private function determineSignatureBegin()
    {
        // detect signature position
        if (!preg_match('{__HALT_COMPILER\(\);(?: +\?>)?\r?\n}', $this->contents, $match, PREG_OFFSET_CAPTURE)) {
            throw new \RuntimeException('Could not detect the stub\'s end in the phar');
        }

        // set starting position and skip past manifest length
        $pos = $match[0][1] + strlen($match[0][0]);
        $stubEnd = $pos + $this->readUint($pos, 4);

        $pos += 4;
        $numFiles = $this->readUint($pos, 4);

        $pos += 4;

        // skip API version (YOLO)
        $pos += 2;

        // skip PHAR flags
        $pos += 4;

        $aliasLength = $this->readUint($pos, 4);
        $pos += 4 + $aliasLength;

        $metadataLength = $this->readUint($pos, 4);
        $pos += 4 + $metadataLength;

        $compressedSizes = 0;
        while ($pos < $stubEnd) {
            $filenameLength = $this->readUint($pos, 4);
            $pos += 4 + $filenameLength;

            // skip filesize and timestamp
            $pos += 2*4;

            $compressedSizes += $this->readUint($pos, 4);
            // skip compressed file size, crc32 checksum and file flags
            $pos += 3*4;

            $metadataLength = $this->readUint($pos, 4);
            $pos += 4 + $metadataLength;

            $numFiles--;
        }

        if ($numFiles !== 0) {
            throw new \LogicException('All files were not processed, something must have gone wrong');
        }

        return $pos + $compressedSizes;
    }