Hi david
I rad the wikipedia page you mention and this looks a bit obvious to me.
I knew this.
now it does not really help fixing the problem you mention.
Stef
Le 11/1/16 10:09, David Allouche a écrit :
Since it's not obvious why xor-ing is a bad way to produce hash, here is a link
that gives some background
https://en.wikipedia.org/wiki/Hash_function#Uniformity
On 11 Jan 2016, at 10:01, David Allouche <[email protected]> wrote:
I happened to look at the new code for LayoutFrame>>#hash
hash
^self species hash bitXor:
(self leftFraction bitXor:
(self leftOffset bitXor:
(self topFraction bitXor:
(self topOffset bitXor:
(self rightFraction bitXor:
(self rightOffset bitXor:
(self bottomFraction bitXor:
self bottomOffset)))))))
This is a terrible, terrible way to compute a hash.
0 xor 0 = 1 xor 1 = 2 xor 2 = etc.
NEVER compute hashes with xor, that's wrong, and it causes horrible, hard to
debug, performance bugs down the road.
SequenceableCollection>>#hash looks more like a correct way of doing it. I do not
know what is the correct, efficient way to reuse this logic in LayoutFrame>>#hash.
By the way, how do you guys do code reviews for code integrated into the core?
