crossroads

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git clone git://git.finwo.net/app/crossroads
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hash.cc (569B)

      1 #include "mutextable"
      2 
      3 /*
      4  * How to hash a pointer into an unsigned. Based on the famous hashpjw()
      5  * function.
      6  */
      7 
      8 // #define DEBUG
      9 unsigned MutexTable::hash(void *obj) {
     10     unsigned v = 0;
     11     unsigned char *cp = (unsigned char *)obj;
     12     for (size_t i = 0; i < sizeof(obj); i++) {
     13 	v <<= 4;
     14 	v |= *cp++;
     15 	if (unsigned g = v & 0xf0000000) {
     16 	    v = v ^ ( g >> 24 );
     17 	    v = v ^ g;
     18 	}
     19     }
     20     v %= _size;
     21 
     22 #   ifdef DEBUG    
     23     debugmsg("Pointer " << obj << " hashed to bucket " << v <<
     24 	     " (given size " << _size << ")\n");
     25 #   endif
     26     
     27     return v;
     28 }