Task: Bitwise IO
C: #include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>

typedef uint8_t byte;
typedef struct {
    FILE *fp;
    uint32_t accu;
    int bits;
} bit_io_t, *bit_filter;

bit_filter b_attach(FILE *f)
{
    bit_filter b = malloc(sizeof(bit_io_t));
    b->bits = b->accu = 0;
    b->fp = f;
    return b;
}

void b_write(byte *buf, size_t n_bits, size_t shift, bit_filter bf)
{
    uint32_t accu = bf->accu;
    int bits = bf->bits;

    buf += shift / 8;
    shift %= 8;

    while (n_bits || bits >= 8) {
        while (bits >= 8) {
            bits -= 8;
            fputc(accu >> bits, bf->fp);
            accu &= (1 << bits) - 1;
        }
        while (bits < 8 && n_bits) {
            accu = (accu << 1) | (((128 >> shift) & *buf) >> (7 - shift));
            --n_bits;
            bits++;
            if (++shift == 8) {
                shift = 0;
                buf++;
            }
        }
    }
    bf->accu = accu;
    bf->bits = bits;
}

size_t b_read(byte *buf, size_t n_bits, size_t shift, bit_filter bf)
{
    uint32_t accu = bf->accu;
    int bits = bf->bits;
    int mask, i = 0;

    buf += shift / 8;
    shift %= 8;

    while (n_bits) {
        while (bits && n_bits) {
            mask = 128 >> shift;
            if (accu & (1 << (bits - 1))) *buf |= mask;
            else *buf &= ~mask;

            n_bits--;
            bits--;

            if (++shift >= 8) {
                shift = 0;
                buf++;
            }
        }
        if (!n_bits) break;
        accu = (accu << 8) | fgetc(bf->fp);
        bits += 8;
    }
    bf->accu = accu;
    bf->bits = bits;

    return i;
}

void b_detach(bit_filter bf)
{
    if (bf->bits) {
        bf->accu <<= 8 - bf->bits;
        fputc(bf->accu, bf->fp);
    }
    free(bf);
}

int main()
{
    unsigned char s[] = "abcdefghijk";
    unsigned char s2[11] = {0};
    int i;

    FILE *f = fopen("test.bin", "wb");
    bit_filter b = b_attach(f);
    
    for (i = 0; i < 10; i++) b_write(s + i, 7, 1, b);
    b_detach(b);
    fclose(f);

    
    f = fopen("test.bin", "rb");
    b = b_attach(f);
    for (i = 0; i < 10; i++) b_read(s2 + i, 7, 1, b);
    b_detach(b);
    fclose(f);

    printf("%10s\n", s2); 

    return 0;
}

C#: using System;
using System.IO;

public class BitReader
{
    uint readData = 0;
    int startPosition = 0;
    int endPosition = 0;

    public int InBuffer
    {
        get { return endPosition - startPosition; }
    }

    private Stream stream;

    public Stream BaseStream
    {
        get { return stream; }
    }

    public BitReader(Stream stream)
    {
        this.stream = stream;
    }

    void EnsureData(int bitCount)
    {
        int readBits = bitCount - InBuffer;
        while (readBits > 0)
        {
            int b = BaseStream.ReadByte();

            if (b < 0) throw new InvalidOperationException("Unexpected end of stream");

            readData |= checked((uint)b << endPosition);
            endPosition += 8;
            readBits -= 8;
        }
    }

    public bool ReadBit()
    {
        return Read(1) > 0;
    }

    public int Read(int bitCount)
    {
        EnsureData(bitCount);

        int result = (int)(readData >> startPosition) & ((1 << bitCount) - 1);
        startPosition += bitCount;
        if (endPosition == startPosition)
        {
            endPosition = startPosition = 0;
            readData = 0;
        }
        else if (startPosition >= 8)
        {
            readData >>= startPosition;
            endPosition -= startPosition;
            startPosition = 0;
        }

        return result;
    }

    public void Align()
    {
        endPosition = startPosition = 0;
        readData = 0;
    }
}

public class BitWriter
{
    uint data = 0;
    int dataLength = 0;
    Stream stream;

    public Stream BaseStream
    {
        get { return stream; }
    }

    public int BitsToAligment
    {
        get { return (32 - dataLength) % 8; }
    }

    public BitWriter(Stream stream)
    {
        this.stream = stream;
    }

    public void WriteBit(bool value)
    {
        Write(value ? 1 : 0, 1);
    }

    public void Write(int value, int length)
    {
        uint currentData = data | checked((uint)value << dataLength);
        int currentLength = dataLength + length;
        while (currentLength >= 8)
        {
            BaseStream.WriteByte((byte)currentData);
            currentData >>= 8;
            currentLength -= 8;
        }
        data = currentData;
        dataLength = currentLength;
    }

    public void Align()
    {
        if (dataLength > 0)
        {
            BaseStream.WriteByte((byte)data);

            data = 0;
            dataLength = 0;
        }
    }
}

class Program
{
    static void Main(string[] args)
    {
        MemoryStream ms = new MemoryStream();
        BitWriter writer = new BitWriter(ms);
        writer.WriteBit(true);
        writer.Write(5, 3);
        writer.Write(0x0155, 11);
        writer.Align();

        ms.Position = 0;
        BitReader reader = new BitReader(ms);
        Console.WriteLine(reader.ReadBit());
        Console.WriteLine(reader.Read(3));
        Console.WriteLine(reader.Read(11).ToString("x4"));
        reader.Align();
    }
}