From 7a9aeb33dba8d060c60b2bd690172fb7593865d2 Mon Sep 17 00:00:00 2001
From: akr <akr@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>
Date: Sun, 28 Jul 2013 15:14:20 +0000
Subject: [PATCH] * bignum.c (bigdivrem): Specialized implementation added for 
  nx == 2 && ny == 2

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42218 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
---
 ChangeLog |  5 +++++
 bignum.c  | 21 +++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/ChangeLog b/ChangeLog
index 3bc3f680fd..7a011c21c4 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Mon Jul 29 00:11:49 2013  Tanaka Akira  <akr@fsij.org>
+
+	* bignum.c (bigdivrem): Specialized implementation added for
+	  nx == 2 && ny == 2
+
 Sun Jul 28 20:28:41 2013  Masaki Matsushita  <glass.saga@gmail.com>
 
 	* io.c (io_getpartial): use rb_str_locktmp_ensure().
diff --git a/bignum.c b/bignum.c
index 0c6170ab18..1f3f4b4169 100644
--- a/bignum.c
+++ b/bignum.c
@@ -5399,6 +5399,27 @@ bigdivrem(VALUE x, VALUE y, volatile VALUE *divp, volatile VALUE *modp)
 	if (divp) *divp = z;
 	return Qnil;
     }
+    if (nx == 2 && ny == 2) {
+        BDIGIT_DBL x0 = xds[0] | BIGUP(xds[1]);
+        BDIGIT_DBL y0 = yds[0] | BIGUP(yds[1]);
+        BDIGIT_DBL q0 = x0 / y0;
+        BDIGIT_DBL r0 = x0 % y0;
+        if (divp) {
+            z = bignew(bdigit_roomof(sizeof(BDIGIT_DBL)), RBIGNUM_SIGN(x)==RBIGNUM_SIGN(y));
+            zds = BDIGITS(z);
+            zds[0] = BIGLO(q0);
+            zds[1] = BIGLO(BIGDN(q0));
+            *divp = z;
+        }
+        if (modp) {
+            z = bignew(bdigit_roomof(sizeof(BDIGIT_DBL)), RBIGNUM_SIGN(x));
+            zds = BDIGITS(z);
+            zds[0] = BIGLO(r0);
+            zds[1] = BIGLO(BIGDN(r0));
+            *modp = z;
+        }
+        return Qnil;
+    }
 
     if (BDIGIT_MSB(yds[ny-1]) == 0) {
         /* Make yds modifiable. */