* bignum.c (bigmul1_karatsuba): avoid overflow that make assertion

  fail in certain case.  this patch is contributed from Ray Chason
  <chasonr at gmail.com> in personal communication.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@30483 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 6 insertions, 6 deletions

diff --git a/bignum.c b/bignum.c
index 2f804db5df..ede0de6523 100644
--- a/bignum.c
+++ b/bignum.c
@@ -2157,14 +2157,14 @@ bigmul1_karatsuba(VALUE x, VALUE y)
     t3 = bigmul0(xh, yh);
 
     i = xn + yn - n;
-    /* add t3 to middle bytes of the result (z1) */
-    bigadd_core(zds + n, i, BDIGITS(t3), big_real_len(t3), zds + n, i);
+    /* subtract t1 from t3 */
+    bigsub_core(BDIGITS(t3), big_real_len(t3), BDIGITS(t1), t1n, BDIGITS(t3), big_real_len(t3));
 
-    /* subtract t1 from middle bytes of the result (z1) */
-    bigsub_core(zds + n, i, BDIGITS(t1), t1n, zds + n, i);
+    /* subtract t2 from t3; t3 is now the middle term of the product */
+    if (t2 != Qundef) bigsub_core(BDIGITS(t3), big_real_len(t3), BDIGITS(t2), t2n, BDIGITS(t3), big_real_len(t3));
 
-    /* subtract t2 from middle bytes of the result (z1) */
-    if (t2 != Qundef) bigsub_core(zds + n, i, BDIGITS(t2), t2n, zds + n, i);
+    /* add t3 to middle bytes of the result (z1) */
+    bigadd_core(zds + n, i, BDIGITS(t3), big_real_len(t3), zds + n, i);
 
     return z;
 }