DecodedBitStreamParser.java
/*
* Copyright 2009 ZXing authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.zxing.pdf417.decoder;
import com.google.zxing.FormatException;
import com.google.zxing.common.ECIStringBuilder;
import com.google.zxing.common.DecoderResult;
import com.google.zxing.pdf417.PDF417ResultMetadata;
import java.math.BigInteger;
import java.util.Arrays;
/**
* <p>This class contains the methods for decoding the PDF417 codewords.</p>
*
* @author SITA Lab (kevin.osullivan@sita.aero)
* @author Guenther Grau
*/
final class DecodedBitStreamParser {
private enum Mode {
ALPHA,
LOWER,
MIXED,
PUNCT,
ALPHA_SHIFT,
PUNCT_SHIFT
}
private static final int TEXT_COMPACTION_MODE_LATCH = 900;
private static final int BYTE_COMPACTION_MODE_LATCH = 901;
private static final int NUMERIC_COMPACTION_MODE_LATCH = 902;
private static final int BYTE_COMPACTION_MODE_LATCH_6 = 924;
private static final int ECI_USER_DEFINED = 925;
private static final int ECI_GENERAL_PURPOSE = 926;
private static final int ECI_CHARSET = 927;
private static final int BEGIN_MACRO_PDF417_CONTROL_BLOCK = 928;
private static final int BEGIN_MACRO_PDF417_OPTIONAL_FIELD = 923;
private static final int MACRO_PDF417_TERMINATOR = 922;
private static final int MODE_SHIFT_TO_BYTE_COMPACTION_MODE = 913;
private static final int MAX_NUMERIC_CODEWORDS = 15;
private static final int MACRO_PDF417_OPTIONAL_FIELD_FILE_NAME = 0;
private static final int MACRO_PDF417_OPTIONAL_FIELD_SEGMENT_COUNT = 1;
private static final int MACRO_PDF417_OPTIONAL_FIELD_TIME_STAMP = 2;
private static final int MACRO_PDF417_OPTIONAL_FIELD_SENDER = 3;
private static final int MACRO_PDF417_OPTIONAL_FIELD_ADDRESSEE = 4;
private static final int MACRO_PDF417_OPTIONAL_FIELD_FILE_SIZE = 5;
private static final int MACRO_PDF417_OPTIONAL_FIELD_CHECKSUM = 6;
private static final int PL = 25;
private static final int LL = 27;
private static final int AS = 27;
private static final int ML = 28;
private static final int AL = 28;
private static final int PS = 29;
private static final int PAL = 29;
private static final char[] PUNCT_CHARS =
";<>@[\\]_`~!\r\t,:\n-.$/\"|*()?{}'".toCharArray();
private static final char[] MIXED_CHARS =
"0123456789&\r\t,:#-.$/+%*=^".toCharArray();
/**
* Table containing values for the exponent of 900.
* This is used in the numeric compaction decode algorithm.
*/
private static final BigInteger[] EXP900;
static {
EXP900 = new BigInteger[16];
EXP900[0] = BigInteger.ONE;
BigInteger nineHundred = BigInteger.valueOf(900);
EXP900[1] = nineHundred;
for (int i = 2; i < EXP900.length; i++) {
EXP900[i] = EXP900[i - 1].multiply(nineHundred);
}
}
private static final int NUMBER_OF_SEQUENCE_CODEWORDS = 2;
private DecodedBitStreamParser() {
}
static DecoderResult decode(int[] codewords, String ecLevel) throws FormatException {
ECIStringBuilder result = new ECIStringBuilder(codewords.length * 2);
int codeIndex = textCompaction(codewords, 1, result);
PDF417ResultMetadata resultMetadata = new PDF417ResultMetadata();
while (codeIndex < codewords[0]) {
int code = codewords[codeIndex++];
switch (code) {
case TEXT_COMPACTION_MODE_LATCH:
codeIndex = textCompaction(codewords, codeIndex, result);
break;
case BYTE_COMPACTION_MODE_LATCH:
case BYTE_COMPACTION_MODE_LATCH_6:
codeIndex = byteCompaction(code, codewords, codeIndex, result);
break;
case MODE_SHIFT_TO_BYTE_COMPACTION_MODE:
result.append((char) codewords[codeIndex++]);
break;
case NUMERIC_COMPACTION_MODE_LATCH:
codeIndex = numericCompaction(codewords, codeIndex, result);
break;
case ECI_CHARSET:
result.appendECI(codewords[codeIndex++]);
break;
case ECI_GENERAL_PURPOSE:
// Can't do anything with generic ECI; skip its 2 characters
codeIndex += 2;
break;
case ECI_USER_DEFINED:
// Can't do anything with user ECI; skip its 1 character
codeIndex++;
break;
case BEGIN_MACRO_PDF417_CONTROL_BLOCK:
codeIndex = decodeMacroBlock(codewords, codeIndex, resultMetadata);
break;
case BEGIN_MACRO_PDF417_OPTIONAL_FIELD:
case MACRO_PDF417_TERMINATOR:
// Should not see these outside a macro block
throw FormatException.getFormatInstance();
default:
// Default to text compaction. During testing numerous barcodes
// appeared to be missing the starting mode. In these cases defaulting
// to text compaction seems to work.
