/*
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* Copyright 2012 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 "ZXBitSource.h"
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#import "ZXByteArray.h"
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@interface ZXBitSource ()
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@property (nonatomic, strong, readonly) ZXByteArray *bytes;
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@property (nonatomic, assign) int byteOffset;
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@property (nonatomic, assign) int bitOffset;
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@end
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@implementation ZXBitSource
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- (id)initWithBytes:(ZXByteArray *)bytes {
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if (self = [super init]) {
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_bytes = bytes;
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}
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return self;
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}
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- (int)readBits:(int)numBits {
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if (numBits < 1 || numBits > 32 || numBits > self.available) {
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[NSException raise:NSInvalidArgumentException format:@"Invalid number of bits: %d", numBits];
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}
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int result = 0;
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// First, read remainder from current byte
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if (self.bitOffset > 0) {
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int bitsLeft = 8 - self.bitOffset;
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int toRead = numBits < bitsLeft ? numBits : bitsLeft;
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int bitsToNotRead = bitsLeft - toRead;
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int mask = (0xFF >> (8 - toRead)) << bitsToNotRead;
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result = (self.bytes.array[self.byteOffset] & mask) >> bitsToNotRead;
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numBits -= toRead;
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self.bitOffset += toRead;
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if (self.bitOffset == 8) {
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self.bitOffset = 0;
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self.byteOffset++;
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}
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}
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// Next read whole bytes
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if (numBits > 0) {
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while (numBits >= 8) {
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result = (result << 8) | (self.bytes.array[self.byteOffset] & 0xFF);
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self.byteOffset++;
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numBits -= 8;
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}
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// Finally read a partial byte
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if (numBits > 0) {
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int bitsToNotRead = 8 - numBits;
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int mask = (0xFF >> bitsToNotRead) << bitsToNotRead;
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result = (result << numBits) | ((self.bytes.array[self.byteOffset] & mask) >> bitsToNotRead);
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self.bitOffset += numBits;
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}
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}
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return result;
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}
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- (int)available {
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return 8 * (self.bytes.length - self.byteOffset) - self.bitOffset;
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}
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@end
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