/*
    Copyright (C) 2010 Fredrik Johansson
    Copyright (C) 2020 William Hart
    Copyright (C) 2020 Daniel Schultz

    This file is part of FLINT.

    FLINT is free software: you can redistribute it and/or modify it under
    the terms of the GNU Lesser General Public License (LGPL) as published
    by the Free Software Foundation; either version 3 of the License, or
    (at your option) any later version.  See <https://www.gnu.org/licenses/>.
*/

#include "nmod_mat.h"
#include "thread_support.h"

#if FLINT_USES_BLAS
# include "cblas.h"
#endif

void
nmod_mat_mul(nmod_mat_t C, const nmod_mat_t A, const nmod_mat_t B)
{
    slong m = A->r;
    slong k = A->c;
    slong n = B->c;
    slong min_dim = FLINT_MIN(FLINT_MIN(m, k), n);
    slong cutoff;
    slong flint_num_threads = flint_get_num_threads();

    FLINT_ASSERT(C->r == A->r);
    FLINT_ASSERT(C->c == B->c);
    FLINT_ASSERT(A->c == B->r);

#if FLINT_USES_BLAS
    /*
        tuning is based on several assumptions:
        (1) blas_num_threads >= flint_num_threads.
        (2) nmod_mat_mul_blas (with crt) only beats
            nmod_mat_mul_classical on square multiplications
            of large enough dimension
        (3) if nmod_mat_mul_blas beats nmod_mat_mul_classical on
            square multiplications of size d, then it beats it on
            rectangular muliplications as long as all dimensions are >= d
    */
    if (FLINT_BITS == 64 && min_dim > 100)
    {
        flint_bitcnt_t bits = FLINT_BIT_COUNT(A->mod.n);

        if (FLINT_BIT_COUNT(k) + 2*bits < 53 + 5)
        {
            /* mul_blas definitely avoids the slow crt */
            cutoff = 100;
        }
        else if (flint_num_threads > 1)
        {
            /* mul_blas with crt is competing against mul_classical_threaded */
            bits = FLINT_MAX(bits, 32);
            cutoff = 100 + 5*flint_num_threads*bits/2;
        }
        else
        {
            /* mul_blas with crt is competing against mul_strassen */
            cutoff = 450;
        }

        if (min_dim > cutoff && nmod_mat_mul_blas(C, A, B))
            return;
    }
#endif

    if (C == A || C == B)
    {
        nmod_mat_t T;
        nmod_mat_init(T, m, n, A->mod.n);
        nmod_mat_mul(T, A, B);
        nmod_mat_swap_entrywise(C, T);
        nmod_mat_clear(T);
        return;
    }

    if (FLINT_BITS == 64 && C->mod.n < 2048)
        cutoff = 400;
    else
        cutoff = 200;

    if (flint_num_threads > 1)
	    nmod_mat_mul_classical_threaded(C, A, B);
    else if (min_dim < cutoff)
        nmod_mat_mul_classical(C, A, B);
    else
        nmod_mat_mul_strassen(C, A, B);
}