codeIndex--;
codeIndex = textCompaction(codewords, codeIndex, result);
break;
}
}
if (result.isEmpty() && resultMetadata.getFileId() == null) {
throw FormatException.getFormatInstance();
}
DecoderResult decoderResult = new DecoderResult(null, result.toString(), null, ecLevel);
decoderResult.setOther(resultMetadata);
return decoderResult;
}
@SuppressWarnings("deprecation")
static int decodeMacroBlock(int[] codewords, int codeIndex, PDF417ResultMetadata resultMetadata)
throws FormatException {
if (codeIndex + NUMBER_OF_SEQUENCE_CODEWORDS > codewords[0]) {
// we must have at least two bytes left for the segment index
throw FormatException.getFormatInstance();
}
int[] segmentIndexArray = new int[NUMBER_OF_SEQUENCE_CODEWORDS];
for (int i = 0; i < NUMBER_OF_SEQUENCE_CODEWORDS; i++, codeIndex++) {
segmentIndexArray[i] = codewords[codeIndex];
}
String segmentIndexString = decodeBase900toBase10(segmentIndexArray, NUMBER_OF_SEQUENCE_CODEWORDS);
if (segmentIndexString.isEmpty()) {
resultMetadata.setSegmentIndex(0);
} else {
try {
resultMetadata.setSegmentIndex(Integer.parseInt(segmentIndexString));
} catch (NumberFormatException nfe) {
// too large; bad input?
throw FormatException.getFormatInstance();
}
}
// Decoding the fileId codewords as 0-899 numbers, each 0-filled to width 3. This follows the spec
// (See ISO/IEC 15438:2015 Annex H.6) and preserves all info, but some generators (e.g. TEC-IT) write
// the fileId using text compaction, so in those cases the fileId will appear mangled.
StringBuilder fileId = new StringBuilder();
while (codeIndex < codewords[0] &&
codeIndex < codewords.length &&
codewords[codeIndex] != MACRO_PDF417_TERMINATOR &&
codewords[codeIndex] != BEGIN_MACRO_PDF417_OPTIONAL_FIELD) {
fileId.append(String.format("%03d", codewords[codeIndex]));
codeIndex++;
}
if (fileId.length() == 0) {
// at least one fileId codeword is required (Annex H.2)
throw FormatException.getFormatInstance();
}
resultMetadata.setFileId(fileId.toString());
int optionalFieldsStart = -1;
if (codewords[codeIndex] == BEGIN_MACRO_PDF417_OPTIONAL_FIELD) {
optionalFieldsStart = codeIndex + 1;
}
while (codeIndex < codewords[0]) {
switch (codewords[codeIndex]) {
case BEGIN_MACRO_PDF417_OPTIONAL_FIELD:
codeIndex++;
switch (codewords[codeIndex]) {
case MACRO_PDF417_OPTIONAL_FIELD_FILE_NAME:
ECIStringBuilder fileName = new ECIStringBuilder();
codeIndex = textCompaction(codewords, codeIndex + 1, fileName);
resultMetadata.setFileName(fileName.toString());
break;
case MACRO_PDF417_OPTIONAL_FIELD_SENDER:
ECIStringBuilder sender = new ECIStringBuilder();
codeIndex = textCompaction(codewords, codeIndex + 1, sender);
resultMetadata.setSender(sender.toString());
break;
case MACRO_PDF417_OPTIONAL_FIELD_ADDRESSEE:
ECIStringBuilder addressee = new ECIStringBuilder();
codeIndex = textCompaction(codewords, codeIndex + 1, addressee);
resultMetadata.setAddressee(addressee.toString());
break;
case MACRO_PDF417_OPTIONAL_FIELD_SEGMENT_COUNT:
ECIStringBuilder segmentCount = new ECIStringBuilder();
codeIndex = numericCompaction(codewords, codeIndex + 1, segmentCount);
try {
resultMetadata.setSegmentCount(Integer.parseInt(segmentCount.toString()));
} catch (NumberFormatException nfe) {
throw FormatException.getFormatInstance();
}
break;
