ALL: Add flint

external/flint-2.4.3/nmod_poly/div_divconquer.c

@@ -0,0 +1,162 @@
+/*=============================================================================
+
+    This file is part of FLINT.
+
+    FLINT is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    FLINT is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with FLINT; if not, write to the Free Software
+    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
+
+=============================================================================*/
+/******************************************************************************
+
+    Copyright (C) 2008, 2009, 2011 William Hart
+    Copyright (C) 2012 Fredrik Johansson
+
+******************************************************************************/
+
+#include <stdlib.h>
+#include <gmp.h>
+#include "flint.h"
+#include "nmod_vec.h"
+#include "nmod_poly.h"
+
+static void
+__nmod_poly_div_divconquer(mp_ptr Q, mp_srcptr A, slong lenA, 
+                             mp_srcptr B, slong lenB, nmod_t mod)
+{
+    if (lenA < 2 * lenB - 1)
+    {
+        /*
+           Convert unbalanced division into a 2 n1 - 1 by n1 division
+         */
+
+        const slong n1 = lenA - lenB + 1;
+        const slong n2 = lenB - n1;
+
+        mp_srcptr p1 = A + n2;
+        mp_srcptr d1 = B + n2;
+        
+        mp_ptr V = _nmod_vec_init(n1 - 1 + NMOD_DIVREM_DC_ITCH(n1, mod));
+        mp_ptr W = V + NMOD_DIVREM_DC_ITCH(n1, mod);
+
+        _nmod_poly_div_divconquer_recursive(Q, W, V, p1, d1, n1, mod);
+
+        _nmod_vec_clear(V);
+    }
+    else  /* lenA = 2 * lenB - 1 */
+    {
+        mp_ptr V = _nmod_vec_init(lenB - 1 + NMOD_DIVREM_DC_ITCH(lenB, mod));
+        mp_ptr W = V + NMOD_DIVREM_DC_ITCH(lenB, mod);
+ 
+        _nmod_poly_div_divconquer_recursive(Q, W, V, A, B, lenB, mod);
+        
+        _nmod_vec_clear(V);
+    }
+}
+
+
+/* needed due to partial overlap */
+static void
+_nmod_vec_sub_dec(mp_ptr a, mp_srcptr b, mp_srcptr c, slong n, nmod_t mod)
+{
+    slong i;
+
+    for (i = n - 1; i >= 0; i--)
+        a[i] = n_submod(b[i], c[i], mod.n);
+}
+
+void
+_nmod_poly_div_divconquer(mp_ptr Q, mp_srcptr A, slong lenA,
+                             mp_srcptr B, slong lenB, nmod_t mod)
+{
+    if (lenA <= 2 * lenB - 1)
+    {
+        __nmod_poly_div_divconquer(Q, A, lenA, B, lenB, mod);
+    }
+    else  /* lenA > 2 * lenB - 1 */
+    {
+        mp_ptr S, T, V, R;
+        slong shift, next, n = 2 * lenB - 1;
+
+        S = _nmod_vec_init(2 * n + (lenB - 1) + NMOD_DIVREM_DC_ITCH(lenB, mod));
+        T = S + n;
+        R = T + n;
+        V = R + (lenB - 1);
+
+        shift = lenA - n;
+        _nmod_vec_set(S, A + shift, n);
+
+        while (lenA >= n)
+        {
+            shift = lenA - n;
+            _nmod_poly_divrem_divconquer_recursive(Q + shift, T, R, V, S, B, lenB, mod);
+            next = FLINT_MIN(lenB, shift);
+            _nmod_vec_sub_dec(S + next, S, T, lenB - 1, mod);
+            _nmod_vec_set(S, A + shift - next, next);
+            lenA -= lenB;
+        }
+
+        if (lenA >= lenB)
+            __nmod_poly_div_divconquer(Q, S, lenA, B, lenB, mod);
+
+        _nmod_vec_clear(S);
+    }
+}
+
+
+void
+nmod_poly_div_divconquer(nmod_poly_t Q,
+                            const nmod_poly_t A, const nmod_poly_t B)
+{
+    nmod_poly_t tQ;
+    mp_ptr q;
+    slong Alen, Blen;
+
+    Blen = B->length;
+
+    if (Blen == 0)
+    {
+        flint_printf("Exception (nmod_poly_div_divconquer). Division by zero.\n");
+        abort();
+    }
+
+    Alen = A->length;
+
+    if (Alen < Blen)
+    {
+        nmod_poly_zero(Q);
+        return;
+    }
+
+    if (Q == A || Q == B)
+    {
+        nmod_poly_init2(tQ, A->mod.n, Alen - Blen + 1);
+        q = tQ->coeffs;
+    }
+    else
+    {
+        nmod_poly_fit_length(Q, Alen - Blen + 1);
+        q = Q->coeffs;
+    }
+
+    _nmod_poly_div_divconquer(q, A->coeffs, Alen,
+                                       B->coeffs, Blen, A->mod);
+
+    if (Q == A || Q == B)
+    {
+        nmod_poly_swap(tQ, Q);
+        nmod_poly_clear(tQ);
+    }
+    
+    Q->length = Alen - Blen + 1;
+}