unsigned char mul(unsigned char b)
{
    unsigned char sub;
    sub=b>=128?((b<<1)^27):(b<<1);//乘0x02
    return sub;
}


void colmix(unsigned char a[16])
{
    unsigned char b[4][4];
    for(int i=0;i<16;i++)
    {
        b[i/4][i%4]=a[i];
    }

    for(int i=0;i<4;i++)
    {
        b[0][i]=mul(b[0][i])^(mul(b[1][i])^b[1][i])^b[2][i]^b[3][i];
        b[1][i]=b[0][i]^mul(b[1][i])^(mul(b[2][i])^b[2][i])^b[3][i];
        b[2][i]=b[0][i]^b[1][i]^mul(b[2][i])^(mul(b[3][i])^b[3][i]);
        b[3][i]=(mul(b[0][i])^b[0][i])^b[1][i]^b[2][i]^mul(b[3][i]);
    }

    for(int i=0;i<16;i++)
    {
        a[i]=b[i/4][i%4];
    }
}