hashinit versus phashinit

[Adrian Chadd]

2008/5/6 Roman Divacky <rdivacky at freebsd.org>:


>  > Most general-purpose hash implementations I've used (e.g., GNU
>  > libstdc++, Sun JDK, Microsoft .NET) use prime table sizes,
>  > probably to make it less likely that programmers will shoot
>  > themselves in the foot with pathological data or bad hash functions.
>
>  yes... a division takes roughly 40 cycles on modern i386 hw, while
>  and is just 1, but does it matter compared to the access times of
>  memory these days?
>
>  the ratio between cpu-speed/mem-speed has changed a lot. I am not
>  arguing if it's still true that avoiding the division helps the performance
>  these days...

My 2c - I'd poke the assembler, a book or two on current
architectures, and combine it with some benchmarking followed by
logical reasoning.

Modern microprocessors don't execute instructions like they used to
before I was born; "divide versus logical shift/operator" speed may be
secondary to pipeline and IU effects, memory access (as mentioned
before), etc.

(I know its not much - but I'm a firm believer in "Science!", and this
is one of those questions which can be understood with a little bit of
it..)




Adrian

-- 
Adrian Chadd - adrian at freebsd.org