Use goreleaser to build and release (#244)

Instead of using gox on one side and an action to release, we can merge
them together with goreleaser which will build for extra targets (arm,
mips if needed in the future) and it also takes care of creating
checksums, a source archive, and a changelog and creating a release with
all the artifacts.

All binaries should respect the old naming convention, so any scripts
out there should still work.

Signed-off-by: Itxaka <igarcia@suse.com>

vendor/github.com/klauspost/compress/flate/huffman_bit_writer.go

@@ -5,6 +5,7 @@
 package flate
 
 import (
+	"encoding/binary"
 	"io"
 )
 
@@ -85,26 +86,48 @@ type huffmanBitWriter struct {
 	// Data waiting to be written is bytes[0:nbytes]
 	// and then the low nbits of bits.
 	bits            uint64
-	nbits           uint
-	bytes           [256]byte
-	codegenFreq     [codegenCodeCount]int32
+	nbits           uint16
 	nbytes          uint8
-	literalFreq     []int32
-	offsetFreq      []int32
-	codegen         []uint8
 	literalEncoding *huffmanEncoder
 	offsetEncoding  *huffmanEncoder
 	codegenEncoding *huffmanEncoder
 	err             error
+	lastHeader      int
+	// Set between 0 (reused block can be up to 2x the size)
+	logNewTablePenalty uint
+	lastHuffMan        bool
+	bytes              [256]byte
+	literalFreq        [lengthCodesStart + 32]uint16
+	offsetFreq         [32]uint16
+	codegenFreq        [codegenCodeCount]uint16
+
+	// codegen must have an extra space for the final symbol.
+	codegen [literalCount + offsetCodeCount + 1]uint8
 }
 
+// Huffman reuse.
+//
+// The huffmanBitWriter supports reusing huffman tables and thereby combining block sections.
+//
+// This is controlled by several variables:
+//
+// If lastHeader is non-zero the Huffman table can be reused.
+// This also indicates that a Huffman table has been generated that can output all
+// possible symbols.
+// It also indicates that an EOB has not yet been emitted, so if a new tabel is generated
+// an EOB with the previous table must be written.
+//
+// If lastHuffMan is set, a table for outputting literals has been generated and offsets are invalid.
+//
+// An incoming block estimates the output size of a new table using a 'fresh' by calculating the
+// optimal size and adding a penalty in 'logNewTablePenalty'.
+// A Huffman table is not optimal, which is why we add a penalty, and generating a new table
+// is slower both for compression and decompression.
+
 func newHuffmanBitWriter(w io.Writer) *huffmanBitWriter {
 	return &huffmanBitWriter{
 		writer:          w,
-		literalFreq:     make([]int32, lengthCodesStart+32),
-		offsetFreq:      make([]int32, 32),
-		codegen:         make([]uint8, maxNumLit+offsetCodeCount+1),
-		literalEncoding: newHuffmanEncoder(maxNumLit),
+		literalEncoding: newHuffmanEncoder(literalCount),
 		codegenEncoding: newHuffmanEncoder(codegenCodeCount),
 		offsetEncoding:  newHuffmanEncoder(offsetCodeCount),
 	}
@@ -113,7 +136,41 @@ func newHuffmanBitWriter(w io.Writer) *huffmanBitWriter {
 func (w *huffmanBitWriter) reset(writer io.Writer) {
 	w.writer = writer
 	w.bits, w.nbits, w.nbytes, w.err = 0, 0, 0, nil
-	w.bytes = [256]byte{}
+	w.lastHeader = 0
+	w.lastHuffMan = false
+}
+
+func (w *huffmanBitWriter) canReuse(t *tokens) (offsets, lits bool) {
+	offsets, lits = true, true
+	a := t.offHist[:offsetCodeCount]
+	b := w.offsetFreq[:len(a)]
+	for i := range a {
+		if b[i] == 0 && a[i] != 0 {
+			offsets = false
+			break
+		}
+	}
+
+	a = t.extraHist[:literalCount-256]
+	b = w.literalFreq[256:literalCount]
+	b = b[:len(a)]
+	for i := range a {
+		if b[i] == 0 && a[i] != 0 {
+			lits = false
+			break
+		}
+	}
+	if lits {
+		a = t.litHist[:]
+		b = w.literalFreq[:len(a)]
+		for i := range a {
+			if b[i] == 0 && a[i] != 0 {
+				lits = false
+				break
+			}
+		}
+	}
+	return
 }
 
