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ean13_reader.go
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/
ean13_reader.go
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package oned
import (
"github.com/kaxap/gozxing"
)
// For an EAN-13 barcode, the first digit is represented by the parities used
// to encode the next six digits, according to the table below. For example,
// if the barcode is 5 123456 789012 then the value of the first digit is
// signified by using odd for '1', even for '2', even for '3', odd for '4',
// odd for '5', and even for '6'. See http://en.wikipedia.org/wiki/EAN-13
//
// Parity of next 6 digits
// Digit 0 1 2 3 4 5
// 0 Odd Odd Odd Odd Odd Odd
// 1 Odd Odd Even Odd Even Even
// 2 Odd Odd Even Even Odd Even
// 3 Odd Odd Even Even Even Odd
// 4 Odd Even Odd Odd Even Even
// 5 Odd Even Even Odd Odd Even
// 6 Odd Even Even Even Odd Odd
// 7 Odd Even Odd Even Odd Even
// 8 Odd Even Odd Even Even Odd
// 9 Odd Even Even Odd Even Odd
//
// Note that the encoding for '0' uses the same parity as a UPC barcode. Hence
// a UPC barcode can be converted to an EAN-13 barcode by prepending a 0.
//
// The encoding is represented by the following array, which is a bit pattern
// using Odd = 0 and Even = 1. For example, 5 is represented by:
//
// Odd Even Even Odd Odd Even
// in binary:
// 0 1 1 0 0 1 == 0x19
//
var ean13Reader_FIRST_DIGIT_ENCODINGS = []int{
0x00, 0x0B, 0x0D, 0xE, 0x13, 0x19, 0x1C, 0x15, 0x16, 0x1A,
}
type ean13Reader struct {
*upceanReader
decodeMiddleCounters []int
}
func NewEAN13Reader() gozxing.Reader {
this := &ean13Reader{
decodeMiddleCounters: make([]int, 4),
}
this.upceanReader = newUPCEANReader(this)
return this
}
func (this *ean13Reader) decodeMiddle(row *gozxing.BitArray, startRange []int, resultString []byte) (int, []byte, error) {
counters := this.decodeMiddleCounters
counters[0] = 0
counters[1] = 0
counters[2] = 0
counters[3] = 0
end := row.GetSize()
rowOffset := startRange[1]
lgPatternFound := 0
resultString = append(resultString, '0') // rewrite this after determine.
for x := 0; x < 6 && rowOffset < end; x++ {
bestMatch, e := upceanReader_decodeDigit(row, counters, rowOffset, UPCEANReader_L_AND_G_PATTERNS)
if e != nil {
return 0, resultString, gozxing.WrapNotFoundException(e)
}
resultString = append(resultString, byte('0'+bestMatch%10))
for _, counter := range counters {
rowOffset += counter
}
if bestMatch >= 10 {
lgPatternFound |= 1 << uint(5-x)
}
}
firstDigit, e := ean13Reader_determineFirstDigit(lgPatternFound)
if e != nil {
return 0, resultString, e
}
resultString[0] += firstDigit
middleRange, e := upceanReader_findGuardPattern(row, rowOffset, true, UPCEANReader_MIDDLE_PATTERN)
if e != nil {
return 0, resultString, gozxing.WrapNotFoundException(e)
}
rowOffset = middleRange[1]
for x := 0; x < 6 && rowOffset < end; x++ {
bestMatch, e := upceanReader_decodeDigit(row, counters, rowOffset, UPCEANReader_L_PATTERNS)
if e != nil {
return 0, resultString, gozxing.WrapNotFoundException(e)
}
resultString = append(resultString, byte('0'+bestMatch))
for _, counter := range counters {
rowOffset += counter
}
}
return rowOffset, resultString, nil
}
func (this *ean13Reader) getBarcodeFormat() gozxing.BarcodeFormat {
return gozxing.BarcodeFormat_EAN_13
}
// ean13Reader_determineFirstDigit Based on pattern of odd-even ('L' and 'G') patterns
// used to encoded the explicitly-encoded digits in a barcode,
// determines the implicitly encoded first digit and adds it to the result string.
//
// @param resultString string to insert decoded first digit into
// @param lgPatternFound int whose bits indicates the pattern of odd/even L/G patterns used to
// encode digits
// @throws NotFoundException if first digit cannot be determined
func ean13Reader_determineFirstDigit(lgPatternFound int) (byte, error) {
for d := 0; d < 10; d++ {
if lgPatternFound == ean13Reader_FIRST_DIGIT_ENCODINGS[d] {
return byte(d), nil
}
}
return 0, gozxing.NewNotFoundException()
}
func (this *ean13Reader) decodeEnd(row *gozxing.BitArray, endStart int) ([]int, error) {
return upceanReader_decodeEnd(row, endStart)
}
func (this *ean13Reader) checkChecksum(s string) (bool, error) {
return upceanReader_checkChecksum(s)
}