Phil Dawes' Stuff - Latest Comments in Searching arrays in X86 assembler with a bloom filter pt 3

Re: Searching arrays in X86 assembler with a bloom filter pt 3

Phil Dawes — Sat, 13 Sep 2008 06:30:13 -0000

Slava Pestov wrote:
> Hi Phil,
>
> I couldn't post a comment on your blog for some reason so I'm posting
> this to the list instead.
>
> The seq>hash word you write already exists in the sets vocabulary, its
> called unique.
>
> And (prepare-filter) looks nicer if you use fry:
>
> : (prepare-filter) ( filter seq -- )
> '[ 1048576 mod _ set-bit ] each ;
>
> Slava

Re: Searching arrays in X86 assembler with a bloom filter pt 3

Phil Dawes — Sat, 13 Sep 2008 06:29:11 -0000

@Asm - thanks for the link, that's a handy resource

Re: Searching arrays in X86 assembler with a bloom filter pt 3

Asm — Fri, 12 Sep 2008 19:44:30 -0000

Variable shifts have the count in %cl.

But why bother? bt r,r and bt r,i are only 1 uop on a Core2. Check the instruction timings here: http://www.agner.org/optimize/

Use mov (%eax,%edi,4), %edi and drop the shl $0x2, %edi.

Re: Searching arrays in X86 assembler with a bloom filter pt 3

Anonymous — Fri, 12 Sep 2008 19:15:20 -0000

You can shift by the contents of the CL register, e.g. shl %cl, %eax .