 func (w *huffmanBitWriter) flush() {
@@ -121,6 +178,11 @@ func (w *huffmanBitWriter) flush() {
 		w.nbits = 0
 		return
 	}
+	if w.lastHeader > 0 {
+		// We owe an EOB
+		w.writeCode(w.literalEncoding.codes[endBlockMarker])
+		w.lastHeader = 0
+	}
 	n := w.nbytes
 	for w.nbits != 0 {
 		w.bytes[n] = byte(w.bits)
@@ -144,30 +206,11 @@ func (w *huffmanBitWriter) write(b []byte) {
 	_, w.err = w.writer.Write(b)
 }
 
-func (w *huffmanBitWriter) writeBits(b int32, nb uint) {
+func (w *huffmanBitWriter) writeBits(b int32, nb uint16) {
 	w.bits |= uint64(b) << w.nbits
 	w.nbits += nb
 	if w.nbits >= 48 {
-		bits := w.bits
-		w.bits >>= 48
-		w.nbits -= 48
-		n := w.nbytes
-		w.bytes[n] = byte(bits)
-		w.bytes[n+1] = byte(bits >> 8)
-		w.bytes[n+2] = byte(bits >> 16)
-		w.bytes[n+3] = byte(bits >> 24)
-		w.bytes[n+4] = byte(bits >> 32)
-		w.bytes[n+5] = byte(bits >> 40)
-		n += 6
-		if n >= bufferFlushSize {
-			if w.err != nil {
-				n = 0
-				return
-			}
-			w.write(w.bytes[:n])
-			n = 0
-		}
-		w.nbytes = n
+		w.writeOutBits()
 	}
 }
 
@@ -213,7 +256,7 @@ func (w *huffmanBitWriter) generateCodegen(numLiterals int, numOffsets int, litE
 	// a copy of the frequencies, and as the place where we put the result.
 	// This is fine because the output is always shorter than the input used
 	// so far.
-	codegen := w.codegen // cache
+	codegen := w.codegen[:] // cache
 	// Copy the concatenated code sizes to codegen. Put a marker at the end.
 	cgnl := codegen[:numLiterals]
 	for i := range cgnl {
@@ -292,30 +335,61 @@ func (w *huffmanBitWriter) generateCodegen(numLiterals int, numOffsets int, litE
 	codegen[outIndex] = badCode
 }
 
-// dynamicSize returns the size of dynamically encoded data in bits.
-func (w *huffmanBitWriter) dynamicSize(litEnc, offEnc *huffmanEncoder, extraBits int) (size, numCodegens int) {
+func (w *huffmanBitWriter) codegens() int {
+	numCodegens := len(w.codegenFreq)
+	for numCodegens > 4 && w.codegenFreq[codegenOrder[numCodegens-1]] == 0 {
+		numCodegens--
+	}
+	return numCodegens
+}
+
+func (w *huffmanBitWriter) headerSize() (size, numCodegens int) {
 	numCodegens = len(w.codegenFreq)
 	for numCodegens > 4 && w.codegenFreq[codegenOrder[numCodegens-1]] == 0 {
 		numCodegens--
 	}
-	header := 3 + 5 + 5 + 4 + (3 * numCodegens) +
+	return 3 + 5 + 5 + 4 + (3 * numCodegens) +
 		w.codegenEncoding.bitLength(w.codegenFreq[:]) +
 		int(w.codegenFreq[16])*2 +
 		int(w.codegenFreq[17])*3 +
-		int(w.codegenFreq[18])*7
-	size = header +
-		litEnc.bitLength(w.literalFreq) +
-		offEnc.bitLength(w.offsetFreq) +
-		extraBits
+		int(w.codegenFreq[18])*7, numCodegens
+}
 
