/usr/share/gocode/src/rsc.io/qr/png.go is in golang-rsc-qr-dev 0.0~git20161121.48b2ede-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 | // Copyright 2011 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.
package qr
// PNG writer for QR codes.
import (
"bytes"
"encoding/binary"
"hash"
"hash/crc32"
)
// PNG returns a PNG image displaying the code.
//
// PNG uses a custom encoder tailored to QR codes.
// Its compressed size is about 2x away from optimal,
// but it runs about 20x faster than calling png.Encode
// on c.Image().
func (c *Code) PNG() []byte {
var p pngWriter
return p.encode(c)
}
type pngWriter struct {
tmp [16]byte
wctmp [4]byte
buf bytes.Buffer
zlib bitWriter
crc hash.Hash32
}
var pngHeader = []byte("\x89PNG\r\n\x1a\n")
func (w *pngWriter) encode(c *Code) []byte {
scale := c.Scale
siz := c.Size
w.buf.Reset()
// Header
w.buf.Write(pngHeader)
// Header block
binary.BigEndian.PutUint32(w.tmp[0:4], uint32((siz+8)*scale))
binary.BigEndian.PutUint32(w.tmp[4:8], uint32((siz+8)*scale))
w.tmp[8] = 1 // 1-bit
w.tmp[9] = 0 // gray
w.tmp[10] = 0
w.tmp[11] = 0
w.tmp[12] = 0
w.writeChunk("IHDR", w.tmp[:13])
// Comment
w.writeChunk("tEXt", comment)
// Data
w.zlib.writeCode(c)
w.writeChunk("IDAT", w.zlib.bytes.Bytes())
// End
w.writeChunk("IEND", nil)
return w.buf.Bytes()
}
var comment = []byte("Software\x00QR-PNG http://qr.swtch.com/")
func (w *pngWriter) writeChunk(name string, data []byte) {
if w.crc == nil {
w.crc = crc32.NewIEEE()
}
binary.BigEndian.PutUint32(w.wctmp[0:4], uint32(len(data)))
w.buf.Write(w.wctmp[0:4])
w.crc.Reset()
copy(w.wctmp[0:4], name)
w.buf.Write(w.wctmp[0:4])
w.crc.Write(w.wctmp[0:4])
w.buf.Write(data)
w.crc.Write(data)
crc := w.crc.Sum32()
binary.BigEndian.PutUint32(w.wctmp[0:4], crc)
w.buf.Write(w.wctmp[0:4])
}
func (b *bitWriter) writeCode(c *Code) {
const ftNone = 0
b.adler32.Reset()
b.bytes.Reset()
b.nbit = 0
scale := c.Scale
siz := c.Size
// zlib header
b.tmp[0] = 0x78
b.tmp[1] = 0
b.tmp[1] += uint8(31 - (uint16(b.tmp[0])<<8+uint16(b.tmp[1]))%31)
b.bytes.Write(b.tmp[0:2])
// Start flate block.
b.writeBits(1, 1, false) // final block
b.writeBits(1, 2, false) // compressed, fixed Huffman tables
// White border.
// First row.
b.byte(ftNone)
n := (scale*(siz+8) + 7) / 8
b.byte(255)
b.repeat(n-1, 1)
// 4*scale rows total.
b.repeat((4*scale-1)*(1+n), 1+n)
for i := 0; i < 4*scale; i++ {
b.adler32.WriteNByte(ftNone, 1)
b.adler32.WriteNByte(255, n)
}
row := make([]byte, 1+n)
for y := 0; y < siz; y++ {
row[0] = ftNone
j := 1
var z uint8
nz := 0
for x := -4; x < siz+4; x++ {
// Raw data.
for i := 0; i < scale; i++ {
z <<= 1
if !c.Black(x, y) {
z |= 1
}
if nz++; nz == 8 {
row[j] = z
j++
nz = 0
}
}
}
if j < len(row) {
row[j] = z
}
for _, z := range row {
b.byte(z)
}
// Scale-1 copies.
b.repeat((scale-1)*(1+n), 1+n)
b.adler32.WriteN(row, scale)
}
// White border.
// First row.
b.byte(ftNone)
b.byte(255)
b.repeat(n-1, 1)
// 4*scale rows total.
b.repeat((4*scale-1)*(1+n), 1+n)
for i := 0; i < 4*scale; i++ {
b.adler32.WriteNByte(ftNone, 1)
b.adler32.WriteNByte(255, n)
}
// End of block.
b.hcode(256)
b.flushBits()
// adler32
binary.BigEndian.PutUint32(b.tmp[0:], b.adler32.Sum32())
b.bytes.Write(b.tmp[0:4])
}
// A bitWriter is a write buffer for bit-oriented data like deflate.
