Hash values
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Hi!
Apparently in Pharo 1.1, hash values may be greater than 4096. What is the range of the hash values? Cheers, Alexandre _______________________________________________ Pharo-project mailing list [hidden email] http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project |
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On 02.06.2010 00:15, Alexandre Bergel wrote:
> Hi! > > Apparently in Pharo 1.1, hash values may be greater than 4096. What is the range of the hash values? > > Cheers, > Alexandre > > _______________________________________________ > Pharo-project mailing list > [hidden email] > http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project Identity hashes can't, but they are scaled in 1.1, to avoid bad clustering for objects not redefining hash. Basically they're multiplied by 2^18, which gives the largest possible range while still keeping all small integers. See ProtoObject>>identityHash for details, old identityHash is now basicIdentityHash. Cheers, Henry _______________________________________________ Pharo-project mailing list [hidden email] http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project |
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>>
> Hash values could always be greater than 4096 :) > Identity hashes can't, but they are scaled in 1.1, to avoid bad clustering for objects not redefining hash. > Basically they're multiplied by 2^18, which gives the largest possible range while still keeping all small integers. > See ProtoObject>>identityHash for details, old identityHash is now basicIdentityHash. > Cheers, Thanks for the update Henry! Cheers, Alexandre -- _,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;: Alexandre Bergel http://www.bergel.eu ^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;. _______________________________________________ Pharo-project mailing list [hidden email] http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project |
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In reply to this post by Henrik Sperre Johansen
On Wed, 2 Jun 2010, Henrik Sperre Johansen wrote:
> On 02.06.2010 00:15, Alexandre Bergel wrote: >> Hi! >> >> Apparently in Pharo 1.1, hash values may be greater than 4096. What is the >> range of the hash values? >> >> Cheers, >> Alexandre >> >> _______________________________________________ >> Pharo-project mailing list >> [hidden email] >> http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project > Hash values could always be greater than 4096 :) > Identity hashes can't, but they are scaled in 1.1, to avoid bad clustering That's not true. You may be surprised, but the value of #identityHash can be any SmallInteger. Just try this: {SmallInteger minVal. SmallInteger maxVal} collect: #identityHash. > for objects not redefining hash. > Basically they're multiplied by 2^18, which gives the largest possible range > while still keeping all small integers. > See ProtoObject>>identityHash for details, old identityHash is now > basicIdentityHash. This may cause compatibility problems for packages which implement custom hashes or custom hashed collections. I think Magma will be affected by this, though I didn't check the code. Levente > Cheers, > Henry > > _______________________________________________ > Pharo-project mailing list > [hidden email] > http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project > _______________________________________________ Pharo-project mailing list [hidden email] http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project |
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On Jun 2, 2010, at 3:04 32AM, Levente Uzonyi wrote: > On Wed, 2 Jun 2010, Henrik Sperre Johansen wrote: > >> On 02.06.2010 00:15, Alexandre Bergel wrote: >>> Hi! >>> Apparently in Pharo 1.1, hash values may be greater than 4096. What is the range of the hash values? >>> Cheers, >>> Alexandre >>> _______________________________________________ >>> Pharo-project mailing list >>> [hidden email] >>> http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project >> Hash values could always be greater than 4096 :) >> Identity hashes can't, but they are scaled in 1.1, to avoid bad clustering > > That's not true. You may be surprised, but the value of #identityHash can be any SmallInteger. Just try this: > {SmallInteger minVal. SmallInteger maxVal} collect: #identityHash. > >> for objects not redefining hash. >> Basically they're multiplied by 2^18, which gives the largest possible range while still keeping all small integers. >> See ProtoObject>>identityHash for details, old identityHash is now basicIdentityHash. > > This may cause compatibility problems for packages which implement custom hashes or custom hashed collections. I think Magma will be affected by this, though I didn't check the code. > > Not sure why it ended up basicIdentity / identity instead of identity / scaledIdentity, but that's true. Cheers, Henry _______________________________________________ Pharo-project mailing list [hidden email] http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project |
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>>>
>>>> Hi! >>>> Apparently in Pharo 1.1, hash values may be greater than 4096. What is the range of the hash values? >>>> Cheers, >>>> Alexandre >>>> _______________________________________________ >>>> Pharo-project mailing list >>>> [hidden email] >>>> http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project >>> Hash values could always be greater than 4096 :) >>> Identity hashes can't, but they are scaled in 1.1, to avoid bad clustering >> >> That's not true. You may be surprised, but the value of #identityHash can be any SmallInteger. Just try this: >> {SmallInteger minVal. SmallInteger maxVal} collect: #identityHash. > Yeah, forgot about that one. >> >>> for objects not redefining hash. >>> Basically they're multiplied by 2^18, which gives the largest possible range while still keeping all small integers. >>> See ProtoObject>>identityHash for details, old identityHash is now basicIdentityHash. >> >> This may cause compatibility problems for packages which implement custom hashes or custom hashed collections. I think Magma will be affected by this, though I didn't check the code. >> >> > Not sure why it ended up basicIdentity / identity instead of identity / scaledIdentity, but that's true. so what should we do in 1.2? Stef _______________________________________________ Pharo-project mailing list [hidden email] http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project |
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I still think leaving identityHash alone and using scaledIdentityHash to
multiply by 2^18 is better for backwards compatibility. However, I do not know how much of a problem changing identityHash will cause for existing code. Something that has always bugged me about changing identityHash is that (as far as I've seen) identityHash is typically assumed to answer whatever bits are in the object header. I am not sure introducing an exception in Pharo, or even changing the assumption that has held for decades, is worth the benefit of changing identityHash. On 6/2/10 0:44 , Stéphane Ducasse wrote: >>>> >>>>> Hi! >>>>> Apparently in Pharo 1.1, hash values may be greater than 4096. What is the range of the hash values? >>>>> Cheers, >>>>> Alexandre >>>>> _______________________________________________ >>>>> Pharo-project mailing list >>>>> [hidden email] >>>>> http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project >>>>> >>>> Hash values could always be greater than 4096 :) >>>> Identity hashes can't, but they are scaled in 1.1, to avoid bad clustering >>>> >>> That's not true. You may be surprised, but the value of #identityHash can be any SmallInteger. Just try this: >>> {SmallInteger minVal. SmallInteger maxVal} collect: #identityHash. >>> >> Yeah, forgot about that one. >> >>> >>>> for objects not redefining hash. >>>> Basically they're multiplied by 2^18, which gives the largest possible range while still keeping all small integers. >>>> See ProtoObject>>identityHash for details, old identityHash is now basicIdentityHash. >>>> >>> This may cause compatibility problems for packages which implement custom hashes or custom hashed collections. I think Magma will be affected by this, though I didn't check the code. >>> >>> >>> >> Not sure why it ended up basicIdentity / identity instead of identity / scaledIdentity, but that's true. >> > so what should we do in 1.2? > > Stef > _______________________________________________ > Pharo-project mailing list > [hidden email] > http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project > > _______________________________________________ Pharo-project mailing list [hidden email] http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project |
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