+// dynamicSize returns the size of dynamically encoded data in bits.
+func (w *huffmanBitWriter) dynamicReuseSize(litEnc, offEnc *huffmanEncoder) (size int) {
+	size = litEnc.bitLength(w.literalFreq[:]) +
+		offEnc.bitLength(w.offsetFreq[:])
+	return size
+}
+
+// dynamicSize returns the size of dynamically encoded data in bits.
+func (w *huffmanBitWriter) dynamicSize(litEnc, offEnc *huffmanEncoder, extraBits int) (size, numCodegens int) {
+	header, numCodegens := w.headerSize()
+	size = header +
+		litEnc.bitLength(w.literalFreq[:]) +
+		offEnc.bitLength(w.offsetFreq[:]) +
+		extraBits
 	return size, numCodegens
 }
 
+// extraBitSize will return the number of bits that will be written
+// as "extra" bits on matches.
+func (w *huffmanBitWriter) extraBitSize() int {
+	total := 0
+	for i, n := range w.literalFreq[257:literalCount] {
+		total += int(n) * int(lengthExtraBits[i&31])
+	}
+	for i, n := range w.offsetFreq[:offsetCodeCount] {
+		total += int(n) * int(offsetExtraBits[i&31])
+	}
+	return total
+}
+
 // fixedSize returns the size of dynamically encoded data in bits.
 func (w *huffmanBitWriter) fixedSize(extraBits int) int {
 	return 3 +
-		fixedLiteralEncoding.bitLength(w.literalFreq) +
-		fixedOffsetEncoding.bitLength(w.offsetFreq) +
+		fixedLiteralEncoding.bitLength(w.literalFreq[:]) +
+		fixedOffsetEncoding.bitLength(w.offsetFreq[:]) +
 		extraBits
 }
 
@@ -333,32 +407,37 @@ func (w *huffmanBitWriter) storedSize(in []byte) (int, bool) {
 }
 
 func (w *huffmanBitWriter) writeCode(c hcode) {
+	// The function does not get inlined if we "& 63" the shift.
 	w.bits |= uint64(c.code) << w.nbits
-	w.nbits += uint(c.len)
+	w.nbits += c.len
 	if w.nbits >= 48 {
-		bits := w.bits
-		w.bits >>= 48
-		w.nbits -= 48
-		n := w.nbytes
-		w.bytes[n] = byte(bits)
-		w.bytes[n+1] = byte(bits >> 8)
-		w.bytes[n+2] = byte(bits >> 16)
-		w.bytes[n+3] = byte(bits >> 24)
-		w.bytes[n+4] = byte(bits >> 32)
-		w.bytes[n+5] = byte(bits >> 40)
-		n += 6
-		if n >= bufferFlushSize {
-			if w.err != nil {
-				n = 0
-				return
-			}
-			w.write(w.bytes[:n])
-			n = 0
-		}
-		w.nbytes = n
+		w.writeOutBits()
 	}
 }
 
