From: Ethan Rublee <no@email>
Date: Mon, 24 Jan 2011 16:59:14 +0000 (+0000)
Subject: revert the hamming distance to use unsigned long, on 64bit machines, using size_t
X-Git-Tag: accepted/tizen/6.0/unified/20201030.111113~7840
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=a47b6c23f5986dced109d0121ebfb2a5c0f1c553;p=platform%2Fupstream%2Fopencv.git

revert the hamming distance to use unsigned long, on 64bit machines, using size_t
with __build_popcountl doesn't return correct number of bits. the ll version should work, but for simplicity,
locking it down to long for now.  TODO add a unit test for the Hamming distance.
---

diff --git a/modules/features2d/src/brief.cpp b/modules/features2d/src/brief.cpp
index f7924de..675b42c 100644
--- a/modules/features2d/src/brief.cpp
+++ b/modules/features2d/src/brief.cpp
@@ -138,13 +138,16 @@ Hamming::ResultType Hamming::operator()(const unsigned char* a, const unsigned c
   }
   else
 #endif  
+  //for portability just use unsigned long -- and use the __builtin_popcountl (see docs for __builtin_popcountl)
+  //as opposed to size_t -- TODO smart switching, if the size_t is a 64bits, use __builtin_popcountll
+  typedef unsigned long pop_t;
   size_t i;
-  const size_t modulo = size % sizeof(size_t);
+  const size_t modulo = size % sizeof(pop_t);
   const size_t end = size - modulo;
-  for (i = 0; i < end; i += sizeof(size_t))
+  for (i = 0; i < end; i += sizeof(pop_t))
   {
-    size_t a2 = *reinterpret_cast<const size_t*> (a + i);
-    size_t b2 = *reinterpret_cast<const size_t*> (b + i);
+    size_t a2 = *reinterpret_cast<const pop_t*> (a + i);
+    size_t b2 = *reinterpret_cast<const pop_t*> (b + i);
     result += __builtin_popcountl(a2 ^ b2);
   }
   if (modulo)