* Avoid bad choice of main variable in heuristic gcd [Alexei Sheplyakov].

diff --git a/ginac/normal.cpp b/ginac/normal.cpp
index b2a4e8c8d0cfdfe2204799fefe96b2710771cb24..d8252abb02742fd4376fea26eb0988e140118acb 100644 (file)
--- a/ginac/normal.cpp
+++ b/ginac/normal.cpp
@@ -6,7 +6,7 @@
  *  computation, square-free factorization and rational function normalization. */
 
 /*
- *  GiNaC Copyright (C) 1999-2005 Johannes Gutenberg University Mainz, Germany
+ *  GiNaC Copyright (C) 1999-2006 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
@@ -1589,11 +1589,51 @@ factored_b:
                }
        }
 
+       if (is_exactly_a<numeric>(aex)) {
+               numeric bcont = bex.integer_content();
+               numeric g = gcd(ex_to<numeric>(aex), bcont);
+               if (ca)
+                       *ca = ex_to<numeric>(aex)/g;
+               if (cb)
+                       *cb = bex/g;
+               return g;
+       }
+
+       if (is_exactly_a<numeric>(bex)) {
+               numeric acont = aex.integer_content();
+               numeric g = gcd(ex_to<numeric>(bex), acont);
+               if (ca)
+                       *ca = aex/g;
+               if (cb)
+                       *cb = ex_to<numeric>(bex)/g;
+               return g;
+       }
+
        // Gather symbol statistics
        sym_desc_vec sym_stats;
        get_symbol_stats(a, b, sym_stats);
 
-       // The symbol with least degree is our main variable
+       // The symbol with least degree which is contained in both polynomials
+       // is our main variable
+       sym_desc_vec::iterator vari = sym_stats.begin();
+       while ((vari != sym_stats.end()) && 
+              (((vari->ldeg_b == 0) && (vari->deg_b == 0)) ||
+               ((vari->ldeg_a == 0) && (vari->deg_a == 0))))
+               vari++;
+
+       // No common symbols at all, just return 1:
+       if (vari == sym_stats.end()) {
+               // N.B: keep cofactors factored
+               if (ca)
+                       *ca = a;
+               if (cb)
+                       *cb = b;
+               return _ex1;
+       }
+       // move symbols which contained only in one of the polynomials
+       // to the end:
+       rotate(sym_stats.begin(), vari, sym_stats.end());
+
        sym_desc_vec::const_iterator var = sym_stats.begin();
        const ex &x = var->sym;
 
@@ -1607,14 +1647,14 @@ factored_b:
        }
 
        // Try to eliminate variables
-       if (var->deg_a == 0) {
+       if (var->deg_a == 0 && var->deg_b != 0 ) {
                ex bex_u, bex_c, bex_p;
                bex.unitcontprim(x, bex_u, bex_c, bex_p);
                ex g = gcd(aex, bex_c, ca, cb, false);
                if (cb)
                        *cb *= bex_u * bex_p;
                return g;
-       } else if (var->deg_b == 0) {
+       } else if (var->deg_b == 0 && var->deg_a != 0) {
                ex aex_u, aex_c, aex_p;
                aex.unitcontprim(x, aex_u, aex_c, aex_p);
                ex g = gcd(aex_c, bex, ca, cb, false);