[Bug middle-end/36041] Speed up builtin_popcountll

[jsalavert at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36041

José Salavert Torres <jsalavert at gmail dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |jsalavert at gmail dot com

--- Comment #8 from José Salavert Torres <jsalavert at gmail dot com> 2012-09-05 10:39:45 UTC ---
Hello, there has been any advance in in this issue, Knuth's publication
approach would be great for 8 bit registers also.

Also, allowing different behaviour for each architecture would be better.

In the forums the implementation described here is now like this, seems to use
less operations:

inline unsigned int bitcount32(uint32_t i) {

  //Parallel binary bit add                                                     
  i = i - ((i >> 1) & 0x55555555);
  i = (i & 0x33333333) + ((i >> 2) & 0x33333333);
  return (((i + (i >> 4)) & 0xF0F0F0F) * 0x1010101) >> 24;

}

  //Parallel binary bit add                                                     
  i = i - ((i >> 1) & 0x5555555555555555);                                      
  i = (i & 0x3333333333333333) + ((i >> 2) & 0x3333333333333333);               
  return (((i + (i >> 4)) & 0xF0F0F0F0F0F0F0F) * 0x101010101010101) >> 56;      

}