From 0784d6540f3cc8d2719e47a06e9c71ad44d91884 Mon Sep 17 00:00:00 2001
From: rakshasa <sundell.software@gmail.com>
Date: Sun, 2 Oct 2011 15:57:22 +0000
Subject: [PATCH] * Switched to using '__builtin_popcount' for counting bits in
 bitfield.

git-svn-id: svn://rakshasa.no/libtorrent/trunk/rtorrent@1292 e378c898-3ddf-0310-93e7-cc216c733640
---
 rak/algorithm.h   | 20 ++++++++++++++++++++
 scripts/common.m4 | 15 +++++++++++++++
 2 files changed, 35 insertions(+)

diff --git a/rak/algorithm.h b/rak/algorithm.h
index 3dfa9f36..5f4f022c 100644
--- a/rak/algorithm.h
+++ b/rak/algorithm.h
@@ -155,6 +155,26 @@ make_base(_InputIter __first, _InputIter __last, _Ftor __ftor) {
   return __base;
 }
 
+template<typename T>
+inline int popcount_wrapper(T t) {
+#if USE_BUILTIN_POPCOUNT
+  if (std::numeric_limits<T>::digits <= std::numeric_limits<unsigned int>::digits)
+    return __builtin_popcount(t);
+  else
+    return __builtin_popcountll(t);
+#else
+#error __builtin_popcount not found.
+  unsigned int count = 0;
+  
+  while (t) {
+    count += t & 0x1;
+    t >> 1;
+  }
+
+  return count;
+#endif
+}
+
 }
 
 #endif
diff --git a/scripts/common.m4 b/scripts/common.m4
index 197bf997..dc482c59 100644
--- a/scripts/common.m4
+++ b/scripts/common.m4
@@ -181,6 +181,21 @@ AC_DEFUN([TORRENT_CHECK_MADVISE], [
   ])
 ])
 
+AC_DEFUN([TORRENT_CHECK_POPCOUNT], [
+  AC_MSG_CHECKING(for __builtin_popcount)
+
+  AC_COMPILE_IFELSE(
+    [[
+      void f() { __builtin_popcount(0); }
+    ]],
+    [
+      AC_MSG_RESULT(yes)
+      AC_DEFINE(USE_BUILTIN_POPCOUNT, 1, Use __builtin_popcount.)
+    ], [
+      AC_MSG_RESULT(no)
+  ])
+])
+
 AC_DEFUN([TORRENT_CHECK_CACHELINE], [
   AC_MSG_CHECKING(for cacheline)