* 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

ChangeLog

@@ -2,6 +2,12 @@ Fri Jan  7 00:37:35 2011  Tanaka Akira  <akr@fsij.org>
 
 	* string.c: parenthesize macro arguments.
 
+Thu Jan  6 22:42:02 2011  Yukihiro Matsumoto  <matz@ruby-lang.org>
+
+	* 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.
+
 Thu Jan  6 20:55:49 2011  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* lib/mkmf.rb (create_makefile): ignore rest from first dot from

bignum.c

@@ -2157,15 +2157,15 @@ bigmul1_karatsuba(VALUE x, VALUE y)
     t3 = bigmul0(xh, yh);
 
     i = xn + yn - n;
+    /* subtract t1 from t3 */
+    bigsub_core(BDIGITS(t3), big_real_len(t3), BDIGITS(t1), t1n, BDIGITS(t3), big_real_len(t3));
+
+    /* 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));
+
     /* 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 middle bytes of the result (z1) */
-    bigsub_core(zds + n, i, BDIGITS(t1), t1n, zds + n, i);
-
-    /* subtract t2 from middle bytes of the result (z1) */
-    if (t2 != Qundef) bigsub_core(zds + n, i, BDIGITS(t2), t2n, zds + n, i);
-
     return z;
 }