSize_Format = '%0.2f %s';

    public static function format($value, $unit=null, $format=null) {
        if(!$unit) {
            $unit = self::$formatByteSize_Unit;
        }
        if(!$format) {
            $format = self::$formatByteSize_Format;
        }

        static $exponents;
        if(!$exponents) {
            $exponents = array_flip(['','k','m','g','t','p','e','z','y']);
        }

        if(preg_match('/'.self::FORMAT_BYTE_SIZE_PATTERN.'/i',$unit,$match)) {
            $ru = strtolower($match[1][0]);
            $rb = $match[2]?:self::$formatByteSize_Unit[1];
        } else {
            $ru = self::$formatByteSize_Unit[0];
            $rb = self::$formatByteSize_Unit[1];
        }
        $mru = pow(1024,intval($exponents[$ru]));
        $mrb = ($rb == 'b' || $rb == 'bit') ? 8 : 1;
        unset($match);

        if(preg_match('/([\d\s\.\,]+)\s*(?:'.self::FORMAT_BYTE_SIZE_PATTERN.')?/i',$value,$match)) {
            $v = floatval(str_replace([' ',','],['','.'],$match[1]));
            $vu = $match[2]?strtolower($match[2][0]):'';
            $vb = $match[3]?:'B';
            $mvu = pow(1024,intval($exponents[$vu]));
            $mvb = ($vb == 'b' || $vb == 'bit') ? 8 : 1;

            $v*= $mvu;
            $v*= $mvb;
            $v/= $mru;
            $v*= $mrb;

            if(is_callable($format)) {
                return call_user_func_array($format,[$v,$unit]);
            }
            return sprintf($format,$v,$unit);
        }
        return $value;
    }
}