mirror of
https://github.com/go-gitea/gitea
synced 2024-12-24 06:25:26 +01:00
265 lines
6.9 KiB
Go
265 lines
6.9 KiB
Go
// 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.
|
|
// Following this function, h is guaranteed to be initialized into a complete
|
|
// tree (i.e., neither over-subscribed nor under-subscribed). The exception is a
|
|
// degenerate case where the tree has only a single symbol with length 1. Empty
|
|
// trees are permitted.
|
|
func (h *huffmanDecoder) init(bits []int) bool {
|
|
// Sanity enables additional runtime tests during Huffman
|
|
// table construction. It's intended to be used during
|
|
// development to supplement the currently ad-hoc unit tests.
|
|
const sanity = false
|
|
|
|
if h.min != 0 {
|
|
*h = huffmanDecoder{}
|
|
}
|
|
|
|
// 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]++
|
|
}
|
|
|
|
// Empty tree. The decompressor.huffSym function will fail later if the tree
|
|
// is used. Technically, an empty tree is only valid for the HDIST tree and
|
|
// not the HCLEN and HLIT tree. However, a stream with an empty HCLEN tree
|
|
// is guaranteed to fail since it will attempt to use the tree to decode the
|
|
// codes for the HLIT and HDIST trees. Similarly, an empty HLIT tree is
|
|
// guaranteed to fail later since the compressed data section must be
|
|
// composed of at least one symbol (the end-of-block marker).
|
|
if max == 0 {
|
|
return true
|
|
}
|
|
|
|
code := 0
|
|
var nextcode [maxCodeLen]int
|
|
for i := min; i <= max; i++ {
|
|
code <<= 1
|
|
nextcode[i] = code
|
|
code += count[i]
|
|
}
|
|
|
|
// Check that the coding is complete (i.e., that we've
|
|
// assigned all 2-to-the-max possible bit sequences).
|
|
// Exception: To be compatible with zlib, we also need to
|
|
// accept degenerate single-code codings. See also
|
|
// TestDegenerateHuffmanCoding.
|
|
if code != 1<<uint(max) && !(code == 1 && max == 1) {
|
|
return false
|
|
}
|
|
|
|
h.min = min
|
|
if max > huffmanChunkBits {
|
|
numLinks := 1 << (uint(max) - huffmanChunkBits)
|
|
h.linkMask = uint32(numLinks - 1)
|
|
|
|
// create link tables
|
|
link := nextcode[huffmanChunkBits+1] >> 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)
|
|
if sanity && h.chunks[reverse] != 0 {
|
|
panic("impossible: overwriting existing chunk")
|
|
}
|
|
h.chunks[reverse] = uint32(off<<huffmanValueShift | (huffmanChunkBits + 1))
|
|
h.links[off] = make([]uint32, numLinks)
|
|
}
|
|
}
|
|
|
|
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 < len(h.chunks); off += 1 << uint(n) {
|
|
// We should never need to overwrite
|
|
// an existing chunk. Also, 0 is
|
|
// never a valid chunk, because the
|
|
// lower 4 "count" bits should be
|
|
// between 1 and 15.
|
|
if sanity && h.chunks[off] != 0 {
|
|
panic("impossible: overwriting existing chunk")
|
|
}
|
|
h.chunks[off] = chunk
|
|
}
|
|
} else {
|
|
j := reverse & (huffmanNumChunks - 1)
|
|
if sanity && h.chunks[j]&huffmanCountMask != huffmanChunkBits+1 {
|
|
// Longer codes should have been
|
|
// associated with a link table above.
|
|
panic("impossible: not an indirect chunk")
|
|
}
|
|
value := h.chunks[j] >> huffmanValueShift
|
|
linktab := h.links[value]
|
|
reverse >>= huffmanChunkBits
|
|
for off := reverse; off < len(linktab); off += 1 << uint(n-huffmanChunkBits) {
|
|
if sanity && linktab[off] != 0 {
|
|
panic("impossible: overwriting existing chunk")
|
|
}
|
|
linktab[off] = chunk
|
|
}
|
|
}
|
|
}
|
|
|
|
if sanity {
|
|
// Above we've sanity checked that we never overwrote
|
|
// an existing entry. Here we additionally check that
|
|
// we filled the tables completely.
|
|
for i, chunk := range h.chunks {
|
|
if chunk == 0 {
|
|
// As an exception, in the degenerate
|
|
// single-code case, we allow odd
|
|
// chunks to be missing.
|
|
if code == 1 && i%2 == 1 {
|
|
continue
|
|
}
|
|
panic("impossible: missing chunk")
|
|
}
|
|
}
|
|
for _, linktab := range h.links {
|
|
for _, chunk := range linktab {
|
|
if chunk == 0 {
|
|
panic("impossible: missing 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[:])
|
|
if h.links != nil {
|
|
log.Fatal("Unexpected links table in fixed Huffman decoder")
|
|
}
|
|
|
|
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
|
|
}
|
|
}
|