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Core barcode encoding/decoding library
/*
* Copyright 2013 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.common.detector.MathUtils;
import com.google.zxing.pdf417.PDF417Common;
/**
* @author Guenther Grau
* @author creatale GmbH ([email protected])
*/
final class PDF417CodewordDecoder {
private static final float[][] RATIOS_TABLE =
new float[PDF417Common.SYMBOL_TABLE.length][PDF417Common.BARS_IN_MODULE];
static {
// Pre-computes the symbol ratio table.
for (int i = 0; i < PDF417Common.SYMBOL_TABLE.length; i++) {
int currentSymbol = PDF417Common.SYMBOL_TABLE[i];
int currentBit = currentSymbol & 0x1;
for (int j = 0; j < PDF417Common.BARS_IN_MODULE; j++) {
float size = 0.0f;
while ((currentSymbol & 0x1) == currentBit) {
size += 1.0f;
currentSymbol >>= 1;
}
currentBit = currentSymbol & 0x1;
RATIOS_TABLE[i][PDF417Common.BARS_IN_MODULE - j - 1] = size / PDF417Common.MODULES_IN_CODEWORD;
}
}
}
private PDF417CodewordDecoder() {
}
static int getDecodedValue(int[] moduleBitCount) {
int decodedValue = getDecodedCodewordValue(sampleBitCounts(moduleBitCount));
if (decodedValue != -1) {
return decodedValue;
}
return getClosestDecodedValue(moduleBitCount);
}
private static int[] sampleBitCounts(int[] moduleBitCount) {
float bitCountSum = MathUtils.sum(moduleBitCount);
int[] result = new int[PDF417Common.BARS_IN_MODULE];
int bitCountIndex = 0;
int sumPreviousBits = 0;
for (int i = 0; i < PDF417Common.MODULES_IN_CODEWORD; i++) {
float sampleIndex =
bitCountSum / (2 * PDF417Common.MODULES_IN_CODEWORD) +
(i * bitCountSum) / PDF417Common.MODULES_IN_CODEWORD;
if (sumPreviousBits + moduleBitCount[bitCountIndex] <= sampleIndex) {
sumPreviousBits += moduleBitCount[bitCountIndex];
bitCountIndex++;
}
result[bitCountIndex]++;
}
return result;
}
private static int getDecodedCodewordValue(int[] moduleBitCount) {
int decodedValue = getBitValue(moduleBitCount);
return PDF417Common.getCodeword(decodedValue) == -1 ? -1 : decodedValue;
}
private static int getBitValue(int[] moduleBitCount) {
long result = 0;
for (int i = 0; i < moduleBitCount.length; i++) {
for (int bit = 0; bit < moduleBitCount[i]; bit++) {
result = (result << 1) | (i % 2 == 0 ? 1 : 0);
}
}
return (int) result;
}
private static int getClosestDecodedValue(int[] moduleBitCount) {
int bitCountSum = MathUtils.sum(moduleBitCount);
float[] bitCountRatios = new float[PDF417Common.BARS_IN_MODULE];
if (bitCountSum > 1) {
for (int i = 0; i < bitCountRatios.length; i++) {
bitCountRatios[i] = moduleBitCount[i] / (float) bitCountSum;
}
}
float bestMatchError = Float.MAX_VALUE;
int bestMatch = -1;
for (int j = 0; j < RATIOS_TABLE.length; j++) {
float error = 0.0f;
float[] ratioTableRow = RATIOS_TABLE[j];
for (int k = 0; k < PDF417Common.BARS_IN_MODULE; k++) {
float diff = ratioTableRow[k] - bitCountRatios[k];
error += diff * diff;
if (error >= bestMatchError) {
break;
}
}
if (error < bestMatchError) {
bestMatchError = error;
bestMatch = PDF417Common.SYMBOL_TABLE[j];
}
}
return bestMatch;
}
}