type bitWriter struct {
bytes bytes.Buffer
bit uint32
nbit uint
tmp [4]byte
adler32 adigest
}
func (b *bitWriter) writeBits(bit uint32, nbit uint, rev bool) {
// reverse, for huffman codes
if rev {
br := uint32(0)
for i := uint(0); i < nbit; i++ {
br |= ((bit >> i) & 1) << (nbit - 1 - i)
}
bit = br
}
b.bit |= bit << b.nbit
b.nbit += nbit
for b.nbit >= 8 {
b.bytes.WriteByte(byte(b.bit))
b.bit >>= 8
b.nbit -= 8
}
}
func (b *bitWriter) flushBits() {
if b.nbit > 0 {
b.bytes.WriteByte(byte(b.bit))
b.nbit = 0
b.bit = 0
}
}
func (b *bitWriter) hcode(v int) {
/*
Lit Value Bits Codes
--------- ---- -----
0 - 143 8 00110000 through
10111111
144 - 255 9 110010000 through
111111111
256 - 279 7 0000000 through
0010111
280 - 287 8 11000000 through
11000111
*/
switch {
case v <= 143:
b.writeBits(uint32(v)+0x30, 8, true)
case v <= 255:
b.writeBits(uint32(v-144)+0x190, 9, true)
case v <= 279:
b.writeBits(uint32(v-256)+0, 7, true)
case v <= 287:
b.writeBits(uint32(v-280)+0xc0, 8, true)
default:
panic("invalid hcode")
}
}
func (b *bitWriter) byte(x byte) {
b.hcode(int(x))
}
func (b *bitWriter) codex(c int, val int, nx uint) {
b.hcode(c + val>>nx)
b.writeBits(uint32(val)&(1<<nx-1), nx, false)
}
func (b *bitWriter) repeat(n, d int) {
for ; n >= 258+3; n -= 258 {
b.repeat1(258, d)
}
if n > 258 {
// 258 < n < 258+3
b.repeat1(10, d)
b.repeat1(n-10, d)
return
}
if n < 3 {
panic("invalid flate repeat")
}
b.repeat1(n, d)
}
func (b *bitWriter) repeat1(n, d int) {
/*
Extra Extra Extra
Code Bits Length(s) Code Bits Lengths Code Bits Length(s)
---- ---- ------ ---- ---- ------- ---- ---- -------
257 0 3 267 1 15,16 277 4 67-82
258 0 4 268 1 17,18 278 4 83-98
259 0 5 269 2 19-22 279 4 99-114
260 0 6 270 2 23-26 280 4 115-130
261 0 7 271 2 27-30 281 5 131-162
262 0 8 272 2 31-34 282 5 163-194
263 0 9 273 3 35-42 283 5 195-226
264 0 10 274 3 43-50 284 5 227-257
265 1 11,12 275 3 51-58 285 0 258
266 1 13,14 276 3 59-66
*/
switch {
case n <= 10:
b.codex(257, n-3, 0)
case n <= 18:
b.codex(265, n-11, 1)
case n <= 34:
b.codex(269, n-19, 2)
case n <= 66:
b.codex(273, n-35, 3)
case n <= 130:
b.codex(277, n-67, 4)
case n <= 257:
b.codex(281, n-131, 5)
case n == 258:
b.hcode(285)
default:
panic("invalid repeat length")
}
/*
Extra Extra Extra
Code Bits Dist Code Bits Dist Code Bits Distance
---- ---- ---- ---- ---- ------ ---- ---- --------
0 0 1 10 4 33-48 20 9 1025-1536
1 0 2 11 4 49-64 21 9 1537-2048
2 0 3 12 5 65-96 22 10 2049-3072
3 0 4 13 5 97-128 23 10 3073-4096
4 1 5,6 14 6 129-192 24 11 4097-6144
5 1 7,8 15 6 193-256 25 11 6145-8192
6 2 9-12 16 7 257-384 26 12 8193-12288
7 2 13-16 17 7 385-512 27 12 12289-16384
8 3 17-24 18 8 513-768 28 13 16385-24576
9 3 25-32 19 8 769-1024 29 13 24577-32768
*/
if d <= 4 {
b.writeBits(uint32(d-1), 5, true)
} else if d <= 32768 {
nbit := uint(16)
for d <= 1<<(nbit-1) {
nbit--
}
v := uint32(d - 1)
v &^= 1 << (nbit - 1) // top bit is implicit
code := uint32(2*nbit - 2) // second bit is low bit of code
code |= v >> (nbit - 2)
v &^= 1 << (nbit - 2)
b.writeBits(code, 5, true)
// rest of bits follow
b.writeBits(uint32(v), nbit-2, false)
} else {
panic("invalid repeat distance")
}
}
func (b *bitWriter) run(v byte, n int) {
if n == 0 {
return
}
b.byte(v)
if n-1 < 3 {
for i := 0; i < n-1; i++ {
b.byte(v)
}
} else {
b.repeat(n-1, 1)
}
}
type adigest struct {
a, b uint32
}
func (d *adigest) Reset() { d.a, d.b = 1, 0 }
const amod = 65521
func aupdate(a, b uint32, pi byte, n int) (aa, bb uint32) {
// TODO(rsc): 6g doesn't do magic multiplies for b %= amod,
// only for b = b%amod.
// invariant: a, b < amod
if pi == 0 {
b += uint32(n%amod) * a
b = b % amod
return a, b
}
// n times:
// a += pi
// b += a
// is same as
// b += n*a + n*(n+1)/2*pi
// a += n*pi
m := uint32(n)
b += (m % amod) * a
b = b % amod
b += (m * (m + 1) / 2) % amod * uint32(pi)
b = b % amod
a += (m % amod) * uint32(pi)
a = a % amod
return a, b
}
func afinish(a, b uint32) uint32 {
return b<<16 | a
}
func (d *adigest) WriteN(p []byte, n int) {
for i := 0; i < n; i++ {
for _, pi := range p {
d.a, d.b = aupdate(d.a, d.b, pi, 1)
}
}
}
func (d *adigest) WriteNByte(pi byte, n int) {
d.a, d.b = aupdate(d.a, d.b, pi, n)
}
func (d *adigest) Sum32() uint32 { return afinish(d.a, d.b) }
|