+// writeOutBits will write bits to the buffer.
+func (w *huffmanBitWriter) writeOutBits() {
+	bits := w.bits
+	w.bits >>= 48
+	w.nbits -= 48
+	n := w.nbytes
+
+	// We over-write, but faster...
+	binary.LittleEndian.PutUint64(w.bytes[n:], bits)
+	n += 6
+
+	if n >= bufferFlushSize {
+		if w.err != nil {
+			n = 0
+			return
+		}
+		w.write(w.bytes[:n])
+		n = 0
+	}
+
+	w.nbytes = n
+}
+
 // Write the header of a dynamic Huffman block to the output stream.
 //
 //  numLiterals  The number of literals specified in codegen
@@ -384,34 +463,49 @@ func (w *huffmanBitWriter) writeDynamicHeader(numLiterals int, numOffsets int, n
 
 	i := 0
 	for {
-		var codeWord int = int(w.codegen[i])
+		var codeWord = uint32(w.codegen[i])
 		i++
 		if codeWord == badCode {
 			break
 		}
-		w.writeCode(w.codegenEncoding.codes[uint32(codeWord)])
+		w.writeCode(w.codegenEncoding.codes[codeWord])
 
 		switch codeWord {
 		case 16:
 			w.writeBits(int32(w.codegen[i]), 2)
 			i++
-			break
 		case 17:
 			w.writeBits(int32(w.codegen[i]), 3)
 			i++
-			break
 		case 18:
 			w.writeBits(int32(w.codegen[i]), 7)
 			i++
-			break
 		}
 	}
 }
 
+// writeStoredHeader will write a stored header.
+// If the stored block is only used for EOF,
+// it is replaced with a fixed huffman block.
 func (w *huffmanBitWriter) writeStoredHeader(length int, isEof bool) {
 	if w.err != nil {
 		return
 	}
+	if w.lastHeader > 0 {
+		// We owe an EOB
+		w.writeCode(w.literalEncoding.codes[endBlockMarker])
+		w.lastHeader = 0
+	}
+
+	// To write EOF, use a fixed encoding block. 10 bits instead of 5 bytes.
+	if length == 0 && isEof {
+		w.writeFixedHeader(isEof)
+		// EOB: 7 bits, value: 0
+		w.writeBits(0, 7)
+		w.flush()
+		return
+	}
+
 	var flag int32
 	if isEof {
 		flag = 1
@@ -426,6 +520,12 @@ func (w *huffmanBitWriter) writeFixedHeader(isEof bool) {
 	if w.err != nil {
 		return
 	}
+	if w.lastHeader > 0 {
+		// We owe an EOB
+		w.writeCode(w.literalEncoding.codes[endBlockMarker])
+		w.lastHeader = 0
+	}
+
 	// Indicate that we are a fixed Huffman block
 	var value int32 = 2
 	if isEof {
@@ -439,29 +539,23 @@ func (w *huffmanBitWriter) writeFixedHeader(isEof bool) {
 // is larger than the original bytes, the data will be written as a
 // stored block.
 // If the input is nil, the tokens will always be Huffman encoded.
-func (w *huffmanBitWriter) writeBlock(tokens []token, eof bool, input []byte) {
+func (w *huffmanBitWriter) writeBlock(tokens *tokens, eof bool, input []byte) {
 	if w.err != nil {
 		return
 	}
 
-	tokens = append(tokens, endBlockMarker)
-	numLiterals, numOffsets := w.indexTokens(tokens)
-
+	tokens.AddEOB()
+	if w.lastHeader > 0 {
+		// We owe an EOB
+		w.writeCode(w.literalEncoding.codes[endBlockMarker])
+		w.lastHeader = 0
+	}
+	numLiterals, numOffsets := w.indexTokens(tokens, false)
+	w.generate(tokens)
 	var extraBits int
 	storedSize, storable := w.storedSize(input)
 	if storable {
-		// We only bother calculating the costs of the extra bits required by
-		// the length of offset fields (which will be the same for both fixed
-		// and dynamic encoding), if we need to compare those two encodings
-		// against stored encoding.
-		for lengthCode := lengthCodesStart + 8; lengthCode < numLiterals; lengthCode++ {
-			// First eight length codes have extra size = 0.
-			extraBits += int(w.literalFreq[lengthCode]) * int(lengthExtraBits[lengthCode-lengthCodesStart])
-		}
-		for offsetCode := 4; offsetCode < numOffsets; offsetCode++ {
-			// First four offset codes have extra size = 0.
-			extraBits += int(w.offsetFreq[offsetCode]) * int(offsetExtraBits[offsetCode&63])
-		}
+		extraBits = w.extraBitSize()
 	}
 
