introduce gcd_pf_mul: gcd helper to handle partially factored expressions.
authorAlexei Sheplyakov <varg@theor.jinr.ru>
Mon, 25 Aug 2008 12:53:47 +0000 (16:53 +0400)
committerJens Vollinga <jensv@nikhef.nl>
Wed, 27 Aug 2008 14:22:59 +0000 (16:22 +0200)
GiNaC tries to avoid expanding expressions while computing GCDs and applies
a number of heuristics. Usually this improves performance, but in some cases
it doesn't. Allow user to switch off heuristics.

Part 3:

Move the code handling products from gcd() into a separate function. This
is *really* only code move, everything else should be considered a bug.

ginac/normal.cpp

index 0af5aad856ee2ba95c66bcecf74528ed116de23b..0cb91001a01ff427bdb353590a3a29210c99c597 100644 (file)
@@ -1419,6 +1419,10 @@ static bool heur_gcd(ex& res, const ex& a, const ex& b, ex *ca, ex *cb,
 // large expressions). At least one of the arguments should be a power.
 static ex gcd_pf_pow(const ex& a, const ex& b, ex* ca, ex* cb, bool check_args);
 
+// gcd helper to handle partially factored polynomials (to avoid expanding
+// large expressions). At least one of the arguments should be a product.
+static ex gcd_pf_mul(const ex& a, const ex& b, ex* ca, ex* cb, bool check_args);
+
 /** Compute GCD (Greatest Common Divisor) of multivariate polynomials a(X)
  *  and b(X) in Z[X]. Optionally also compute the cofactors of a and b,
  *  defined by a = ca * gcd(a, b) and b = cb * gcd(a, b).
@@ -1461,46 +1465,8 @@ ex gcd(const ex &a, const ex &b, ex *ca, ex *cb, bool check_args, unsigned optio
        }
 
        // Partially factored cases (to avoid expanding large expressions)
-       if (is_exactly_a<mul>(a)) {
-               if (is_exactly_a<mul>(b) && b.nops() > a.nops())
-                       goto factored_b;
-factored_a:
-               size_t num = a.nops();
-               exvector g; g.reserve(num);
-               exvector acc_ca; acc_ca.reserve(num);
-               ex part_b = b;
-               for (size_t i=0; i<num; i++) {
-                       ex part_ca, part_cb;
-                       g.push_back(gcd(a.op(i), part_b, &part_ca, &part_cb, check_args));
-                       acc_ca.push_back(part_ca);
-                       part_b = part_cb;
-               }
-               if (ca)
-                       *ca = (new mul(acc_ca))->setflag(status_flags::dynallocated);
-               if (cb)
-                       *cb = part_b;
-               return (new mul(g))->setflag(status_flags::dynallocated);
-       } else if (is_exactly_a<mul>(b)) {
-               if (is_exactly_a<mul>(a) && a.nops() > b.nops())
-                       goto factored_a;
-factored_b:
-               size_t num = b.nops();
-               exvector g; g.reserve(num);
-               exvector acc_cb; acc_cb.reserve(num);
-               ex part_a = a;
-               for (size_t i=0; i<num; i++) {
-                       ex part_ca, part_cb;
-                       g.push_back(gcd(part_a, b.op(i), &part_ca, &part_cb, check_args));
-                       acc_cb.push_back(part_cb);
-                       part_a = part_ca;
-               }
-               if (ca)
-                       *ca = part_a;
-               if (cb)
-                       *cb = (new mul(acc_cb))->setflag(status_flags::dynallocated);
-               return (new mul(g))->setflag(status_flags::dynallocated);
-       }
-
+       if (is_exactly_a<mul>(a) || is_exactly_a<mul>(b))
+               return gcd_pf_mul(a, b, ca, cb, check_args);
 #if FAST_COMPARE
        if (is_exactly_a<power>(a) || is_exactly_a<power>(b))
                return gcd_pf_pow(a, b, ca, cb, check_args);
@@ -1771,6 +1737,49 @@ static ex gcd_pf_pow(const ex& a, const ex& b, ex* ca, ex* cb, bool check_args)
        }
 }
 
+static ex gcd_pf_mul(const ex& a, const ex& b, ex* ca, ex* cb, bool check_args)
+{
+       if (is_exactly_a<mul>(a)) {
+               if (is_exactly_a<mul>(b) && b.nops() > a.nops())
+                       goto factored_b;
+factored_a:
+               size_t num = a.nops();
+               exvector g; g.reserve(num);
+               exvector acc_ca; acc_ca.reserve(num);
+               ex part_b = b;
+               for (size_t i=0; i<num; i++) {
+                       ex part_ca, part_cb;
+                       g.push_back(gcd(a.op(i), part_b, &part_ca, &part_cb, check_args));
+                       acc_ca.push_back(part_ca);
+                       part_b = part_cb;
+               }
+               if (ca)
+                       *ca = (new mul(acc_ca))->setflag(status_flags::dynallocated);
+               if (cb)
+                       *cb = part_b;
+               return (new mul(g))->setflag(status_flags::dynallocated);
+       } else if (is_exactly_a<mul>(b)) {
+               if (is_exactly_a<mul>(a) && a.nops() > b.nops())
+                       goto factored_a;
+factored_b:
+               size_t num = b.nops();
+               exvector g; g.reserve(num);
+               exvector acc_cb; acc_cb.reserve(num);
+               ex part_a = a;
+               for (size_t i=0; i<num; i++) {
+                       ex part_ca, part_cb;
+                       g.push_back(gcd(part_a, b.op(i), &part_ca, &part_cb, check_args));
+                       acc_cb.push_back(part_cb);
+                       part_a = part_ca;
+               }
+               if (ca)
+                       *ca = part_a;
+               if (cb)
+                       *cb = (new mul(acc_cb))->setflag(status_flags::dynallocated);
+               return (new mul(g))->setflag(status_flags::dynallocated);
+       }
+}
+
 /** Compute LCM (Least Common Multiple) of multivariate polynomials in Z[X].
  *
  *  @param a  first multivariate polynomial