akr	2013-07-23 20:16:39 +0900 (Tue, 23 Jul 2013)

  New Revision: 42139

  http://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=rev&revision=42139

  Log:
    * bignum.c (bary_divmod): Add special cases for x < y easily detected
      and nx == 2 && ny == 2.

  Modified files:
    trunk/ChangeLog
    trunk/bignum.c

Index: ChangeLog
===================================================================
--- ChangeLog	(revision 42138)
+++ ChangeLog	(revision 42139)
@@ -1,3 +1,8 @@ https://github.com/ruby/ruby/blob/trunk/ChangeLog#L1
+Tue Jul 23 20:14:55 2013  Tanaka Akira  <akr@f...>
+
+	* bignum.c (bary_divmod): Add special cases for x < y easily detected
+	  and nx == 2 && ny == 2.
+
 Tue Jul 23 19:48:38 2013  Koichi Sasada  <ko1@a...>
 
 	* thread_(pthread|win32).h: rename rb_thread_cond_t to
Index: bignum.c
===================================================================
--- bignum.c	(revision 42138)
+++ bignum.c	(revision 42139)
@@ -5266,12 +5266,29 @@ bary_divmod(BDIGIT *qds, size_t nq, BDIG https://github.com/ruby/ruby/blob/trunk/bignum.c#L5266
         return;
     }
 
-    if (ny == 1) {
+    if (nx < ny || (nx == ny && xds[nx - 1] < yds[ny - 1])) {
+        MEMCPY(rds, xds, BDIGIT, nx);
+        BDIGITS_ZERO(rds+nx, nr-nx);
+        BDIGITS_ZERO(qds, nq);
+    }
+    else if (ny == 1) {
         MEMCPY(qds, xds, BDIGIT, nx);
         BDIGITS_ZERO(qds+nx, nq-nx);
         rds[0] = bigdivrem_single(qds, xds, nx, yds[0]);
         BDIGITS_ZERO(rds+1, nr-1);
     }
+    else if (nx == 2 && ny == 2) {
+        BDIGIT_DBL x = xds[0] | BIGUP(xds[1]);
+        BDIGIT_DBL y = yds[0] | BIGUP(yds[1]);
+        BDIGIT_DBL q = x / y;
+        BDIGIT_DBL r = x % y;
+        qds[0] = BIGLO(q);
+        qds[1] = BIGLO(BIGDN(q));
+        BDIGITS_ZERO(qds+2, nq-2);
+        rds[0] = BIGLO(r);
+        rds[1] = BIGLO(BIGDN(r));
+        BDIGITS_ZERO(rds+2, nr-2);
+    }
     else {
         int extra_words;
         long j;

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