 	// Figure out smallest code.
@@ -500,7 +594,7 @@ func (w *huffmanBitWriter) writeBlock(tokens []token, eof bool, input []byte) {
 	}
 
 	// Write the tokens.
-	w.writeTokens(tokens, literalEncoding.codes, offsetEncoding.codes)
+	w.writeTokens(tokens.Slice(), literalEncoding.codes, offsetEncoding.codes)
 }
 
 // writeBlockDynamic encodes a block using a dynamic Huffman table.
@@ -508,72 +602,103 @@ func (w *huffmanBitWriter) writeBlock(tokens []token, eof bool, input []byte) {
 // histogram distribution.
 // If input is supplied and the compression savings are below 1/16th of the
 // input size the block is stored.
-func (w *huffmanBitWriter) writeBlockDynamic(tokens []token, eof bool, input []byte) {
+func (w *huffmanBitWriter) writeBlockDynamic(tokens *tokens, eof bool, input []byte, sync bool) {
 	if w.err != nil {
 		return
 	}
 
-	tokens = append(tokens, endBlockMarker)
-	numLiterals, numOffsets := w.indexTokens(tokens)
-
-	// Generate codegen and codegenFrequencies, which indicates how to encode
-	// the literalEncoding and the offsetEncoding.
-	w.generateCodegen(numLiterals, numOffsets, w.literalEncoding, w.offsetEncoding)
-	w.codegenEncoding.generate(w.codegenFreq[:], 7)
-	size, numCodegens := w.dynamicSize(w.literalEncoding, w.offsetEncoding, 0)
-
-	// Store bytes, if we don't get a reasonable improvement.
-	if ssize, storable := w.storedSize(input); storable && ssize < (size+size>>4) {
-		w.writeStoredHeader(len(input), eof)
-		w.writeBytes(input)
-		return
+	sync = sync || eof
+	if sync {
+		tokens.AddEOB()
 	}
 
-	// Write Huffman table.
-	w.writeDynamicHeader(numLiterals, numOffsets, numCodegens, eof)
+	// We cannot reuse pure huffman table, and must mark as EOF.
+	if (w.lastHuffMan || eof) && w.lastHeader > 0 {
+		// We will not try to reuse.
+		w.writeCode(w.literalEncoding.codes[endBlockMarker])
+		w.lastHeader = 0
+		w.lastHuffMan = false
+	}
+	if !sync {
+		tokens.Fill()
+	}
+	numLiterals, numOffsets := w.indexTokens(tokens, !sync)
 