case MACRO_PDF417_OPTIONAL_FIELD_TIME_STAMP:
ECIStringBuilder timestamp = new ECIStringBuilder();
codeIndex = numericCompaction(codewords, codeIndex + 1, timestamp);
try {
resultMetadata.setTimestamp(Long.parseLong(timestamp.toString()));
} catch (NumberFormatException nfe) {
throw FormatException.getFormatInstance();
}
break;
case MACRO_PDF417_OPTIONAL_FIELD_CHECKSUM:
ECIStringBuilder checksum = new ECIStringBuilder();
codeIndex = numericCompaction(codewords, codeIndex + 1, checksum);
try {
resultMetadata.setChecksum(Integer.parseInt(checksum.toString()));
} catch (NumberFormatException nfe) {
throw FormatException.getFormatInstance();
}
break;
case MACRO_PDF417_OPTIONAL_FIELD_FILE_SIZE:
ECIStringBuilder fileSize = new ECIStringBuilder();
codeIndex = numericCompaction(codewords, codeIndex + 1, fileSize);
try {
resultMetadata.setFileSize(Long.parseLong(fileSize.toString()));
} catch (NumberFormatException nfe) {
throw FormatException.getFormatInstance();
}
break;
default:
throw FormatException.getFormatInstance();
}
break;
case MACRO_PDF417_TERMINATOR:
codeIndex++;
resultMetadata.setLastSegment(true);
break;
default:
throw FormatException.getFormatInstance();
}
}
// copy optional fields to additional options
if (optionalFieldsStart != -1) {
int optionalFieldsLength = codeIndex - optionalFieldsStart;
if (resultMetadata.isLastSegment()) {
// do not include terminator
optionalFieldsLength--;
}
if (optionalFieldsLength > 0) {
resultMetadata.setOptionalData(Arrays.copyOfRange(codewords,
optionalFieldsStart, optionalFieldsStart + optionalFieldsLength));
}
}
return codeIndex;
}
/**
* Text Compaction mode (see 5.4.1.5) permits all printable ASCII characters to be
* encoded, i.e. values 32 - 126 inclusive in accordance with ISO/IEC 646 (IRV), as
* well as selected control characters.
*
* @param codewords The array of codewords (data + error)
* @param codeIndex The current index into the codeword array.
* @param result The decoded data is appended to the result.
* @return The next index into the codeword array.
*/
private static int textCompaction(int[] codewords, int codeIndex, ECIStringBuilder result) throws FormatException {
// 2 character per codeword
int[] textCompactionData = new int[(codewords[0] - codeIndex) * 2];
// Used to hold the byte compaction value if there is a mode shift
int[] byteCompactionData = new int[(codewords[0] - codeIndex) * 2];
int index = 0;
boolean end = false;
Mode subMode = Mode.ALPHA;
while ((codeIndex < codewords[0]) && !end) {
int code = codewords[codeIndex++];
if (code < TEXT_COMPACTION_MODE_LATCH) {
textCompactionData[index] = code / 30;
textCompactionData[index + 1] = code % 30;
index += 2;
} else {
switch (code) {
case TEXT_COMPACTION_MODE_LATCH:
// reinitialize text compaction mode to alpha sub mode
textCompactionData[index++] = TEXT_COMPACTION_MODE_LATCH;
break;
case BYTE_COMPACTION_MODE_LATCH:
case BYTE_COMPACTION_MODE_LATCH_6:
case NUMERIC_COMPACTION_MODE_LATCH:
case BEGIN_MACRO_PDF417_CONTROL_BLOCK:
case BEGIN_MACRO_PDF417_OPTIONAL_FIELD:
case MACRO_PDF417_TERMINATOR:
codeIndex--;
end = true;
break;
case MODE_SHIFT_TO_BYTE_COMPACTION_MODE:
// The Mode Shift codeword 913 shall cause a temporary
// switch from Text Compaction mode to Byte Compaction mode.
