import std.stdio;

int[512] tab;
int mul (byte a, byte b)
{
    ushort x = cast(ushort)(a + b)&511;
    ushort y = cast(ushort)(a - b)&511;
    return tab[x] - tab[y];
}
void main (string[] args)
{
    int failed = 0;
    for (auto i = 0; i < 512; i++)
    {
        int a = i < 256 ? i : i - 512;
        tab[i] = a*a/4;
    }
    for (auto x = -128; x < 128; x++)
    {
        for (auto y = -128; y < 128; y++)
        {
            if (mul (cast (byte)x, cast (byte)y) != x*y)
            {
                writefln ("failed %s %s", x, y);
                failed++;
                goto end;
            }
        }
    }
end:
    if (0 == failed) writeln ("passed!");
}