Re: [Gperf-bugs] Gperf 2.7.2 test file questions

[Bruce Lilly]

Bruno Haible wrote:
> Bruce Lilly writes:
>
>
> > Key position set 1,2,6 will always use the first character of the key.
> > For a key of length 5 only positions 1 and 2 of the key are used,
> > compared to 3 positions used for set 2,4,5.
> >
> > Comparing the two key position sets, it should be clear that 2,4,5
> > will be better for keys with length 3 or less, that there is no
> > advantage of either set for keys of length 4 or of length 6 or greater,
> > and that 1,2,6 is more efficient only for keys of length 5.
>
>
> On the other hand - if all positions can be chosen small enough (<=
> minimal keyword length), then there is no switch statement in the
> generated code, and this makes the code faster in all cases. So this
> is an argument for trying to choose the positions as small as
> possible.

Though I haven't looked at it recently, I think the code I submitted
makes a final pass through the tentatively selected keys to see if
any are redundant and can be eliminated.

Beware generalizing: the keyword set

a
bcdefgh

can use position 1. However, note that position 7 can alternatively
be used as the sole key position, and will be more efficient than
using position 1 for key lengths of 6 or less, as no characters from
the key need be used.  Lack of a switch statement does not necessarily
mean faster code.

Best regards,
   Bruce Lilly