sw1973.d

// Written in the D programming language

/**
 * Basic mixed sources by Slepian-Wolf in 1973
 */

import std.math : abs;

alias byte  Data;
alias int[] Points;

invariant DataSize         = 7;
invariant Data[DataSize] F = [0b001, 0b010, 0b011, 0b100, 0b101, 0b110, 0b111];

void main()
{
    auto x = 0b0111101;
    auto y = 0b0110101;
    auto m = compressData(x);
    assert(m                 == 7);
    assert(detectError(y, m) == 4);
}

/**
 * 7bit character to 3bit.
 */
private Data compressData(Data x)
{
    Data compressed;
    auto points = searchPoints(x);

    foreach (point; points)
        compressed ^= F[point];

    return compressed;
}

/**
 * Detects error bit as Reciever.
 */
private Data detectError(Data y, Data m)
{
    return abs(compressData(y) - m);
}

/**
 * Searches and collects point of 1 value bit.
 */
private Points searchPoints(Data data)
{
    Points points;

    for (int i; i < DataSize; i++)
        if (data >> i & 0x01)
            points ~= DataSize - i - 1;

    return points.reverse;
}