initial working frustum culling implementation

[chaz/yoink] / src / Moof / Hash.cc

diff --git a/src/Moof/Hash.cc b/src/Moof/Hash.cc
new file mode 100644 (file)
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--- /dev/null
+++ b/src/Moof/Hash.cc
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+
+/*******************************************************************************
+
+ Copyright (c) 2009, Charles McGarvey
+ All rights reserved.
+ 
+ Redistribution   and   use  in  source  and  binary  forms,  with  or  without
+ modification, are permitted provided that the following conditions are met:
+ 
+   * Redistributions  of  source  code  must retain the above copyright notice,
+     this list of conditions and the following disclaimer.
+   * Redistributions  in binary form must reproduce the above copyright notice,
+     this  list of conditions and the following disclaimer in the documentation
+     and/or other materials provided with the distribution.
+ 
+ THIS  SOFTWARE  IS  PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ AND  ANY  EXPRESS  OR  IMPLIED  WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ DISCLAIMED.  IN  NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ FOR  ANY  DIRECT,  INDIRECT,  INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ DAMAGES  (INCLUDING,  BUT  NOT  LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ SERVICES;  LOSS  OF  USE,  DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ CAUSED  AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ OR  TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+*******************************************************************************/
+
+#include "Hash.hh"
+
+
+namespace Mf {
+
+
+//-----------------------------------------------------------------------------
+// MurmurHash2, by Austin Appleby
+
+// Note - This code makes a few assumptions about how your machine behaves -
+
+// 1. We can read a 4-byte value from any address without crashing
+// 2. sizeof(int) == 4
+
+// And it has a few limitations -
+
+// 1. It will not work incrementally.
+// 2. It will not produce the same results on little-endian and big-endian
+//    machines.
+
+unsigned int MurmurHash2_(const void* key, int len, unsigned int seed)
+{
+       // 'm' and 'r' are mixing constants generated offline.
+       // They're not really 'magic', they just happen to work well.
+
+       const unsigned int m = 0x5bd1e995;
+       const int r = 24;
+
+       // Initialize the hash to a 'random' value
+
+       unsigned int h = seed ^ len;
+
+       // Mix 4 bytes at a time into the hash
+
+       const unsigned char* data = (const unsigned char*)key;
+
+       while (len >= 4)
+       {
+               unsigned int k = *(unsigned int*)data;
+
+               k *= m; 
+               k ^= k >> r; 
+               k *= m; 
+               
+               h *= m; 
+               h ^= k;
+
+               data += 4;
+               len -= 4;
+       }
+       
+       // Handle the last few bytes of the input array
+
+       switch (len)
+       {
+       case 3: h ^= data[2] << 16;
+       case 2: h ^= data[1] << 8;
+       case 1: h ^= data[0];
+               h *= m;
+       };
+
+       // Do a few final mixes of the hash to ensure the last few
+       // bytes are well-incorporated.
+
+       h ^= h >> 13;
+       h *= m;
+       h ^= h >> 15;
+
+       return h;
+} 
+
+
+} // namespace Mf
+
+/** vim: set ts=4 sw=4 tw=80: *************************************************/
+