Function sprs::prod::csr_mul_csr_impl

pub fn csr_mul_csr_impl<N, I>(
    lhs: CsMatViewI<N, I>, 
    rhs: CsMatViewI<N, I>, 
    workspace: &mut [N]
) -> CsMatI<N, I> where
    N: Num + Copy,
    I: SpIndex, 

Actual implementation of CSR-CSR multiplication All other matrix products are implemented in terms of this one.