diff --git a/ChangeLog b/ChangeLog
index f00aca1f4b..2aaaaac33c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sun Feb 17 09:17:08 2008  Tanaka Akira  <akr@fsij.org>
+
+	* string.c (rb_str_times): reduce loop overhead.
+
 Sun Feb 17 03:37:01 2008  Tanaka Akira  <akr@fsij.org>
 
 	* include/ruby/re.h (struct rmatch_offset): new struct for character
diff --git a/string.c b/string.c
index 109b2f846d..cc39d7269a 100644
--- a/string.c
+++ b/string.c
@@ -762,7 +762,7 @@ VALUE
 rb_str_times(VALUE str, VALUE times)
 {
     VALUE str2;
-    long i, len;
+    long n, len;
 
     len = NUM2LONG(times);
     if (len < 0) {
@@ -773,9 +773,14 @@ rb_str_times(VALUE str, VALUE times)
     }
 
     str2 = rb_str_new5(str, 0, len *= RSTRING_LEN(str));
-    for (i = 0; i < len; i += RSTRING_LEN(str)) {
-	memcpy(RSTRING_PTR(str2) + i,
-	       RSTRING_PTR(str), RSTRING_LEN(str));
+    if (len) {
+        n = RSTRING_LEN(str);
+        memcpy(RSTRING_PTR(str2), RSTRING_PTR(str), n);
+        while (n <= len/2) {
+            memcpy(RSTRING_PTR(str2) + n, RSTRING_PTR(str2), n);
+            n *= 2;
+        }
+        memcpy(RSTRING_PTR(str2) + n, RSTRING_PTR(str2), len-n);
     }
     RSTRING_PTR(str2)[RSTRING_LEN(str2)] = '\0';
     OBJ_INFECT(str2, str);
diff --git a/test/ruby/test_string.rb b/test/ruby/test_string.rb
index b684ca8bd1..711d9ea1f9 100644
--- a/test/ruby/test_string.rb
+++ b/test/ruby/test_string.rb
@@ -174,7 +174,7 @@ class TestString < Test::Unit::TestCase
     s = "a"
     10.times {|i|
       s << s
-      assert_equal("a" * (2<<i), s)
+      assert_equal("a" * (2 << i), s)
     }
   end
 
@@ -1370,4 +1370,13 @@ class TestString < Test::Unit::TestCase
   def test_end_with?
     assert("abc".end_with?("c"))
   end
+
+  def test_times
+    s1 = ''
+    100.times {|n|
+      s2 = "a" * n
+      assert_equal(s1, s2)
+      s1 << 'a'
+    }
+  end
 end