nobu	2012-03-18 17:17:50 +0900 (Sun, 18 Mar 2012)

  New Revision: 35081

  http://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=rev&revision=35081

  Log:
    * bignum.c (rb_big_pow): estimate result bit size more precisely.
      [ruby-core:30735][Feature #3429]

  Modified files:
    trunk/ChangeLog
    trunk/bignum.c
    trunk/test/ruby/test_bignum.rb

Index: ChangeLog
===================================================================
--- ChangeLog	(revision 35080)
+++ ChangeLog	(revision 35081)
@@ -1,3 +1,8 @@
+Sun Mar 18 17:17:48 2012  Nobuyoshi Nakada  <nobu@r...>
+
+	* bignum.c (rb_big_pow): estimate result bit size more precisely.
+	  [ruby-core:30735][Feature #3429]
+
 Sun Mar 18 17:17:36 2012  Nobuyoshi Nakada  <nobu@r...>
 
 	* gc.c (free_method_entry_i): method entry may be in
Index: bignum.c
===================================================================
--- bignum.c	(revision 35080)
+++ bignum.c	(revision 35081)
@@ -3095,10 +3095,11 @@
 	else {
 	    VALUE z = 0;
 	    SIGNED_VALUE mask;
-	    const long BIGLEN_LIMIT = 1024*1024 / SIZEOF_BDIGITS;
+	    const long xlen = RBIGNUM_LEN(x) - 1;
+	    const long xbits = ffs(RBIGNUM_DIGITS(x)[xlen]) + SIZEOF_BDIGITS*BITSPERDIG*xlen;
+	    const long BIGLEN_LIMIT = BITSPERDIG*1024*1024;
 
-	    if ((RBIGNUM_LEN(x) > BIGLEN_LIMIT) ||
-		(RBIGNUM_LEN(x) > BIGLEN_LIMIT / yy)) {
+	    if ((xbits > BIGLEN_LIMIT) || (xbits * yy > BIGLEN_LIMIT)) {
 		rb_warn("in a**b, b may be too big");
 		d = (double)yy;
 		break;
Index: test/ruby/test_bignum.rb
===================================================================
--- test/ruby/test_bignum.rb	(revision 35080)
+++ test/ruby/test_bignum.rb	(revision 35081)
@@ -326,6 +326,9 @@
     ### rational changes the behavior of Bignum#**
     #assert_raise(TypeError) { T32**"foo" }
     assert_raise(TypeError, ArgumentError) { T32**"foo" }
+
+    feature3429 = '[ruby-core:30735]'
+    assert_instance_of(Bignum, (2 ** 7830457), feature3429)
   end
 
   def test_and

--
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