Hi Phillipe,

On Mon, May 26, 2014 at 12:51 AM, Philippe Marschall <philippe.marschall@netcetera.ch> wrote:

Hi

I have been investigating why Dictionary look up performance with String keys is not as good as I would expected. Something I noted is that String >> #= is implemented in terms of #compare:with:collated:. There is no short circuit if Strings are not the same size. In my case some Strings have the same prefix but a different length eg 'Content-Type' and 'Content-Length'. In that case a #compare:with:collated: is performed even though we know in advance the answer will be false because they have different sizes.

Why not rewrite

String>>= aString

"Answer whether the receiver sorts equally as aString.

The collation order is simple ascii (with case differences)."

aString isString ifFalse: [ ^ false ].

^ (self compare: self with: aString collated: AsciiOrder) = 2

String>>= aString

"Answer whether the receiver sorts equally as aString.

The collation order is simple ascii (with case differences)."

(aString isString

and: [self size = aString size]) ifFalse: [^false].

^ (self compare: self withSize: with: aString collated: AsciiOrder) = 2

One /could/ add a replacement compare:with:collated: primitive primitiveCompareString which took the sizes as arguments to avoid asking twice. But it wouldn't be safe. One could abuse the primitive and lie about the size. So I suspect it is best to add the size check to String>>#= and accept the duplication of the primitive finding the sizes of the two strings. The cost in the primitive is minimal. A WideString version of the primitive might pay its way, but if Spur and Sista arrive soon the primitive shouldn't be faster than the optimised Smalltalk code.
--
best,

Eliot