static void dxtn_decompress_block(const BYTE *src, BYTE *dst, UINT width, UINT height, UINT depth,
        UINT x_pos, UINT y_pos, UINT z_pos, UINT dst_slice_pitch, UINT64 cur_block, UINT fmt)
{
    UINT64 alpha_block, alpha_index, color_block, color_index;
    const UINT64 *source;
    DWORD *dest;
    DWORD alpha_lookup;
    DWORD bgra;
    DWORD temp;
    DWORD i, x, y;
    WORD color[2];
    BYTE alpha_val, color_val;
    BYTE alpha[8];
    BYTE r[4];
    BYTE g[4];
    BYTE b[4];
    BYTE block_offset;

    /* Block selection section. */
    if (fmt == WINED3DFMT_DXT1)
            block_offset = 8;
    else
            block_offset = 16;

    source = (const UINT64 *)(src + cur_block * block_offset);
    if (fmt == WINED3DFMT_DXT1)
        color_block = source[0];
    else
    {
        alpha_block = source[0];
        color_block = source[1];
    }

    /* Color handling section. */
    color[0] = color_block & 0xffff;
    color[1] = (color_block >> 16) & 0xffff;
    for (i = 0; i < 2; ++i)
    {
        temp = (color[i] >> 11) * 255 + 16;
        r[i] = (temp / 32 + temp) / 32;
        temp = ((color[i] >> 5) & 0x3f) * 255 + 32;
        g[i] = (temp / 64 + temp) / 64;
        temp = (color[i] & 0x1f) * 255 + 16;
        b[i] = (temp / 32 + temp) / 32;
    }

    if (fmt == WINED3DFMT_DXT3 || fmt == WINED3DFMT_DXT5 || color[0] > color[1])
    {
        for (i = 0; i < 2; ++i)
        {
            r[2 + i] = (2 * r[0 + i] + r[1 - i]) / 3;
            g[2 + i] = (2 * g[0 + i] + g[1 - i]) / 3;
            b[2 + i] = (2 * b[0 + i] + b[1 - i]) / 3;
        }
    }
    else if (fmt == WINED3DFMT_DXT1 && color[0] <= color[1])
    {
        r[2] = (r[0] + r[1]) / 2;
        g[2] = (g[0] + g[1]) / 2;
        b[2] = (b[0] + b[1]) / 2;

        r[3] = 0;
        g[3] = 0;
        b[3] = 0;
    }

    /* Alpha handling section. */
    switch (fmt)
    {
        case WINED3DFMT_DXT1:
            alpha_index = 0;
            for (i = 0; i < 8; ++i)
                alpha[i] = 255;
            if (color[0] <= color[1])
                    alpha[3] = 0;
            break;
        case WINED3DFMT_DXT3:
            alpha_index = alpha_block;
            for (i = 0; i < 8; ++i)
                alpha[i] = 0;
            break;
        case WINED3DFMT_DXT5:
            alpha_index = (alpha_block >> 16);
            alpha[0] = alpha_block & 0xff;
            alpha[1] = (alpha_block >> 8) & 0xff;
            if (alpha[0] > alpha[1])
            {
                for (i = 0; i < 6; ++i)
                    alpha[2 + i] = (((6 - i) * alpha[0]) + ((1 + i) * alpha[1])) / 7;
            }
            else if (alpha[0] <= alpha[1])
            {
                for (i = 0; i < 4; ++i)
                    alpha[2 + i] = (((4 - i) * alpha[0]) + ((1 + i) * alpha[1])) / 5;
                alpha[6] = 0;
                alpha[7] = 255;
            }
            break;
        default:
            alpha_index = 0;
            break;
    }

    /* This is the data writing section. */
    color_index = (color_block >> 32) & 0xffffffff;
    dest = (DWORD *)(dst + z_pos * dst_slice_pitch);
    for (y = 0; y < 4; ++y)
    {
        if (y_pos + y >= height)
                break;
        for (x = 0; x < 4; ++x)
        {
            if (x_pos + x >= width)
                break;

            color_val = 0;
            alpha_val = 0;
            bgra = 0;

            color_val = (color_index >> (y * 8));
            color_val = (color_val >> (x * 2)) & 0x3;
            switch (fmt)
            {
                case WINED3DFMT_DXT1:
                    alpha_val = color_val;
                    break;
                case WINED3DFMT_DXT3:
                    alpha_lookup = (alpha_index >> (y * 16)) & 0xffff;
                    alpha_val = (alpha_lookup >> (x * 4)) & 0xf;
                    temp = alpha_val * 255 + 8;
                    alpha[0] = (temp / 16 + temp) / 16;
                    break;
                case WINED3DFMT_DXT5:
                    alpha_lookup = (alpha_index >> (y * 12)) & 0xfff;
                    alpha_val = (alpha_lookup >> (x * 3)) & 0x7;
                    break;
            }
            bgra = ((alpha[alpha_val] << 24) | (r[color_val] << 16) | (g[color_val] << 8) | b[color_val]);
            dest[(y_pos + y) * width + (x_pos + x)] = bgra;
        }
    }
}