On Wed, Nov 2, 2011 at 1:15 PM, Igor Stasenko siguctua@gmail.com wrote:
On 2 November 2011 20:55, Eliot Miranda eliot.miranda@gmail.com wrote:
On Wed, Nov 2, 2011 at 11:33 AM, Levente Uzonyi leves@elte.hu wrote:
On Wed, 2 Nov 2011, Igor Stasenko wrote:
Here the original implementation, which Array inherits from SequenceableCollection:
at: index ifAbsent: exceptionBlock "Answer the element at my position index. If I do not contain
an element
at index, answer the result of evaluating the argument,exceptionBlock."
(index between: 1 and: self size) ifTrue: [^ self at: index]. ^ exceptionBlock valuethe thing is, that #at: primivite also doing a range checking and fails if index is invalid, so if index is valid, as result we performing a range checking twice instead of just once.
Here the simple implementation how to make things faster: fat: index "Primitive. Assumes receiver is indexable. Answer the value of
an
indexable element in the receiver. Fail if the argument indexis not an
Integer or is out of bounds. Essential. See Object documentation whatIsAPrimitive. Read the class comment for a discussion aboutthat the fact
that the index can be a float." <primitive: 60> ^ #ploppfat: index ifAbsent: aBlock | x | x := (self fat: index). x == #plopp ifTrue: [ ^ aBlock value ]. ^ x
And speedup is almost 2 times:
[ 1000000 timesRepeat: [ #(1 2 4 5 56 67 67) at: 1 ifAbsent: nil ] ]
timeToRun
39
[ 1000000 timesRepeat: [ #(1 2 4 5 56 67 67) at: 1 ifAbsent: nil ] ]
timeToRun
20
Even when index is out of range, it is still much faster:
[ 1000000 timesRepeat: [ #(1 2 4 5 56 67 67) at: 100 ifAbsent: nil ] ]
timeToRun
35
[ 1000000 timesRepeat: [ #(1 2 4 5 56 67 67) fat: 100 ifAbsent: nil ] ] timeToRun
24
The problem, of course, that trick with #plopp is a dirty hack. Because if array include an #plopp object as element, it will report as it absent, instead of answering it. There is no way to ensure that any arbitrary object are never included as element in array, so this is no-go for generic replacement. But in controlled environment, when you know that none of arrays which you using with #fat:ifAbsent: will ever include #plopp (or pick your own unique object) it may be a good alternative.
I've been thinking about this earlier and there's a much nicer and
simpler solution, though it requires vm changes :). The idea is to change primitive 60 to work for 2 parameters too, so #at:ifAbsent: could also use the primitive directly. There were a few changes about #at: recently (mirror prims, cog), so I'm not sure it's still easy to change the primitive.
his is neat, but it wouldn't be an extension to primitive 60 but a new
primitive that would ignore its top of stack. primitive 60 can operate with 2 args,when used as a mirror primitive, but then it ignores the receiver. Your usage would ignore the last argument.
So choose a primitive number and I'll make it so...
Of course i was thinking about changing VM too. But i am uncertain if it worth doing so, because maybe this is too low reward for putting effort in it.
But if we going to make new prim , here's what i'd like to have
- use proper prim error code(s) to distinguish between cases:
- a receiver is not indexable/variable object
- an index is integer, but points outside of array's range
- an object passed as index is non-integer
I agree. I was going to brag that the Cog VM already has this implemented but the error code returned for a non-indexable receiver is wrong. It should be #'bad receiver' but the prim always answers #'bad index'. I'll fix this. Primitive error codes and relevant usage in primitives still need to be ported to the standard VM though.
this is to eliminate code which tries to guess what is really happen:
<primitive: 60> index isInteger ifTrue: [self class isVariable ifTrue: [self errorSubscriptBounds: index] ifFalse: [self errorNotIndexable]]. index isNumber ifTrue: [^self at: index asInteger] ifFalse: [self errorNonIntegerIndex]
Btw, this is an example of how much more flexibility we could earn, if we could rewrite basic prims to count (and use) arguments from bottom of stack (receiver) instead from top, so primitives could be used in more flexible manner.
-- Best regards, Igor Stasenko.