+	var size int
+	// Check if we should reuse.
+	if w.lastHeader > 0 {
+		// Estimate size for using a new table.
+		// Use the previous header size as the best estimate.
+		newSize := w.lastHeader + tokens.EstimatedBits()
+		newSize += newSize >> w.logNewTablePenalty
+
+		// The estimated size is calculated as an optimal table.
+		// We add a penalty to make it more realistic and re-use a bit more.
+		reuseSize := w.dynamicReuseSize(w.literalEncoding, w.offsetEncoding) + w.extraBitSize()
+
+		// Check if a new table is better.
+		if newSize < reuseSize {
+			// Write the EOB we owe.
+			w.writeCode(w.literalEncoding.codes[endBlockMarker])
+			size = newSize
+			w.lastHeader = 0
+		} else {
+			size = reuseSize
+		}
+		// Check if we get a reasonable size decrease.
+		if ssize, storable := w.storedSize(input); storable && ssize < (size+size>>4) {
+			w.writeStoredHeader(len(input), eof)
+			w.writeBytes(input)
+			w.lastHeader = 0
+			return
+		}
+	}
+
+	// We want a new block/table
+	if w.lastHeader == 0 {
+		w.generate(tokens)
+		// Generate codegen and codegenFrequencies, which indicates how to encode
+		// the literalEncoding and the offsetEncoding.
+		w.generateCodegen(numLiterals, numOffsets, w.literalEncoding, w.offsetEncoding)
+		w.codegenEncoding.generate(w.codegenFreq[:], 7)
+		var numCodegens int
+		size, numCodegens = w.dynamicSize(w.literalEncoding, w.offsetEncoding, w.extraBitSize())
+		// Store bytes, if we don't get a reasonable improvement.
+		if ssize, storable := w.storedSize(input); storable && ssize < (size+size>>4) {
+			w.writeStoredHeader(len(input), eof)
+			w.writeBytes(input)
+			w.lastHeader = 0
+			return
+		}
+
+		// Write Huffman table.
+		w.writeDynamicHeader(numLiterals, numOffsets, numCodegens, eof)
+		w.lastHeader, _ = w.headerSize()
+		w.lastHuffMan = false
+	}
+
+	if sync {
+		w.lastHeader = 0
+	}
 	// Write the tokens.
-	w.writeTokens(tokens, w.literalEncoding.codes, w.offsetEncoding.codes)
+	w.writeTokens(tokens.Slice(), w.literalEncoding.codes, w.offsetEncoding.codes)
 }
 
 // indexTokens indexes a slice of tokens, and updates
 // literalFreq and offsetFreq, and generates literalEncoding
 // and offsetEncoding.
 // The number of literal and offset tokens is returned.
-func (w *huffmanBitWriter) indexTokens(tokens []token) (numLiterals, numOffsets int) {
-	for i := range w.literalFreq {
-		w.literalFreq[i] = 0
-	}
-	for i := range w.offsetFreq {
-		w.offsetFreq[i] = 0
-	}
+func (w *huffmanBitWriter) indexTokens(t *tokens, filled bool) (numLiterals, numOffsets int) {
+	copy(w.literalFreq[:], t.litHist[:])
+	copy(w.literalFreq[256:], t.extraHist[:])
+	copy(w.offsetFreq[:], t.offHist[:offsetCodeCount])
 
-	if len(tokens) == 0 {
+	if t.n == 0 {
 		return
 	}
-
-	// Only last token should be endBlockMarker.
-	if tokens[len(tokens)-1] == endBlockMarker {
-		w.literalFreq[endBlockMarker]++
-		tokens = tokens[:len(tokens)-1]
+	if filled {
+		return maxNumLit, maxNumDist
 	}
-
-	// Create slices up to the next power of two to avoid bounds checks.
-	lits := w.literalFreq[:256]
-	offs := w.offsetFreq[:32]
-	lengths := w.literalFreq[lengthCodesStart:]
-	lengths = lengths[:32]
-	for _, t := range tokens {
-		if t < endBlockMarker {
-			lits[t.literal()]++
-			continue
-		}
-		length := t.length()
-		offset := t.offset()
-		lengths[lengthCode(length)&31]++
-		offs[offsetCode(offset)&31]++
-	}
-
 	// get the number of literals
 	numLiterals = len(w.literalFreq)
 	for w.literalFreq[numLiterals-1] == 0 {
@@ -590,11 +715,14 @@ func (w *huffmanBitWriter) indexTokens(tokens []token) (numLiterals, numOffsets
 		w.offsetFreq[0] = 1
 		numOffsets = 1
 	}
-	w.literalEncoding.generate(w.literalFreq[:maxNumLit], 15)
-	w.offsetEncoding.generate(w.offsetFreq[:offsetCodeCount], 15)
 	return
 }
 
