Method writeCount

zstd/fse_encoder.go:488–598

writeCount will write the normalized histogram count to header. This is read back by readNCount.

(out []byte)

// writeCount will write the normalized histogram count to header.
// This is read back by readNCount.
func (s *fseEncoder) writeCount(out []byte) ([]byte, error) {
	if s.useRLE {
		return append(out, s.rleVal), nil
	}
	if s.preDefined || s.reUsed {
		// Never write predefined.
		return out, nil
	}

	var (
		tableLog  = s.actualTableLog
		tableSize = 1 << tableLog
		previous0 bool
		charnum   uint16

		// maximum header size plus 2 extra bytes for final output if bitCount == 0.
		maxHeaderSize = ((int(s.symbolLen) * int(tableLog)) >> 3) + 3 + 2

		// Write Table Size
		bitStream = uint32(tableLog - minEncTablelog)
		bitCount  = uint(4)
		remaining = int16(tableSize + 1) /* +1 for extra accuracy */
		threshold = int16(tableSize)
		nbBits    = uint(tableLog + 1)
		outP      = len(out)
	)
	if cap(out) < outP+maxHeaderSize {
		out = append(out, make([]byte, maxHeaderSize*3)...)
		out = out[:len(out)-maxHeaderSize*3]
	}
	out = out[:outP+maxHeaderSize]

	// stops at 1
	for remaining > 1 {
		if previous0 {
			start := charnum
			for s.norm[charnum] == 0 {
				charnum++
			}
			for charnum >= start+24 {
				start += 24
				bitStream += uint32(0xFFFF) << bitCount
				out[outP] = byte(bitStream)
				out[outP+1] = byte(bitStream >> 8)
				outP += 2
				bitStream >>= 16
			}
			for charnum >= start+3 {
				start += 3
				bitStream += 3 << bitCount
				bitCount += 2
			}
			bitStream += uint32(charnum-start) << bitCount
			bitCount += 2
			if bitCount > 16 {
				out[outP] = byte(bitStream)
				out[outP+1] = byte(bitStream >> 8)
				outP += 2