From 192085bad3471ed7442a147f86a3c85c1958307c Mon Sep 17 00:00:00 2001
From: akr <akr@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>
Date: Sun, 9 Jun 2013 20:39:05 +0000
Subject: [PATCH] * bignum.c (absint_numwords_small): New function.  
 (absint_numwords_generic): Use absint_numwords_small if possible.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41201 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
---
 ChangeLog |  5 +++++
 bignum.c  | 27 +++++++++++++++++++++++++--
 2 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 8f44d71fde..fbce29fce0 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Mon Jun 10 05:38:23 2013  Tanaka Akira  <akr@fsij.org>
+
+	* bignum.c (absint_numwords_small): New function.
+	  (absint_numwords_generic): Use absint_numwords_small if possible.
+
 Mon Jun 10 01:07:57 2013  Tanaka Akira  <akr@fsij.org>
 
 	* bignum.c (absint_numwords_bytes): New function.
diff --git a/bignum.c b/bignum.c
index 3824efadb5..a0a241a066 100644
--- a/bignum.c
+++ b/bignum.c
@@ -555,7 +555,7 @@ absint_numwords_bytes(size_t numbytes, int nlz_bits_in_msbyte, size_t word_numbi
     }
     else {
         s = q - 1;
-        t = word_numbits + r * CHAR_BIT - nlz_bits_in_msbyte;
+        t = word_numbits - nlz_bits_in_msbyte + r * CHAR_BIT;
     }
     div = s + t / word_numbits;
     mod = t % word_numbits;
@@ -565,6 +565,20 @@ absint_numwords_bytes(size_t numbytes, int nlz_bits_in_msbyte, size_t word_numbi
     return numwords;
 }
 
+size_t
+absint_numwords_small(size_t numbytes, int nlz_bits_in_msbyte, size_t word_numbits, size_t *nlz_bits_ret)
+{
+    size_t val_numbits = numbytes * CHAR_BIT - nlz_bits_in_msbyte;
+    size_t div = val_numbits / word_numbits;
+    size_t mod = val_numbits % word_numbits;
+    size_t numwords;
+    size_t nlz_bits;
+    numwords = mod == 0 ? div : div + 1;
+    nlz_bits = mod == 0 ? 0 : word_numbits - mod;
+    *nlz_bits_ret = nlz_bits;
+    return numwords;
+}
+
 size_t
 absint_numwords_generic(size_t numbytes, int nlz_bits_in_msbyte, size_t word_numbits, size_t *nlz_bits_ret)
 {
@@ -634,7 +648,16 @@ rb_absint_numwords(VALUE val, size_t word_numbits, size_t *nlz_bits_ret)
 
     numbytes = rb_absint_size(val, &nlz_bits_in_msbyte);
 
-    if (word_numbits % CHAR_BIT == 0) {
+    if (numbytes <= SIZE_MAX / CHAR_BIT) {
+        numwords = absint_numwords_small(numbytes, nlz_bits_in_msbyte, word_numbits, &nlz_bits);
+#if 0
+        size_t numwords0, nlz_bits0;
+        numwords0 = absint_numwords_generic(numbytes, nlz_bits_in_msbyte, word_numbits, &nlz_bits0);
+        assert(numwords0 == numwords);
+        assert(nlz_bits0 == nlz_bits);
+#endif
+    }
+    else if (word_numbits % CHAR_BIT == 0) {
         numwords = absint_numwords_bytes(numbytes, nlz_bits_in_msbyte, word_numbits, &nlz_bits);
 #if 0
         size_t numwords0, nlz_bits0;