Re: levenshtein_less_equal (was: multibyte charater set in levenshtein function)

On Wed, Oct 13, 2010 at 11:42 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> On Wed, Oct 13, 2010 at 10:51 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>> But the main point is that 6% performance penalty in a non-core function
>>> is well below my threshold of pain.
>
>> Well, then you have to wonder whether it's worth having the
>> lesss-than-or-equal-to version around at all.  That's only about 2x
>> faster on the same test case.
>
> "Same" test case?  I thought they did different things?

levenshtein_less_equal(a, b, max_d) returns the same value as
levenshtein(a, b) if levenshtein(a, b) <= max_d. Otherwise it returns
max_d + 1. So it's the same test case with a small distance bound (2)
applied. As Alexander says, the value of levenshtein_less_equal
accelerates pretty rapidly when long strings are involved, so it seems
worth having, but I'm not sure I agree that the slowdown to the basic
function is negligible. It is not really all that much #ifdef hackery
to avoid it.

--
Robert Haas
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