[bugfix] fix sqrfree(poly) for zero polynomials in disguise.

[ginac.git] / ginac / normal.cpp

diff --git a/ginac/normal.cpp b/ginac/normal.cpp
index 439a644606388ad1f70fc08d1d537f3a7189a7be..a8a1e1eb1bd3f7282418eff3160f2ba1a25114e6 100644 (file)
--- a/ginac/normal.cpp
+++ b/ginac/normal.cpp
@@ -1771,7 +1771,7 @@ ex lcm(const ex &a, const ex &b, bool check_args)
  *  Yun's algorithm.  Used internally by sqrfree().
  *
  *  @param a  multivariate polynomial over Z[X], treated here as univariate
- *            polynomial in x.
+ *            polynomial in x (needs not be expanded).
  *  @param x  variable to factor in
  *  @return   vector of factors sorted in ascending degree */
 static exvector sqrfree_yun(const ex &a, const symbol &x)
@@ -1780,6 +1780,9 @@ static exvector sqrfree_yun(const ex &a, const symbol &x)
        ex w = a;
        ex z = w.diff(x);
        ex g = gcd(w, z);
+       if (g.is_zero()) {
+               return res;
+       }
        if (g.is_equal(_ex1)) {
                res.push_back(a);
                return res;
@@ -1787,6 +1790,9 @@ static exvector sqrfree_yun(const ex &a, const symbol &x)
        ex y;
        do {
                w = quo(w, g, x);
+               if (w.is_zero()) {
+                       return res;
+               }
                y = quo(z, g, x);
                z = y - w.diff(x);
                g = gcd(w, z);
@@ -1798,7 +1804,7 @@ static exvector sqrfree_yun(const ex &a, const symbol &x)
 
 /** Compute a square-free factorization of a multivariate polynomial in Q[X].
  *
- *  @param a  multivariate polynomial over Q[X]
+ *  @param a  multivariate polynomial over Q[X] (needs not be expanded)
  *  @param l  lst of variables to factor in, may be left empty for autodetection
  *  @return   a square-free factorization of \p a.
  *
@@ -1833,8 +1839,8 @@ static exvector sqrfree_yun(const ex &a, const symbol &x)
  */
 ex sqrfree(const ex &a, const lst &l)
 {
-       if (is_exactly_a<numeric>(a) ||     // algorithm does not trap a==0
-           is_a<symbol>(a))        // shortcut
+       if (is_exactly_a<numeric>(a) ||
+           is_a<symbol>(a))        // shortcuts
                return a;
 
        // If no lst of variables to factorize in was specified we have to