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BitSource
This commit is contained in:
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/*
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* Copyright 2007 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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package com.google.zxing.common;
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/**
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* <p>This provides an easy abstraction to read bits at a time from a sequence of bytes, where the
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* number of bits read is not often a multiple of 8.</p>
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*
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* <p>This class is thread-safe but not reentrant -- unless the caller modifies the bytes array
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* it passed in, in which case all bets are off.</p>
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*
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* @author Sean Owen
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*/
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public final class BitSource {
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private final byte[] bytes;
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private int byteOffset;
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private int bitOffset;
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/**
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* @param bytes bytes from which this will read bits. Bits will be read from the first byte first.
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* Bits are read within a byte from most-significant to least-significant bit.
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*/
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public BitSource(byte[] bytes) {
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this.bytes = bytes;
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}
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/**
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* @return index of next bit in current byte which would be read by the next call to {@link #readBits(int)}.
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*/
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public int getBitOffset() {
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return bitOffset;
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}
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/**
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* @return index of next byte in input byte array which would be read by the next call to {@link #readBits(int)}.
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*/
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public int getByteOffset() {
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return byteOffset;
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}
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/**
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* @param numBits number of bits to read
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* @return int representing the bits read. The bits will appear as the least-significant
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* bits of the int
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* @throws IllegalArgumentException if numBits isn't in [1,32] or more than is available
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*/
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public int readBits(int numBits) {
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if (numBits < 1 || numBits > 32 || numBits > available()) {
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throw new IllegalArgumentException(String.valueOf(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 (bitOffset > 0) {
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int bitsLeft = 8 - bitOffset;
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int toRead = Math.min(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 = (bytes[byteOffset] & mask) >> bitsToNotRead;
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numBits -= toRead;
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bitOffset += toRead;
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if (bitOffset == 8) {
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bitOffset = 0;
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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) | (bytes[byteOffset] & 0xFF);
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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) | ((bytes[byteOffset] & mask) >> bitsToNotRead);
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bitOffset += numBits;
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}
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}
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return result;
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}
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/**
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* @return number of bits that can be read successfully
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*/
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public int available() {
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return 8 * (bytes.length - byteOffset) - bitOffset;
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}
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}
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@@ -1419,3 +1419,120 @@ pub trait ECIInput {
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fn getECIValue(index: usize) -> u32;
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fn getECIValue(index: usize) -> u32;
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fn haveNCharacters(index: usize, n: usize) -> bool;
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fn haveNCharacters(index: usize, n: usize) -> bool;
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}
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}
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/*
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* Copyright 2007 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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//package com.google.zxing.common;
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/**
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* <p>This provides an easy abstraction to read bits at a time from a sequence of bytes, where the
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* number of bits read is not often a multiple of 8.</p>
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*
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* <p>This class is thread-safe but not reentrant -- unless the caller modifies the bytes array
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* it passed in, in which case all bets are off.</p>
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*
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* @author Sean Owen
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*/
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pub struct BitSource {
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bytes: Vec<u8>,
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byteOffset: usize,
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bitOffset: usize,
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}
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impl BitSource {
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/**
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* @param bytes bytes from which this will read bits. Bits will be read from the first byte first.
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* Bits are read within a byte from most-significant to least-significant bit.
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*/
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pub fn new(bytes: Vec<u8>) -> Self {
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Self {
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bytes,
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byteOffset: 0,
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bitOffset: 0,
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}
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}
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/**
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* @return index of next bit in current byte which would be read by the next call to {@link #readBits(int)}.
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*/
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pub fn getBitOffset(&self) -> usize {
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return self.bitOffset;
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}
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/**
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* @return index of next byte in input byte array which would be read by the next call to {@link #readBits(int)}.
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*/
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pub fn getByteOffset(&self) -> usize {
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return self.byteOffset;
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}
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/**
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* @param numBits number of bits to read
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* @return int representing the bits read. The bits will appear as the least-significant
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* bits of the int
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* @throws IllegalArgumentException if numBits isn't in [1,32] or more than is available
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*/
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pub fn readBits(&self, numBits: usize) -> Result<u32, IllegalArgumentException> {
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if numBits < 1 || numBits > 32 || numBits > self.available() {
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return Err(IllegalArgumentException::new(numBits));
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}
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let result = 0;
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// First, read remainder from current byte
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if self.bitOffset > 0 {
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let bitsLeft = 8 - self.bitOffset;
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let toRead = cmp::min(numBits, bitsLeft);
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let bitsToNotRead = bitsLeft - toRead;
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let mask = (0xFF >> (8 - toRead)) << bitsToNotRead;
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result = (self.bytes[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 += 1;
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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[self.byteOffset] & 0xFF);
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self.byteOffset += 1;
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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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let bitsToNotRead = 8 - numBits;
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let mask = (0xFF >> bitsToNotRead) << bitsToNotRead;
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result =
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(result << numBits) | ((self.bytes[self.byteOffset] & mask) >> bitsToNotRead);
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self.bitOffset += numBits;
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}
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}
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return Ok(result);
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}
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/**
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* @return number of bits that can be read successfully
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*/
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pub fn available(&self) -> u32 {
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return 8 * (self.bytes.len() - self.byteOffset) - self.bitOffset;
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}
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}
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