401 lines
8.5 KiB
Go
401 lines
8.5 KiB
Go
// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package qr
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// PNG writer for QR codes.
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import (
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"bytes"
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"encoding/binary"
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"hash"
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"hash/crc32"
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)
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// PNG returns a PNG image displaying the code.
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//
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// PNG uses a custom encoder tailored to QR codes.
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// Its compressed size is about 2x away from optimal,
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// but it runs about 20x faster than calling png.Encode
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// on c.Image().
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func (c *Code) PNG() []byte {
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var p pngWriter
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return p.encode(c)
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}
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type pngWriter struct {
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tmp [16]byte
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wctmp [4]byte
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buf bytes.Buffer
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zlib bitWriter
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crc hash.Hash32
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}
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var pngHeader = []byte("\x89PNG\r\n\x1a\n")
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func (w *pngWriter) encode(c *Code) []byte {
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scale := c.Scale
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siz := c.Size
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w.buf.Reset()
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// Header
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w.buf.Write(pngHeader)
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// Header block
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binary.BigEndian.PutUint32(w.tmp[0:4], uint32((siz+8)*scale))
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binary.BigEndian.PutUint32(w.tmp[4:8], uint32((siz+8)*scale))
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w.tmp[8] = 1 // 1-bit
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w.tmp[9] = 0 // gray
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w.tmp[10] = 0
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w.tmp[11] = 0
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w.tmp[12] = 0
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w.writeChunk("IHDR", w.tmp[:13])
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// Comment
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w.writeChunk("tEXt", comment)
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// Data
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w.zlib.writeCode(c)
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w.writeChunk("IDAT", w.zlib.bytes.Bytes())
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// End
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w.writeChunk("IEND", nil)
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return w.buf.Bytes()
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}
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var comment = []byte("Software\x00QR-PNG http://qr.swtch.com/")
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func (w *pngWriter) writeChunk(name string, data []byte) {
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if w.crc == nil {
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w.crc = crc32.NewIEEE()
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}
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binary.BigEndian.PutUint32(w.wctmp[0:4], uint32(len(data)))
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w.buf.Write(w.wctmp[0:4])
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w.crc.Reset()
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copy(w.wctmp[0:4], name)
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w.buf.Write(w.wctmp[0:4])
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w.crc.Write(w.wctmp[0:4])
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w.buf.Write(data)
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w.crc.Write(data)
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crc := w.crc.Sum32()
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binary.BigEndian.PutUint32(w.wctmp[0:4], crc)
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w.buf.Write(w.wctmp[0:4])
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}
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func (b *bitWriter) writeCode(c *Code) {
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const ftNone = 0
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b.adler32.Reset()
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b.bytes.Reset()
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b.nbit = 0
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scale := c.Scale
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siz := c.Size
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// zlib header
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b.tmp[0] = 0x78
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b.tmp[1] = 0
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b.tmp[1] += uint8(31 - (uint16(b.tmp[0])<<8+uint16(b.tmp[1]))%31)
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b.bytes.Write(b.tmp[0:2])
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// Start flate block.
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b.writeBits(1, 1, false) // final block
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b.writeBits(1, 2, false) // compressed, fixed Huffman tables
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// White border.
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// First row.
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b.byte(ftNone)
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n := (scale*(siz+8) + 7) / 8
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b.byte(255)
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b.repeat(n-1, 1)
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// 4*scale rows total.
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b.repeat((4*scale-1)*(1+n), 1+n)
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for i := 0; i < 4*scale; i++ {
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b.adler32.WriteNByte(ftNone, 1)
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b.adler32.WriteNByte(255, n)
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}
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row := make([]byte, 1+n)
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for y := 0; y < siz; y++ {
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row[0] = ftNone
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j := 1
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var z uint8
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nz := 0
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for x := -4; x < siz+4; x++ {
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// Raw data.
