Method writeTo

roaringarray.go:493–567

spec: https://github.com/RoaringBitmap/RoaringFormatSpec

(w io.Writer)

// spec: https://github.com/RoaringBitmap/RoaringFormatSpec
func (ra *roaringArray) writeTo(w io.Writer) (n int64, err error) {
	hasRun := ra.hasRunCompression()
	isRunSizeInBytes := 0
	cookieSize := 8
	if hasRun {
		cookieSize = 4
		isRunSizeInBytes = (len(ra.keys) + 7) / 8
	}
	descriptiveHeaderSize := 4 * len(ra.keys)
	preambleSize := cookieSize + isRunSizeInBytes + descriptiveHeaderSize

	buf := make([]byte, preambleSize+4*len(ra.keys))

	nw := 0

	if hasRun {
		binary.LittleEndian.PutUint16(buf[0:], uint16(serialCookie))
		nw += 2
		binary.LittleEndian.PutUint16(buf[2:], uint16(len(ra.keys)-1))
		nw += 2
		// compute isRun bitmap without temporary allocation
		runbitmapslice := buf[nw : nw+isRunSizeInBytes]
		for i, c := range ra.containers {
			switch c.(type) {
			case *runContainer16:
				runbitmapslice[i/8] |= 1 << (uint(i) % 8)
			}
		}
		nw += isRunSizeInBytes
	} else {
		binary.LittleEndian.PutUint32(buf[0:], uint32(serialCookieNoRunContainer))
		nw += 4
		binary.LittleEndian.PutUint32(buf[4:], uint32(len(ra.keys)))
		nw += 4
	}

	// descriptive header
	for i, key := range ra.keys {
		binary.LittleEndian.PutUint16(buf[nw:], key)
		nw += 2
		c := ra.containers[i]
		binary.LittleEndian.PutUint16(buf[nw:], uint16(c.getCardinality()-1))
		nw += 2
	}

	startOffset := int64(preambleSize + 4*len(ra.keys))
	if !hasRun || (len(ra.keys) >= noOffsetThreshold) {
		// offset header
		for _, c := range ra.containers {
			binary.LittleEndian.PutUint32(buf[nw:], uint32(startOffset))
			nw += 4
			switch rc := c.(type) {
			case *runContainer16:
				startOffset += 2 + int64(len(rc.iv))*4
			default:
				startOffset += int64(getSizeInBytesFromCardinality(c.getCardinality()))
			}
		}