Fix a bug in fmpz_mod_poly_gcdiv_euclidean, triggered by a new test in

fq_poly (xgcd_euclidean).
flintlib · Jul 7, 2020 · 499d027 · 499d027
1 parent 7628a8e
commit 499d027
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Showing 2 changed files with 16 additions and 4 deletions.
diff --git a/fmpz_mod_poly/gcdinv_euclidean.c b/fmpz_mod_poly/gcdinv_euclidean.c
@@ -68,6 +68,12 @@ slong _fmpz_mod_poly_gcdinv_euclidean(fmpz *G, fmpz *S,
             _fmpz_vec_swap(S, Q, lenQ);
 		    _fmpz_vec_neg(S, S, lenQ);
 
+            for (i = 0; i < lenQ; i++)
+            {
+                if (fmpz_sgn(S + i) < 0)
+                    fmpz_add(S + i, S + i, p);
+            }
+
             for (i = 0; i < 2*lenB; i++)
 		        fmpz_clear(Q + i);
 
@@ -129,6 +135,12 @@ slong _fmpz_mod_poly_gcdinv_euclidean(fmpz *G, fmpz *S,
             _fmpz_vec_swap(G, D, lenD);
             _fmpz_vec_swap(S, U1, lenU1);
 
+            for (i = 0; i < lenU1; i++)
+            {
+                if (fmpz_sgn(S + i) < 0)
+                    fmpz_add(S + i, S + i, p);
+            }
+
             for (i = 0; i < 3*lenB + 2*lenA; i++)
 			   fmpz_clear(W + i);
 

diff --git a/fq_poly_templates/test/t-xgcd_euclidean_f.c b/fq_poly_templates/test/t-xgcd_euclidean_f.c
@@ -97,7 +97,7 @@ main(void)
     /* Special case, arguments share a factor ******************************* */
 
     /* Compare with result from GCD and check correctness */
-    for (i = 0; i < 5 * flint_test_multiplier(); i++)
+    for (i = 0; i < 50 * flint_test_multiplier(); i++)
     {
         TEMPLATE(T, ctx_t) ctx;
         TEMPLATE(T, t) f1, f2;
@@ -117,9 +117,9 @@ main(void)
         TEMPLATE(T, poly_init) (t, ctx);
         TEMPLATE(T, poly_init) (v, ctx);
         TEMPLATE(T, poly_init) (w, ctx);
-        TEMPLATE(T, poly_randtest) (a, state, n_randint(state, 100), ctx);
-        TEMPLATE(T, poly_randtest) (b, state, n_randint(state, 100), ctx);
-        TEMPLATE(T, poly_randtest) (f, state, n_randint(state, 20), ctx);
+        TEMPLATE(T, poly_randtest) (a, state, n_randint(state, 10), ctx);
+        TEMPLATE(T, poly_randtest) (b, state, n_randint(state, 10), ctx);
+        TEMPLATE(T, poly_randtest) (f, state, n_randint(state, 5), ctx);
         TEMPLATE(T, poly_mul) (a, a, f, ctx);
         TEMPLATE(T, poly_mul) (b, b, f, ctx);