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for i := 0; i < scale; i++ {
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z <<= 1
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if !c.Black(x, y) {
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z |= 1
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}
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if nz++; nz == 8 {
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row[j] = z
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j++
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nz = 0
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}
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}
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}
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if j < len(row) {
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row[j] = z
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}
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for _, z := range row {
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b.byte(z)
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}
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// Scale-1 copies.
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b.repeat((scale-1)*(1+n), 1+n)
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b.adler32.WriteN(row, scale)
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}
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// White border.
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// First row.
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b.byte(ftNone)
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b.byte(255)
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b.repeat(n-1, 1)
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// 4*scale rows total.
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b.repeat((4*scale-1)*(1+n), 1+n)
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for i := 0; i < 4*scale; i++ {
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b.adler32.WriteNByte(ftNone, 1)
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b.adler32.WriteNByte(255, n)
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}
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// End of block.
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b.hcode(256)
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b.flushBits()
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// adler32
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binary.BigEndian.PutUint32(b.tmp[0:], b.adler32.Sum32())
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b.bytes.Write(b.tmp[0:4])
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}
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// A bitWriter is a write buffer for bit-oriented data like deflate.
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type bitWriter struct {
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bytes bytes.Buffer
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bit uint32
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nbit uint
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tmp [4]byte
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adler32 adigest
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}
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func (b *bitWriter) writeBits(bit uint32, nbit uint, rev bool) {
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// reverse, for huffman codes
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if rev {
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br := uint32(0)
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for i := uint(0); i < nbit; i++ {
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br |= ((bit >> i) & 1) << (nbit - 1 - i)
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}
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bit = br
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}
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b.bit |= bit << b.nbit
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b.nbit += nbit
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for b.nbit >= 8 {
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b.bytes.WriteByte(byte(b.bit))
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b.bit >>= 8
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b.nbit -= 8
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}
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}
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func (b *bitWriter) flushBits() {
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if b.nbit > 0 {
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b.bytes.WriteByte(byte(b.bit))
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b.nbit = 0
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b.bit = 0
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}
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}
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func (b *bitWriter) hcode(v int) {
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/*
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Lit Value Bits Codes
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--------- ---- -----
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0 - 143 8 00110000 through
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10111111
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144 - 255 9 110010000 through
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111111111
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256 - 279 7 0000000 through
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0010111
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280 - 287 8 11000000 through
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11000111
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*/
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switch {
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case v <= 143:
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b.writeBits(uint32(v)+0x30, 8, true)
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case v <= 255:
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b.writeBits(uint32(v-144)+0x190, 9, true)
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case v <= 279:
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b.writeBits(uint32(v-256)+0, 7, true)
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case v <= 287:
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b.writeBits(uint32(v-280)+0xc0, 8, true)
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default:
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panic("invalid hcode")
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}
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}
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func (b *bitWriter) byte(x byte) {
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b.hcode(int(x))
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}
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func (b *bitWriter) codex(c int, val int, nx uint) {
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b.hcode(c + val>>nx)
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b.writeBits(uint32(val)&(1<<nx-1), nx, false)
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}
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func (b *bitWriter) repeat(n, d int) {
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for ; n >= 258+3; n -= 258 {
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b.repeat1(258, d)
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}
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if n > 258 {
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// 258 < n < 258+3
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b.repeat1(10, d)
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b.repeat1(n-10, d)
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return
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}
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if n < 3 {
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panic("invalid flate repeat")
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}
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b.repeat1(n, d)
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}
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func (b *bitWriter) repeat1(n, d int) {
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/*
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Extra Extra Extra
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Code Bits Length(s) Code Bits Lengths Code Bits Length(s)
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---- ---- ------ ---- ---- ------- ---- ---- -------