+func (w *huffmanBitWriter) generate(t *tokens) {
+	w.literalEncoding.generate(w.literalFreq[:literalCount], 15)
+	w.offsetEncoding.generate(w.offsetFreq[:offsetCodeCount], 15)
+}
+
 // writeTokens writes a slice of tokens to the output.
 // codes for literal and offset encoding must be supplied.
 func (w *huffmanBitWriter) writeTokens(tokens []token, leCodes, oeCodes []hcode) {
@@ -626,8 +754,19 @@ func (w *huffmanBitWriter) writeTokens(tokens []token, leCodes, oeCodes []hcode)
 		// Write the length
 		length := t.length()
 		lengthCode := lengthCode(length)
-		w.writeCode(lengths[lengthCode&31])
-		extraLengthBits := uint(lengthExtraBits[lengthCode&31])
+		if false {
+			w.writeCode(lengths[lengthCode&31])
+		} else {
+			// inlined
+			c := lengths[lengthCode&31]
+			w.bits |= uint64(c.code) << w.nbits
+			w.nbits += c.len
+			if w.nbits >= 48 {
+				w.writeOutBits()
+			}
+		}
+
+		extraLengthBits := uint16(lengthExtraBits[lengthCode&31])
 		if extraLengthBits > 0 {
 			extraLength := int32(length - lengthBase[lengthCode&31])
 			w.writeBits(extraLength, extraLengthBits)
@@ -635,8 +774,18 @@ func (w *huffmanBitWriter) writeTokens(tokens []token, leCodes, oeCodes []hcode)
 		// Write the offset
 		offset := t.offset()
 		offsetCode := offsetCode(offset)
-		w.writeCode(offs[offsetCode&31])
-		extraOffsetBits := uint(offsetExtraBits[offsetCode&63])
+		if false {
+			w.writeCode(offs[offsetCode&31])
+		} else {
+			// inlined
+			c := offs[offsetCode&31]
+			w.bits |= uint64(c.code) << w.nbits
+			w.nbits += c.len
+			if w.nbits >= 48 {
+				w.writeOutBits()
+			}
+		}
+		extraOffsetBits := uint16(offsetExtraBits[offsetCode&63])
 		if extraOffsetBits > 0 {
 			extraOffset := int32(offset - offsetBase[offsetCode&63])
 			w.writeBits(extraOffset, extraOffsetBits)
@@ -661,75 +810,101 @@ func init() {
 // writeBlockHuff encodes a block of bytes as either
 // Huffman encoded literals or uncompressed bytes if the
 // results only gains very little from compression.
-func (w *huffmanBitWriter) writeBlockHuff(eof bool, input []byte) {
+func (w *huffmanBitWriter) writeBlockHuff(eof bool, input []byte, sync bool) {
 	if w.err != nil {
 		return
 	}
 
 	// Clear histogram
-	for i := range w.literalFreq {
+	for i := range w.literalFreq[:] {
 		w.literalFreq[i] = 0
 	}
+	if !w.lastHuffMan {
+		for i := range w.offsetFreq[:] {
+			w.offsetFreq[i] = 0
+		}
+	}
 
 	// Add everything as literals
-	histogram(input, w.literalFreq)
-
-	w.literalFreq[endBlockMarker] = 1
-
-	const numLiterals = endBlockMarker + 1
-	const numOffsets = 1
-
-	w.literalEncoding.generate(w.literalFreq[:maxNumLit], 15)
-
-	// Figure out smallest code.
-	// Always use dynamic Huffman or Store
-	var numCodegens int
-
-	// Generate codegen and codegenFrequencies, which indicates how to encode
-	// the literalEncoding and the offsetEncoding.
-	w.generateCodegen(numLiterals, numOffsets, w.literalEncoding, huffOffset)
-	w.codegenEncoding.generate(w.codegenFreq[:], 7)
-	size, numCodegens := w.dynamicSize(w.literalEncoding, huffOffset, 0)
+	// We have to estimate the header size.
+	// Assume header is around 70 bytes:
+	// https://stackoverflow.com/a/25454430
+	const guessHeaderSizeBits = 70 * 8
+	estBits := histogramSize(input, w.literalFreq[:], !eof && !sync)
+	estBits += w.lastHeader + len(input)/32
+	if w.lastHeader == 0 {
+		estBits += guessHeaderSizeBits
+	}
+	estBits += estBits >> w.logNewTablePenalty
 