// This switch shall be in effect for only the next codeword,
// after which the mode shall revert to the prevailing sub-mode
// of the Text Compaction mode. Codeword 913 is only available
// in Text Compaction mode; its use is described in 5.4.2.4.
textCompactionData[index] = MODE_SHIFT_TO_BYTE_COMPACTION_MODE;
code = codewords[codeIndex++];
byteCompactionData[index] = code;
index++;
break;
case ECI_CHARSET:
subMode = decodeTextCompaction(textCompactionData, byteCompactionData, index, result, subMode);
result.appendECI(codewords[codeIndex++]);
if (codeIndex > codewords[0]) {
throw FormatException.getFormatInstance();
}
textCompactionData = new int[(codewords[0] - codeIndex) * 2];
byteCompactionData = new int[(codewords[0] - codeIndex) * 2];
index = 0;
break;
}
}
}
decodeTextCompaction(textCompactionData, byteCompactionData, index, result, subMode);
return codeIndex;
}
/**
* The Text Compaction mode includes all the printable ASCII characters
* (i.e. values from 32 to 126) and three ASCII control characters: HT or tab
* (ASCII value 9), LF or line feed (ASCII value 10), and CR or carriage
* return (ASCII value 13). The Text Compaction mode also includes various latch
* and shift characters which are used exclusively within the mode. The Text
* Compaction mode encodes up to 2 characters per codeword. The compaction rules
* for converting data into PDF417 codewords are defined in 5.4.2.2. The sub-mode
* switches are defined in 5.4.2.3.
*
* @param textCompactionData The text compaction data.
* @param byteCompactionData The byte compaction data if there
* was a mode shift.
* @param length The size of the text compaction and byte compaction data.
* @param result The decoded data is appended to the result.
* @param startMode The mode in which decoding starts
* @return The mode in which decoding ended
*/
private static Mode decodeTextCompaction(int[] textCompactionData,
int[] byteCompactionData,
int length,
ECIStringBuilder result,
Mode startMode) {
// Beginning from an initial state
// The default compaction mode for PDF417 in effect at the start of each symbol shall always be Text
// Compaction mode Alpha sub-mode (uppercase alphabetic). A latch codeword from another mode to the Text
// Compaction mode shall always switch to the Text Compaction Alpha sub-mode.
Mode subMode = startMode;
Mode priorToShiftMode = startMode;
Mode latchedMode = startMode;
int i = 0;
while (i < length) {
int subModeCh = textCompactionData[i];
char ch = 0;
switch (subMode) {
case ALPHA:
// Alpha (uppercase alphabetic)
if (subModeCh < 26) {
// Upper case Alpha Character
ch = (char) ('A' + subModeCh);
} else {
switch (subModeCh) {
case 26:
ch = ' ';
break;
case LL:
subMode = Mode.LOWER;
latchedMode = subMode;
break;
case ML:
subMode = Mode.MIXED;
latchedMode = subMode;
break;
case PS:
// Shift to punctuation
priorToShiftMode = subMode;
subMode = Mode.PUNCT_SHIFT;
break;
case MODE_SHIFT_TO_BYTE_COMPACTION_MODE:
result.append((char) byteCompactionData[i]);
break;
case TEXT_COMPACTION_MODE_LATCH:
subMode = Mode.ALPHA;
latchedMode = subMode;
break;
}
}
break;
case LOWER:
// Lower (lowercase alphabetic)
if (subModeCh < 26) {
ch = (char) ('a' + subModeCh);
} else {
switch (subModeCh) {
case 26:
ch = ' ';
break;
case AS:
// Shift to alpha
priorToShiftMode = subMode;
subMode = Mode.ALPHA_SHIFT;
break;
case ML:
subMode = Mode.MIXED;
latchedMode = subMode;
break;
case PS:
// Shift to punctuation
priorToShiftMode = subMode;
subMode = Mode.PUNCT_SHIFT;
break;
case MODE_SHIFT_TO_BYTE_COMPACTION_MODE:
result.append((char) byteCompactionData[i]);
break;