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257 0 3 267 1 15,16 277 4 67-82
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258 0 4 268 1 17,18 278 4 83-98
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259 0 5 269 2 19-22 279 4 99-114
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260 0 6 270 2 23-26 280 4 115-130
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261 0 7 271 2 27-30 281 5 131-162
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262 0 8 272 2 31-34 282 5 163-194
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263 0 9 273 3 35-42 283 5 195-226
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264 0 10 274 3 43-50 284 5 227-257
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265 1 11,12 275 3 51-58 285 0 258
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266 1 13,14 276 3 59-66
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*/
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switch {
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case n <= 10:
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b.codex(257, n-3, 0)
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case n <= 18:
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b.codex(265, n-11, 1)
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case n <= 34:
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b.codex(269, n-19, 2)
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case n <= 66:
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b.codex(273, n-35, 3)
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case n <= 130:
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b.codex(277, n-67, 4)
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case n <= 257:
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b.codex(281, n-131, 5)
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case n == 258:
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b.hcode(285)
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default:
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panic("invalid repeat length")
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}
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/*
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Extra Extra Extra
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Code Bits Dist Code Bits Dist Code Bits Distance
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---- ---- ---- ---- ---- ------ ---- ---- --------
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0 0 1 10 4 33-48 20 9 1025-1536
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1 0 2 11 4 49-64 21 9 1537-2048
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2 0 3 12 5 65-96 22 10 2049-3072
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3 0 4 13 5 97-128 23 10 3073-4096
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4 1 5,6 14 6 129-192 24 11 4097-6144
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5 1 7,8 15 6 193-256 25 11 6145-8192
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6 2 9-12 16 7 257-384 26 12 8193-12288
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7 2 13-16 17 7 385-512 27 12 12289-16384
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8 3 17-24 18 8 513-768 28 13 16385-24576
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9 3 25-32 19 8 769-1024 29 13 24577-32768
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*/
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if d <= 4 {
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b.writeBits(uint32(d-1), 5, true)
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} else if d <= 32768 {
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nbit := uint(16)
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for d <= 1<<(nbit-1) {
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nbit--
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}
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v := uint32(d - 1)
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v &^= 1 << (nbit - 1) // top bit is implicit
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code := uint32(2*nbit - 2) // second bit is low bit of code
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code |= v >> (nbit - 2)
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v &^= 1 << (nbit - 2)
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b.writeBits(code, 5, true)
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// rest of bits follow
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b.writeBits(uint32(v), nbit-2, false)
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} else {
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panic("invalid repeat distance")
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}
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}
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func (b *bitWriter) run(v byte, n int) {
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if n == 0 {
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return
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}
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b.byte(v)
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if n-1 < 3 {
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for i := 0; i < n-1; i++ {
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b.byte(v)
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}
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} else {
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b.repeat(n-1, 1)
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}
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}
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type adigest struct {
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a, b uint32
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}
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func (d *adigest) Reset() { d.a, d.b = 1, 0 }
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const amod = 65521
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func aupdate(a, b uint32, pi byte, n int) (aa, bb uint32) {
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// TODO(rsc): 6g doesn't do magic multiplies for b %= amod,
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// only for b = b%amod.
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// invariant: a, b < amod
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if pi == 0 {
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b += uint32(n%amod) * a
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b = b % amod
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return a, b
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}
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// n times:
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// a += pi
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// b += a
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// is same as
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// b += n*a + n*(n+1)/2*pi
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// a += n*pi
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m := uint32(n)
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b += (m % amod) * a
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b = b % amod
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b += (m * (m + 1) / 2) % amod * uint32(pi)
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b = b % amod
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a += (m % amod) * uint32(pi)
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a = a % amod
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return a, b
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}
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func afinish(a, b uint32) uint32 {
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return b<<16 | a
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}
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func (d *adigest) WriteN(p []byte, n int) {
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for i := 0; i < n; i++ {
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for _, pi := range p {
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d.a, d.b = aupdate(d.a, d.b, pi, 1)
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}
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}
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}
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func (d *adigest) WriteNByte(pi byte, n int) {
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d.a, d.b = aupdate(d.a, d.b, pi, n)
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}
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func (d *adigest) Sum32() uint32 { return afinish(d.a, d.b) }
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