Function DivideByPower2Mod

src/cryptlib/integer.cpp:1075–1090

// M[N] - modulus

void DivideByPower2Mod(word *R, const word *A, unsigned int k, const word *M, unsigned int N)
{
    CopyWords(R, A, N);

    while (k--)
    {
        if (R[0]%2==0)
            ShiftWordsRightByBits(R, N, 1);
        else
        {
            word carry = Add(R, R, M, N);
            ShiftWordsRightByBits(R, N, 1);
            R[N-1] += carry<<(WORD_BITS-1);
        }
    }
}

// R[N] - result = A*(2^k) mod M
// A[N] - input