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SSE4 instructions
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Vincent Diepeveen



Joined: 09 Mar 2006
Posts: 1738
Location: The Netherlands
PostPost subject: Re: SSE4 instructions    Posted: Thu May 24, 2012 12:35 pm Reply to topic Reply with quote
mar wrote:
Engin wrote:

MY_INLINE int my_pop_cnt64 (const uint64_t a)
{
if(a) return (count_word[0xffff & a] +
count_word[0xffff & (a >> 16)] +
count_word[0xffff & (a >> 32)] +
count_word[0xffff & (a >> 48)] ) ;

return (0);
}


Hi Engin,

yes i also use a LUT in cheng. Also 64K table, 4 lookups.


You also do the useless 'if( a )' clause in front of it?
Without it it's 2 cycles provided your results are in L1d, otherwise you have to get it out of L2 or L3 which is slow.

Quote:

Doing 8 256-byte lookups proved slower, and any other fancy formulas proved much slower (note i only tested in 32-bit mode).

it's 4 cycles yet lots of problems for L1d to keep up with the result,
also i see the above code uses a '+' (PLUS). You can also use | (OR) of course, which is faster on paper, except L1d problems again.

Quote:

I'm not sure but i believe only SSE4 popcnt was faster.


Of course it is faster if other instructions already are in SIMD. The SSE4 can do 2 at a time which always is faster. AVX can do 4 at a time which is even faster.

So if you write simple test, usually compiler will fool everyone there.

Quote:

However even with popcnt the speedup was really negligible so i never enabled it and i believe it's useless. At my level (~2500 elo engine +- rating list elo normalization offset) certainly.
One more binary for how much? 1, 2, 5 or 10 elo at best perhaps? Not worth it IMO unless want to make some nerds happy Wink


No elo at all of course, except if you mess up.
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Display posts from previous:   
Subject Author Date/Time
SSE4 instructions Maurizio Maglio Mon May 21, 2012 8:48 pm
      Re: SSE4 instructions Adam Hair Mon May 21, 2012 10:47 pm
            Re: SSE4 instructions Maurizio Maglio Tue May 22, 2012 7:47 am
      Re: SSE4 instructions Joona Kiiski Tue May 22, 2012 1:55 pm
            Re: SSE4 instructions Engin Üstün Tue May 22, 2012 8:11 pm
                  Re: SSE4 instructions Maurizio Maglio Tue May 22, 2012 8:41 pm
                  Re: SSE4 instructions Robert Hyatt Wed May 23, 2012 3:39 pm
      Re: SSE4 instructions Engin Üstün Tue May 22, 2012 7:31 pm
            Re: SSE4 instructions Engin Üstün Tue May 22, 2012 7:34 pm
                  Re: SSE4 instructions Ricardo Barreira Wed May 23, 2012 7:40 am
                        Re: SSE4 instructions Robert Hyatt Wed May 23, 2012 3:37 pm
                              Re: SSE4 instructions Richard Vida Wed May 23, 2012 5:28 pm
                                    Re: SSE4 instructions Robert Hyatt Wed May 23, 2012 5:47 pm
                                          Re: SSE4 instructions Ricardo Barreira Sat May 26, 2012 3:14 pm
                                    Re: SSE4 instructions Engin Üstün Wed May 23, 2012 10:02 pm
                                          Re: SSE4 instructions Vincent Diepeveen Thu May 24, 2012 12:02 am
                                                Re: SSE4 instructions Engin Üstün Thu May 24, 2012 3:54 pm
                                                      Re: SSE4 instructions Engin Üstün Thu May 24, 2012 4:07 pm
                                          Re: SSE4 instructions Lucas Braesch Thu May 24, 2012 11:03 am
                                          Re: SSE4 instructions Martin Sedlak Thu May 24, 2012 11:47 am
                                                Re: SSE4 instructions Vincent Diepeveen Thu May 24, 2012 12:35 pm
                                                      Re: SSE4 instructions Martin Sedlak Thu May 24, 2012 12:46 pm
                                                      Re: SSE4 instructions Engin Üstün Thu May 24, 2012 4:24 pm
                                    Re: SSE4 instructions Engin Üstün Thu May 24, 2012 4:41 pm
                        Re: SSE4 instructions Engin Üstün Wed May 23, 2012 4:35 pm
                              Re: SSE4 instructions Robert Hyatt Wed May 23, 2012 5:48 pm
                                    Re: SSE4 instructions Engin Üstün Wed May 23, 2012 10:28 pm
                                          Re: SSE4 instructions Robert Hyatt Thu May 24, 2012 3:41 pm
                                                Re: SSE4 instructions Engin Üstün Thu May 24, 2012 4:31 pm
                        Re: SSE4 instructions Engin Üstün Thu May 24, 2012 4:35 pm
      Re: SSE4 instructions Don Dailey Thu May 24, 2012 9:09 pm
            Re: SSE4 instructions Richard Vida Thu May 24, 2012 9:21 pm
                  Re: SSE4 instructions Vincent Diepeveen Fri May 25, 2012 12:19 am
                  Re: SSE4 instructions Engin Üstün Fri May 25, 2012 10:44 pm
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