/*
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* Copyright 2013 ZXing authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#import "ZXPDF417CodewordDecoder.h"
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#import "ZXPDF417Common.h"
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static float ZX_PDF417_RATIOS_TABLE[ZX_PDF417_SYMBOL_TABLE_LEN][ZX_PDF417_BARS_IN_MODULE];
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@implementation ZXPDF417CodewordDecoder
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+ (void)initialize {
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if ([self class] != [ZXPDF417CodewordDecoder class]) return;
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// Pre-computes the symbol ratio table.
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for (int i = 0; i < ZX_PDF417_SYMBOL_TABLE_LEN; i++) {
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int currentSymbol = ZX_PDF417_SYMBOL_TABLE[i];
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int currentBit = currentSymbol & 0x1;
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for (int j = 0; j < ZX_PDF417_BARS_IN_MODULE; j++) {
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float size = 0.0f;
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while ((currentSymbol & 0x1) == currentBit) {
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size += 1.0f;
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currentSymbol >>= 1;
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}
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currentBit = currentSymbol & 0x1;
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ZX_PDF417_RATIOS_TABLE[i][ZX_PDF417_BARS_IN_MODULE - j - 1] = size / ZX_PDF417_MODULES_IN_CODEWORD;
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}
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}
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}
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+ (int)decodedValue:(NSArray *)moduleBitCount {
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int decodedValue = [self decodedCodewordValue:[self sampleBitCounts:moduleBitCount]];
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if (decodedValue != -1) {
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return decodedValue;
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}
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return [self closestDecodedValue:moduleBitCount];
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}
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+ (NSArray *)sampleBitCounts:(NSArray *)moduleBitCount {
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float bitCountSum = [ZXPDF417Common bitCountSum:moduleBitCount];
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NSMutableArray *result = [NSMutableArray arrayWithCapacity:ZX_PDF417_BARS_IN_MODULE];
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for (int i = 0; i < ZX_PDF417_BARS_IN_MODULE; i++) {
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[result addObject:@0];
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}
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int bitCountIndex = 0;
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int sumPreviousBits = 0;
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for (int i = 0; i < ZX_PDF417_MODULES_IN_CODEWORD; i++) {
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float sampleIndex =
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bitCountSum / (2 * ZX_PDF417_MODULES_IN_CODEWORD) +
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(i * bitCountSum) / ZX_PDF417_MODULES_IN_CODEWORD;
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if (sumPreviousBits + [moduleBitCount[bitCountIndex] intValue] <= sampleIndex) {
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sumPreviousBits += [moduleBitCount[bitCountIndex] intValue];
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bitCountIndex++;
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}
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result[bitCountIndex] = @([result[bitCountIndex] intValue] + 1);
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}
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return result;
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}
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+ (int)decodedCodewordValue:(NSArray *)moduleBitCount {
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int decodedValue = [self bitValue:moduleBitCount];
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return [ZXPDF417Common codeword:decodedValue] == -1 ? -1 : decodedValue;
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}
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+ (int)bitValue:(NSArray *)moduleBitCount {
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long result = 0;
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for (int i = 0; i < [moduleBitCount count]; i++) {
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for (int bit = 0; bit < [moduleBitCount[i] intValue]; bit++) {
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result = (result << 1) | (i % 2 == 0 ? 1 : 0);
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}
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}
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return (int) result;
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}
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+ (int)closestDecodedValue:(NSArray *)moduleBitCount {
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int bitCountSum = [ZXPDF417Common bitCountSum:moduleBitCount];
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float bitCountRatios[ZX_PDF417_BARS_IN_MODULE];
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for (int i = 0; i < ZX_PDF417_BARS_IN_MODULE; i++) {
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bitCountRatios[i] = [moduleBitCount[i] intValue] / (float) bitCountSum;
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}
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float bestMatchError = MAXFLOAT;
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int bestMatch = -1;
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for (int j = 0; j < ZX_PDF417_SYMBOL_TABLE_LEN; j++) {
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float error = 0.0f;
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float *ratioTableRow = ZX_PDF417_RATIOS_TABLE[j];
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for (int k = 0; k < ZX_PDF417_BARS_IN_MODULE; k++) {
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float diff = ratioTableRow[k] - bitCountRatios[k];
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error += diff * diff;
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if (error >= bestMatchError) {
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break;
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}
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}
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if (error < bestMatchError) {
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bestMatchError = error;
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bestMatch = ZX_PDF417_SYMBOL_TABLE[j];
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}
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}
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return bestMatch;
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}
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@end
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