1 files changed, 190 insertions, 0 deletions
diff --git a/src/compress/flate/gen.go b/src/compress/flate/gen.go
new file mode 100644
index 000000000..6288ecddd
--- /dev/null
+++ b/src/compress/flate/gen.go
@@ -0,0 +1,190 @@
+// Copyright 2012 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build ignore
+
+// This program generates fixedhuff.go
+// Invoke as
+//
+//	go run gen.go -output fixedhuff.go
+
+package main
+
+import (
+	"bytes"
+	"flag"
+	"fmt"
+	"go/format"
+	"io/ioutil"
+	"log"
+)
+
+var filename = flag.String("output", "fixedhuff.go", "output file name")
+
+const maxCodeLen = 16
+
+// Note: the definition of the huffmanDecoder struct is copied from
+// inflate.go, as it is private to the implementation.
+
+// chunk & 15 is number of bits
+// chunk >> 4 is value, including table link
+
+const (
+	huffmanChunkBits  = 9
+	huffmanNumChunks  = 1 << huffmanChunkBits
+	huffmanCountMask  = 15
+	huffmanValueShift = 4
+)
+
+type huffmanDecoder struct {
+	min      int                      // the minimum code length
+	chunks   [huffmanNumChunks]uint32 // chunks as described above
+	links    [][]uint32               // overflow links
+	linkMask uint32                   // mask the width of the link table
+}
+
+// Initialize Huffman decoding tables from array of code lengths.
+func (h *huffmanDecoder) init(bits []int) bool {
+	// Count number of codes of each length,
+	// compute min and max length.
+	var count [maxCodeLen]int
+	var min, max int
+	for _, n := range bits {
+		if n == 0 {
+			continue
+		}
+		if min == 0 || n < min {
+			min = n
+		}
+		if n > max {
+			max = n
+		}
+		count[n]++
+	}
+	if max == 0 {
+		return false
+	}
+
+	h.min = min
+	var linkBits uint
+	var numLinks int
+	if max > huffmanChunkBits {
+		linkBits = uint(max) - huffmanChunkBits
+		numLinks = 1 << linkBits
+		h.linkMask = uint32(numLinks - 1)
+	}
+	code := 0
+	var nextcode [maxCodeLen]int
+	for i := min; i <= max; i++ {
+		if i == huffmanChunkBits+1 {
+			// create link tables
+			link := code >> 1
+			h.links = make([][]uint32, huffmanNumChunks-link)
+			for j := uint(link); j < huffmanNumChunks; j++ {
+				reverse := int(reverseByte[j>>8]) | int(reverseByte[j&0xff])<<8
+				reverse >>= uint(16 - huffmanChunkBits)
+				off := j - uint(link)
+				h.chunks[reverse] = uint32(off<<huffmanValueShift + uint(i))
+				h.links[off] = make([]uint32, 1<<linkBits)
+			}
+		}
+		n := count[i]
+		nextcode[i] = code
+		code += n
+		code <<= 1
+	}
+
+	for i, n := range bits {
+		if n == 0 {
+			continue
+		}
+		code := nextcode[n]
+		nextcode[n]++
+		chunk := uint32(i<<huffmanValueShift | n)
+		reverse := int(reverseByte[code>>8]) | int(reverseByte[code&0xff])<<8
+		reverse >>= uint(16 - n)
+		if n <= huffmanChunkBits {
+			for off := reverse; off < huffmanNumChunks; off += 1 << uint(n) {
+				h.chunks[off] = chunk
+			}
+		} else {
+			linktab := h.links[h.chunks[reverse&(huffmanNumChunks-1)]>>huffmanValueShift]
+			reverse >>= huffmanChunkBits
+			for off := reverse; off < numLinks; off += 1 << uint(n-huffmanChunkBits) {
+				linktab[off] = chunk
+			}
+		}
+	}
+	return true
+}
+
+func main() {
+	flag.Parse()
+
+	var h huffmanDecoder
+	var bits [288]int
+	initReverseByte()
+	for i := 0; i < 144; i++ {
+		bits[i] = 8
+	}
+	for i := 144; i < 256; i++ {
+		bits[i] = 9
+	}
+	for i := 256; i < 280; i++ {
+		bits[i] = 7
+	}
+	for i := 280; i < 288; i++ {
+		bits[i] = 8
+	}
+	h.init(bits[:])
+
+	var buf bytes.Buffer
+
+	fmt.Fprintf(&buf, `// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.`+"\n\n")
+
+	fmt.Fprintln(&buf, "package flate")
+	fmt.Fprintln(&buf)
+	fmt.Fprintln(&buf, "// autogenerated by go run gen.go -output fixedhuff.go, DO NOT EDIT")
+	fmt.Fprintln(&buf)
+	fmt.Fprintln(&buf, "var fixedHuffmanDecoder = huffmanDecoder{")
+	fmt.Fprintf(&buf, "\t%d,\n", h.min)
+	fmt.Fprintln(&buf, "\t[huffmanNumChunks]uint32{")
+	for i := 0; i < huffmanNumChunks; i++ {
+		if i&7 == 0 {
+			fmt.Fprintf(&buf, "\t\t")
+		} else {
+			fmt.Fprintf(&buf, " ")
+		}
+		fmt.Fprintf(&buf, "0x%04x,", h.chunks[i])
+		if i&7 == 7 {
+			fmt.Fprintln(&buf)
+		}
+	}
+	fmt.Fprintln(&buf, "\t},")
+	fmt.Fprintln(&buf, "\tnil, 0,")
+	fmt.Fprintln(&buf, "}")
+
+	data, err := format.Source(buf.Bytes())
+	if err != nil {
+		log.Fatal(err)
+	}
+	err = ioutil.WriteFile(*filename, data, 0644)
+	if err != nil {
+		log.Fatal(err)
+	}
+}
+
+var reverseByte [256]byte
+
+func initReverseByte() {
+	for x := 0; x < 256; x++ {
+		var result byte
+		for i := uint(0); i < 8; i++ {
+			result |= byte(((x >> i) & 1) << (7 - i))
+		}
+		reverseByte[x] = result
+	}
+}