case TEXT_COMPACTION_MODE_LATCH:
subMode = Mode.ALPHA;
latchedMode = subMode;
break;
}
}
break;
case MIXED:
// Mixed (numeric and some punctuation)
if (subModeCh < PL) {
ch = MIXED_CHARS[subModeCh];
} else {
switch (subModeCh) {
case PL:
subMode = Mode.PUNCT;
latchedMode = subMode;
break;
case 26:
ch = ' ';
break;
case LL:
subMode = Mode.LOWER;
latchedMode = subMode;
break;
case AL:
case TEXT_COMPACTION_MODE_LATCH:
subMode = Mode.ALPHA;
latchedMode = subMode;
break;
case PS:
// Shift to punctuation
priorToShiftMode = subMode;
subMode = Mode.PUNCT_SHIFT;
break;
case MODE_SHIFT_TO_BYTE_COMPACTION_MODE:
result.append((char) byteCompactionData[i]);
break;
}
}
break;
case PUNCT:
// Punctuation
if (subModeCh < PAL) {
ch = PUNCT_CHARS[subModeCh];
} else {
switch (subModeCh) {
case PAL:
case TEXT_COMPACTION_MODE_LATCH:
subMode = Mode.ALPHA;
latchedMode = subMode;
break;
case MODE_SHIFT_TO_BYTE_COMPACTION_MODE:
result.append((char) byteCompactionData[i]);
break;
}
}
break;
case ALPHA_SHIFT:
// Restore sub-mode
subMode = priorToShiftMode;
if (subModeCh < 26) {
ch = (char) ('A' + subModeCh);
} else {
switch (subModeCh) {
case 26:
ch = ' ';
break;
case TEXT_COMPACTION_MODE_LATCH:
subMode = Mode.ALPHA;
break;
}
}
break;
case PUNCT_SHIFT:
// Restore sub-mode
subMode = priorToShiftMode;
if (subModeCh < PAL) {
ch = PUNCT_CHARS[subModeCh];
} else {
switch (subModeCh) {
case PAL:
case TEXT_COMPACTION_MODE_LATCH:
subMode = Mode.ALPHA;
break;
case MODE_SHIFT_TO_BYTE_COMPACTION_MODE:
// PS before Shift-to-Byte is used as a padding character,
// see 5.4.2.4 of the specification
result.append((char) byteCompactionData[i]);
break;
}
}
break;
}
if (ch != 0) {
// Append decoded character to result
result.append(ch);
}
i++;
}
return latchedMode;
}
/**
* Byte Compaction mode (see 5.4.3) permits all 256 possible 8-bit byte values to be encoded.
* This includes all ASCII characters value 0 to 127 inclusive and provides for international
* character set support.
*
* @param mode The byte compaction mode i.e. 901 or 924
* @param codewords The array of codewords (data + error)
* @param codeIndex The current index into the codeword array.
* @param result The decoded data is appended to the result.
* @return The next index into the codeword array.
*/
private static int byteCompaction(int mode,
int[] codewords,
int codeIndex,
ECIStringBuilder result) throws FormatException {
boolean end = false;
while (codeIndex < codewords[0] && !end) {
//handle leading ECIs
while (codeIndex < codewords[0] && codewords[codeIndex] == ECI_CHARSET) {
result.appendECI(codewords[++codeIndex]);
codeIndex++;
}
if (codeIndex >= codewords[0] || codewords[codeIndex] >= TEXT_COMPACTION_MODE_LATCH) {
end = true;
} else {
//decode one block of 5 codewords to 6 bytes
long value = 0;
int count = 0;
do {
value = 900 * value + codewords[codeIndex++];
count++;
} while (count < 5 &&
codeIndex < codewords[0] &&
codewords[codeIndex] < TEXT_COMPACTION_MODE_LATCH);
if (count == 5 && (mode == BYTE_COMPACTION_MODE_LATCH_6 ||
codeIndex < codewords[0] &&
codewords[codeIndex] < TEXT_COMPACTION_MODE_LATCH)) {
for (int i = 0; i < 6; i++) {
result.append((byte) (value >> (8 * (5 - i))));
}
} else {
codeIndex -= count;
while ((codeIndex < codewords[0]) && !end) {
int code = codewords[codeIndex++];
if (code < TEXT_COMPACTION_MODE_LATCH) {
result.append((byte) code);
} else if (code == ECI_CHARSET) {
result.appendECI(codewords[codeIndex++]);
} else {
codeIndex--;
end = true;
}
}
}
}
}
return codeIndex;
}
/**
* Numeric Compaction mode (see 5.4.4) permits efficient encoding of numeric data strings.
