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decode.go
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decode.go
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// Package rmqr handles rMRQ Codes.
package rmqr
import (
"errors"
"fmt"
"io"
"math/bits"
"github.com/shogo82148/go-imaging/bitmap"
internalbitmap "github.com/shogo82148/qrcode/internal/bitmap"
"github.com/shogo82148/qrcode/internal/bitstream"
"github.com/shogo82148/qrcode/internal/reedsolomon"
)
func DecodeBitmap(img *bitmap.Image) (*QRCode, error) {
binimg := internalbitmap.Import(img)
bounds := img.Bounds()
w := bounds.Dx() - 1
h := bounds.Dy() - 1
version, level, err := decodeFormat(binimg)
if err != nil {
return nil, err
}
used := usedList[version]
binimg.Mask(binimg, used, precomputedMask)
var buf bitstream.Buffer
dy := -1
x, y := w-1, h-5
for {
if !used.BinaryAt(x, y) {
if binimg.BinaryAt(x, y) {
buf.WriteBit(1)
} else {
buf.WriteBit(0)
}
}
x--
if x < 1 { // +1 is for avoiding time pattern
break
}
if !used.BinaryAt(x, y) {
if binimg.BinaryAt(x, y) {
buf.WriteBit(1)
} else {
buf.WriteBit(0)
}
}
x, y = x+1, y+dy
if y < +1 || y > h-1 { // +1 and -1 are for avoiding time pattern
dy *= -1
x, y = x-2, y+dy
}
if x < 1 { // +1 is for avoiding time pattern
break
}
}
// un-interleave
blocks := decodeFromBits(version, level, buf.Bytes())
// error correction
var result []byte
for _, blk := range blocks {
data := append(blk.data, blk.correction...)
if err := reedsolomon.Decode(data, 2); err != nil {
return nil, err
}
result = append(result, data[:len(blk.data)]...)
}
// decode segments
capacity := capacityTable[version][level]
stream := bitstream.NewBuffer(result[:capacity.Data])
segments := make([]Segment, 0)
bitLength := capacity.BitLength
LOOP:
for {
mode, err := stream.ReadBits(3)
if err == io.EOF {
break
}
switch Mode(mode) {
case ModeNumeric:
seg, err := decodeNumber(bitLength, stream)
if err != nil {
return nil, err
}
segments = append(segments, seg)
case ModeAlphanumeric:
seg, err := decodeAlphanumeric(bitLength, stream)
if err != nil {
return nil, err
}
segments = append(segments, seg)
case ModeBytes:
seg, err := decodeBytes(bitLength, stream)
if err != nil {
return nil, err
}
segments = append(segments, seg)
case ModeKanji:
seg, err := decodeKanji(bitLength, stream)
if err != nil {
return nil, err
}
segments = append(segments, seg)
case ModeTerminated:
break LOOP
default:
return nil, fmt.Errorf("rmqr: unknown mode: %d", mode)
}
}
return &QRCode{
Version: version,
Level: level,
Segments: segments,
}, nil
}
func decodeFormat(img *internalbitmap.Image) (Version, Level, error) {
bounds := img.Rect
w := bounds.Dx() - 1
h := bounds.Dy() - 1
// search version info around finder pattern
var rawVersion uint
for i := 0; i < 18; i++ {
if img.BinaryAt(8+i/5, 1+i%5) {
rawVersion |= 1 << i
}
}
version, level, ok := decodeFormat0(rawVersion ^ 0b011111101010110010)
if ok {
return version, level, nil
}
// search version info around sub-finder pattern
rawVersion = 0
for i := 0; i < 15; i++ {
if img.BinaryAt(w-7+i/5, h-5+i%5) {
rawVersion |= 1 << i
}
}
if img.BinaryAt(w-4, h-5) {
rawVersion |= 1 << 15
}
if img.BinaryAt(w-3, h-5) {
rawVersion |= 1 << 16
}
if img.BinaryAt(w-2, h-5) {
rawVersion |= 1 << 17
}
version, level, ok = decodeFormat0(rawVersion ^ 0b100000101001111011)
if ok {
return version, level, nil
}
return 0, 0, errors.New("rmqr: rMRQ not found")
}
func decodeFormat0(data uint) (Version, Level, bool) {
var idx, min int
min = bits.OnesCount(encodedVersion[0] ^ data)
for i, v := range encodedVersion {
diff := bits.OnesCount(v ^ data)
if diff < min {
idx = i
min = diff
}
}
if min >= 3 {
return 0, 0, false
}
return Version(idx & 0x1f), Level((idx >> 5) & 1), true
}
func decodeFromBits(version Version, level Level, buf []byte) []block {
capacity := capacityTable[version][level]
blocks := []block{}
for _, blockCapacity := range capacity.Blocks {
for i := 0; i < blockCapacity.Num; i++ {
blocks = append(blocks, block{
data: make([]byte, blockCapacity.Data),
correction: make([]byte, blockCapacity.Total-blockCapacity.Data),
maxError: blockCapacity.MaxError,
})
}
}
i := 0
for _, b := range buf[:capacity.Data] {
for {
if i/len(blocks) < len(blocks[i%len(blocks)].data) {
blocks[i%len(blocks)].data[i/len(blocks)] = b
i++
break
}
i++
}
}
i = 0
for _, b := range buf[capacity.Data:capacity.Total] {
for {
if i/len(blocks) < len(blocks[i%len(blocks)].correction) {
blocks[i%len(blocks)].correction[i/len(blocks)] = b
i++
break
}
i++
}
}
return blocks
}
func decodeNumber(bitLength [5]int, buf *bitstream.Buffer) (Segment, error) {
n := bitLength[ModeNumeric]
length, err := buf.ReadBits(n)
if err != nil {
return Segment{}, err
}
data := make([]byte, length)
if err := bitstream.DecodeNumeric(buf, data); err != nil {
return Segment{}, err
}
return Segment{
Mode: ModeNumeric,
Data: data,
}, nil
}
func decodeAlphanumeric(bitLength [5]int, buf *bitstream.Buffer) (Segment, error) {
n := bitLength[ModeAlphanumeric]
length, err := buf.ReadBits(n)
if err != nil {
return Segment{}, err
}
data := make([]byte, length)
if err := bitstream.DecodeAlphanumeric(buf, data); err != nil {
return Segment{}, err
}
return Segment{
Mode: ModeAlphanumeric,
Data: data,
}, nil
}
func decodeBytes(bitLength [5]int, buf *bitstream.Buffer) (Segment, error) {
n := bitLength[ModeBytes]
length, err := buf.ReadBits(n)
if err != nil {
return Segment{}, err
}
data := make([]byte, length)
if err := bitstream.DecodeBytes(buf, data); err != nil {
return Segment{}, err
}
return Segment{
Mode: ModeBytes,
Data: data,
}, nil
}
func decodeKanji(bitLength [5]int, buf *bitstream.Buffer) (Segment, error) {
n := bitLength[ModeKanji]
length, err := buf.ReadBits(n)
if err != nil {
return Segment{}, err
}
data, err := bitstream.DecodeKanji(buf, int(length))
if err != nil {
return Segment{}, err
}
return Segment{
Mode: ModeKanji,
Data: data,
}, nil
}