pgcd(), chinrem_gcd(): use appropriate definition of the degree.

[ginac.git] / ginac / polynomial / pgcd.cpp

diff --git a/ginac/polynomial/pgcd.cpp b/ginac/polynomial/pgcd.cpp
index ddc3b8cb109ef7154cbf36f0202d5663954abb34..a33b02d78a7dfc2fdb9fc20818b9c30271c52fb2 100644 (file)
--- a/ginac/polynomial/pgcd.cpp
+++ b/ginac/polynomial/pgcd.cpp
@@ -1,3 +1,25 @@
+/** @file pgcd.cpp
+ *
+ *  GCD for polynomials in prime field. */
+
+/*
+ *  GiNaC Copyright (C) 1999-2010 Johannes Gutenberg University Mainz, Germany
+ *
+ *  This program 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.
+ *
+ *  This program 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 this program; if not, write to the Free Software
+ *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+
 #include "pgcd.h"
 #include "collect_vargs.h"
 #include "smod_helpers.h"
@@ -6,8 +28,7 @@
 #include "newton_interpolate.h"
 #include "divide_in_z_p.h"
 
-namespace GiNaC
-{
+namespace GiNaC {
 
 extern void
 primpart_content(ex& pp, ex& c, ex e, const exvector& vars, const long p);
@@ -59,7 +80,8 @@ ex pgcd(const ex& A, const ex& B, const exvector& vars, const long p)
        const ex lc_gcd = euclid_gcd(AL, BL, mainvar, p);
 
        // The estimate of degree of the gcd of Ab and Bb
-       int gcd_deg = std::min(degree(Aprim, mainvar), degree(Bprim, mainvar));
+       exp_vector_t gcd_deg = std::min(degree_vector(Aprim, restvars),
+                                       degree_vector(Bprim, restvars));
        eval_point_finder::value_type b;
 
        eval_point_finder find_eval_point(p);
@@ -84,8 +106,11 @@ ex pgcd(const ex& A, const ex& B, const exvector& vars, const long p)
                const cln::cl_I correct_lc = smod(lcb_gcd*recip(Cblc, p), p);
                Cb = (Cb*numeric(correct_lc)).smod(pn);
 
+               const exp_vector_t img_gcd_deg = degree_vector(Cb, restvars);
+               // Test for relatively prime polynomials
+               if (zerop(img_gcd_deg))
+                       return cont_gcd;
                // Test for unlucky homomorphisms
-               const int img_gcd_deg = Cb.degree(restvars.back());
                if (img_gcd_deg < gcd_deg) {
                        // The degree decreased, previous homomorphisms were
                        // bad, so we have to start it all over.
@@ -111,8 +136,6 @@ ex pgcd(const ex& A, const ex& B, const exvector& vars, const long p)
                const ex H_lcoeff = lcoeff_wrt(H, restvars);
 
                if (H_lcoeff.is_equal(lc_gcd)) {
-                       if ((Hprev-H).expand().smod(pn).is_zero())
-                               continue;
                        ex C /* primitive part of H */, contH /* dummy */;
                        primpart_content(C, contH, H, vars, p);
                        // Normalize GCD so that leading coefficient is 1
@@ -124,8 +147,6 @@ ex pgcd(const ex& A, const ex& B, const exvector& vars, const long p)
                        if (divide_in_z_p(Aprim, C, dummy1, vars, p) &&
                                        divide_in_z_p(Bprim, C, dummy2, vars, p))
                                return (cont_gcd*C).expand().smod(pn);
-                       else if (img_gcd_deg == 0)
-                               return cont_gcd;
                        // else continue building the candidate
                } 
        } while(true);
@@ -133,4 +154,3 @@ ex pgcd(const ex& A, const ex& B, const exvector& vars, const long p)
 }
 
 } // namespace GiNaC
-