Function RecursiveMultiplyBottom

src/cryptlib/integer.cpp:552–574

// B[N] - multiplicant

void RecursiveMultiplyBottom(word *R, word *T, const word *A, const word *B, unsigned int N)
{
    assert(N>=2 && N%2==0);

    if (N==2)
        AtomicMultiplyBottom(R, A[0], A[1], B[0], B[1]);
    else if (N==4)
    {
        AtomicMultiply(R, A[0], A[1], B[0], B[1]);
        AtomicMultiplyBottomAdd(R+2, A[0], A[1], B[2], B[3]);
        AtomicMultiplyBottomAdd(R+2, A[2], A[3], B[0], B[1]);
    }
    else
    {
        const unsigned int N2 = N/2;

        RecursiveMultiply(R, T, A0, B0, N2);
        RecursiveMultiplyBottom(T0, T1, A1, B0, N2);
        Add(R1, R1, T0, N2);
        RecursiveMultiplyBottom(T0, T1, A0, B1, N2);
        Add(R1, R1, T0, N2);
    }
}

// R[N] --- upper half of A*B
// T[2*N] - temporary work space