115 lines
2.6 KiB
C++
115 lines
2.6 KiB
C++
#include <cstdint>
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#include <fstream>
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#include <iostream>
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#include <vector>
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class BitFilter {
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public:
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BitFilter(const std::string& filePath) {
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writer.open(filePath, std::ios_base::binary);
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reader.open(filePath, std::ios_base::binary);
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accumulator = 0;
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bits = 0;
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}
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void write(const std::vector<char>& chars, const uint32_t& startIndex,
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uint32_t bitCount, uint32_t bitsOmittedCount) {
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uint32_t index = startIndex + bitsOmittedCount / 8;
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bitsOmittedCount %= 8;
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while ( bitCount > 0 || bits >= 8 ) {
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while ( bits >= 8 ) {
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bits -= 8;
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writer.put(accumulator >> bits);
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accumulator &= ( 1 << bits ) - 1;
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}
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while ( bits < 8 && bitCount > 0 ) {
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accumulator = ( accumulator << 1 ) |
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( ( ( 128 >> bitsOmittedCount ) & chars[index] ) >> ( 7 - bitsOmittedCount ) );
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bitCount -= 1;
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bits += 1;
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if ( ++bitsOmittedCount == 8 ) {
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bitsOmittedCount = 0;
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index += 1;
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}
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}
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}
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}
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void read(std::vector<char>& chars, const uint32_t& startIndex,
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uint32_t bitCount, uint32_t bitsOmittedCount) {
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uint32_t index = startIndex + bitsOmittedCount / 8;
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bitsOmittedCount %= 8;
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while ( bitCount > 0 ) {
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while ( bits > 0 && bitCount > 0 ) {
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const uint32_t mask = 128 >> bitsOmittedCount;
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if ( ( accumulator & ( 1 << ( bits - 1 ) ) ) > 0 ) {
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chars[index] = chars[index] | mask;
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} else {
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chars[index] = chars[index] & ( ~mask & 0xff );
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}
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bitCount -= 1;
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bits -= 1;
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if ( ++bitsOmittedCount >= 8 ) {
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bitsOmittedCount = 0;
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index += 1;
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}
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}
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if ( bitCount > 0 ) {
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char qq;
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reader.read((&qq), 1);
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accumulator = ( accumulator << 8 ) | qq;
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bits += 8;
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}
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}
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}
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void close_writer() {
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if ( bits != 0 ) {
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accumulator <<= 8 - bits;
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writer.put(accumulator);
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}
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writer.close();
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accumulator = 0;
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bits = 0;
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}
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void close_reader() {
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reader.close();
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accumulator = 0;
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bits = 0;
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}
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private:
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uint32_t accumulator, bits;
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std::ofstream writer;
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std::ifstream reader;
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};
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int main() {
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BitFilter bitFilter("BitwiseIO.dat");
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std::string source = "abcde12345";
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std::vector<char> chars(source.begin(), source.end());
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// For each char in 'chars', write 7 bits omitting the most significant bit
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for ( uint32_t i = 0; i < chars.size(); ++i ) {
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bitFilter.write(chars, i, 7, 1);
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}
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bitFilter.close_writer();
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// Read 7 bits and expand to a char of 'destination' by reconstructing the most significant bit
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std::vector<char> destination(chars.size());
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for ( uint32_t i = 0; i < destination.size(); ++i ) {
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bitFilter.read(destination, i, 7, 1);
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}
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bitFilter.close_reader();
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std::string result(destination.data());
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std::cout << result << std::endl;
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}
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