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encoding.go
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/
encoding.go
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package polishedqr
import (
"bytes"
"regexp"
"strconv"
)
type CharacterSet int
const (
Numeric = iota
Alphanumeric
Bytes
// Kanji not currently supported
)
var numericRE = regexp.MustCompile(`\d+`)
var alphanumericRE = regexp.MustCompile(`[\dA-Z\ $%*+\-.\/:]+`)
func AutodetectCharacterSet(data []byte) CharacterSet {
// Feels hacky, but the most sane way to do this
if bytes.Equal(numericRE.Find(data), data) {
return Numeric
} else if bytes.Equal(alphanumericRE.Find(data), data) {
return Alphanumeric
} else {
return Bytes
}
}
type Bits []uint8
func CharacterCountBitCapacity(mode CharacterSet, version int) (bitCapacity int) {
// Different versions and encodings have different numbers of bits
// in the character count
if version < 10 {
switch mode {
case Numeric:
bitCapacity = 10
case Alphanumeric:
bitCapacity = 9
case Bytes:
bitCapacity = 8
}
} else if version < 27 {
switch mode {
case Numeric:
bitCapacity = 12
case Alphanumeric:
bitCapacity = 11
case Bytes:
bitCapacity = 16
}
} else {
switch mode {
case Numeric:
bitCapacity = 14
case Alphanumeric:
bitCapacity = 13
case Bytes:
bitCapacity = 16
}
}
return
}
func CharacterCount(count int, mode CharacterSet, version int) Bits {
bitCapacity := CharacterCountBitCapacity(mode, version)
var out Bits
for i := bitCapacity - 1; i >= 0; i-- {
// cursed masking
out = append(out, uint8((count&int(1<<i))>>i))
}
return out
}
func ConvertToNumeric(data []byte, version int) Bits {
var b Bits
// Add mode indicator
b = append(b, Bits{0, 0, 0, 1}...)
// Add character count
b = append(b, CharacterCount(len(data), Numeric, version)...)
// Divide into groups of three digits and convert to bits
for i := 0; i < len(data); i += 3 {
// Group digits
var g []byte
if len(data)-i < 3 {
g = data[i:]
} else {
g = data[i : i+3]
}
// Convert group
gi, err := strconv.Atoi(string(g))
if err != nil {
panic(err)
}
// Small groups are encoded in less bits
bc := 10 - 1
if len(g) == 2 {
bc = 7 - 1
} else if len(g) == 1 {
bc = 4 - 1
}
// Add bits
for i := bc; i >= 0; i-- {
b = append(b, uint8((gi&int(1<<i))>>i))
}
}
return b
}
func ConvertToAlphanumeric(data []byte, version int) Bits {
var b Bits
// Add mode indicator
b = append(b, Bits{0, 0, 1, 0}...)
// Add character count
b = append(b, CharacterCount(len(data), Alphanumeric, version)...)
// Divide into groups of three digits and convert to bits
for i := 0; i < len(data); i += 2 {
// Group digits
var g []byte
if len(data)-i < 2 {
g = data[i:]
} else {
g = data[i : i+2]
}
// Convert group
var gi int
if len(g) > 1 {
gi = 45 * alphanumericTable[g[0]]
gi += alphanumericTable[g[1]]
} else {
gi = alphanumericTable[g[0]]
}
// Small groups are encoded in less bits
bc := 11 - 1
if len(g) == 1 {
bc = 6 - 1
}
// Add bits
for i := bc; i >= 0; i-- {
b = append(b, uint8((gi&int(1<<i))>>i))
}
}
return b
}
func ConvertToBytes(data []byte, version int) Bits {
var b Bits
// Add mode indicator
b = append(b, Bits{0, 1, 0, 0}...)
// Add character count
b = append(b, CharacterCount(len(data), Bytes, version)...)
// Convert each byte into bits
for _, v := range data {
for i := 7; i >= 0; i-- {
b = append(b, uint8((v&(1<<i)))>>i)
}
}
return b
}
// I love manually encoding tables into code by hand
var alphanumericTable = map[byte]int{
'0': 0,
'1': 1,
'2': 2,
'3': 3,
'4': 4,
'5': 5,
'6': 6,
'7': 7,
'8': 8,
'9': 9,
'A': 10,
'B': 11,
'C': 12,
'D': 13,
'E': 14,
'F': 15,
'G': 16,
'H': 17,
'I': 18,
'J': 19,
'K': 20,
'L': 21,
'M': 22,
'N': 23,
'O': 24,
'P': 25,
'Q': 26,
'R': 27,
'S': 28,
'T': 29,
'U': 30,
'V': 31,
'W': 32,
'X': 33,
'Y': 34,
'Z': 35,
' ': 36,
'$': 37,
'%': 38,
'*': 39,
'+': 40,
'-': 41,
'.': 42,
'/': 43,
':': 44,
}
var alphanumericTableReverse = reverseMap(alphanumericTable)