 	// Store bytes, if we don't get a reasonable improvement.
-	if ssize, storable := w.storedSize(input); storable && ssize < (size+size>>4) {
+	ssize, storable := w.storedSize(input)
+	if storable && ssize < estBits {
 		w.writeStoredHeader(len(input), eof)
 		w.writeBytes(input)
 		return
 	}
 
-	// Huffman.
-	w.writeDynamicHeader(numLiterals, numOffsets, numCodegens, eof)
+	reuseSize := 0
+	if w.lastHeader > 0 {
+		reuseSize = w.literalEncoding.bitLength(w.literalFreq[:256])
+
+		if estBits < reuseSize {
+			// We owe an EOB
+			w.writeCode(w.literalEncoding.codes[endBlockMarker])
+			w.lastHeader = 0
+		}
+	}
+
+	const numLiterals = endBlockMarker + 1
+	const numOffsets = 1
+	if w.lastHeader == 0 {
+		if !eof && !sync {
+			// Generate a slightly suboptimal tree that can be used for all.
+			fillHist(w.literalFreq[:numLiterals])
+		}
+		w.literalFreq[endBlockMarker] = 1
+		w.literalEncoding.generate(w.literalFreq[:numLiterals], 15)
+
+		// Generate codegen and codegenFrequencies, which indicates how to encode
+		// the literalEncoding and the offsetEncoding.
+		w.generateCodegen(numLiterals, numOffsets, w.literalEncoding, huffOffset)
+		w.codegenEncoding.generate(w.codegenFreq[:], 7)
+		numCodegens := w.codegens()
+
+		// Huffman.
+		w.writeDynamicHeader(numLiterals, numOffsets, numCodegens, eof)
+		w.lastHuffMan = true
+		w.lastHeader, _ = w.headerSize()
+	}
+
 	encoding := w.literalEncoding.codes[:257]
-	n := w.nbytes
 	for _, t := range input {
 		// Bitwriting inlined, ~30% speedup
 		c := encoding[t]
 		w.bits |= uint64(c.code) << w.nbits
-		w.nbits += uint(c.len)
-		if w.nbits < 48 {
-			continue
+		w.nbits += c.len
+		if w.nbits >= 48 {
+			bits := w.bits
+			w.bits >>= 48
+			w.nbits -= 48
+			n := w.nbytes
+			binary.LittleEndian.PutUint64(w.bytes[n:], bits)
+			n += 6
+			if n >= bufferFlushSize {
+				if w.err != nil {
+					n = 0
+					return
+				}
+				w.write(w.bytes[:n])
+				n = 0
+			}
+			w.nbytes = n
 		}
-		// Store 6 bytes
-		bits := w.bits
-		w.bits >>= 48
-		w.nbits -= 48
-		w.bytes[n] = byte(bits)
-		w.bytes[n+1] = byte(bits >> 8)
-		w.bytes[n+2] = byte(bits >> 16)
-		w.bytes[n+3] = byte(bits >> 24)
-		w.bytes[n+4] = byte(bits >> 32)
-		w.bytes[n+5] = byte(bits >> 40)
-		n += 6
-		if n < bufferFlushSize {
-			continue
-		}
-		w.write(w.bytes[:n])
-		if w.err != nil {
-			return // Return early in the event of write failures
-		}
-		n = 0
 	}
-	w.nbytes = n
-	w.writeCode(encoding[endBlockMarker])
+	if eof || sync {
+		w.writeCode(encoding[endBlockMarker])
+		w.lastHeader = 0
+		w.lastHuffMan = false
+	}
 }