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Changes to const void* hash function as suggested by Jan in

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http://www.wildfiregames.com/forum/index.php?showtopic=9642&pid=167148&st=20&#entry167148

This was SVN commit r3532.
This commit is contained in:
prefect 2006-02-18 23:21:05 +00:00
parent a82888286f
commit 71dab351bd
1 changed files with 12 additions and 9 deletions
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21
source/lib/sysdep/sysdep.h
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@ -292,19 +292,22 @@ namespace __gnu_cxx
template<> struct hash<const void*>
{
// TODO: Is this a good hash function for pointers?
// The basic idea is to avoid patterns that are caused by alignment of structures
// in memory and of heap allocations
// Nemesi hash function (see: http://mail-index.netbsd.org/tech-kern/2001/11/30/0001.html)
// treating the pointer as an array of bytes that is hashed.
size_t operator()(const void* __x) const
{
size_t val = (size_t)__x;
const unsigned char* data = (unsigned char*)&val;
size_t h = 0;
union {
const void* ptr;
unsigned char bytes[sizeof(void*)];
} val;
size_t h = 5381;
for(uint i = 0; i < sizeof(val); ++i, ++data)
h = 257*h + *data;
val.ptr = __x;
return h;
for(uint i = 0; i < sizeof(val); ++i)
h = 257*h + val.bytes[i];
return 257*h;
}
};
}