*
* @param codewords The array of codewords (data + error)
* @param codeIndex The current index into the codeword array.
* @param result The decoded data is appended to the result.
* @return The next index into the codeword array.
*/
private static int numericCompaction(int[] codewords, int codeIndex, ECIStringBuilder result) throws FormatException {
int count = 0;
boolean end = false;
int[] numericCodewords = new int[MAX_NUMERIC_CODEWORDS];
while (codeIndex < codewords[0] && !end) {
int code = codewords[codeIndex++];
if (codeIndex == codewords[0]) {
end = true;
}
if (code < TEXT_COMPACTION_MODE_LATCH) {
numericCodewords[count] = code;
count++;
} else {
switch (code) {
case TEXT_COMPACTION_MODE_LATCH:
case BYTE_COMPACTION_MODE_LATCH:
case BYTE_COMPACTION_MODE_LATCH_6:
case BEGIN_MACRO_PDF417_CONTROL_BLOCK:
case BEGIN_MACRO_PDF417_OPTIONAL_FIELD:
case MACRO_PDF417_TERMINATOR:
case ECI_CHARSET:
codeIndex--;
end = true;
break;
}
}
if ((count % MAX_NUMERIC_CODEWORDS == 0 || code == NUMERIC_COMPACTION_MODE_LATCH || end) && count > 0) {
// Re-invoking Numeric Compaction mode (by using codeword 902
// while in Numeric Compaction mode) serves to terminate the
// current Numeric Compaction mode grouping as described in 5.4.4.2,
// and then to start a new one grouping.
result.append(decodeBase900toBase10(numericCodewords, count));
count = 0;
}
}
return codeIndex;
}
/**
* Convert a list of Numeric Compacted codewords from Base 900 to Base 10.
*
* @param codewords The array of codewords
* @param count The number of codewords
* @return The decoded string representing the Numeric data.
*/
/*
EXAMPLE
Encode the fifteen digit numeric string 000213298174000
Prefix the numeric string with a 1 and set the initial value of
t = 1 000 213 298 174 000
Calculate codeword 0
d0 = 1 000 213 298 174 000 mod 900 = 200
t = 1 000 213 298 174 000 div 900 = 1 111 348 109 082
Calculate codeword 1
d1 = 1 111 348 109 082 mod 900 = 282
t = 1 111 348 109 082 div 900 = 1 234 831 232
Calculate codeword 2
d2 = 1 234 831 232 mod 900 = 632
t = 1 234 831 232 div 900 = 1 372 034
Calculate codeword 3
d3 = 1 372 034 mod 900 = 434
t = 1 372 034 div 900 = 1 524
Calculate codeword 4
d4 = 1 524 mod 900 = 624
t = 1 524 div 900 = 1
Calculate codeword 5
d5 = 1 mod 900 = 1
t = 1 div 900 = 0
Codeword sequence is: 1, 624, 434, 632, 282, 200
Decode the above codewords involves
1 x 900 power of 5 + 624 x 900 power of 4 + 434 x 900 power of 3 +
632 x 900 power of 2 + 282 x 900 power of 1 + 200 x 900 power of 0 = 1000213298174000
Remove leading 1 => Result is 000213298174000
*/
private static String decodeBase900toBase10(int[] codewords, int count) throws FormatException {
BigInteger result = BigInteger.ZERO;
for (int i = 0; i < count; i++) {
result = result.add(EXP900[count - i - 1].multiply(BigInteger.valueOf(codewords[i])));
}
String resultString = result.toString();
if (resultString.charAt(0) != '1') {
throw FormatException.getFormatInstance();
}
return resultString.substring(1);
}
}