[Pharo-project] Hash values
Hi! Apparently in Pharo 1.1, hash values may be greater than 4096. What is the range of the hash values? Cheers, Alexandre
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 Pharo-project@lists.gforge.inria.fr 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 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
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 ^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;.
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 Pharo-project@lists.gforge.inria.fr 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 Pharo-project@lists.gforge.inria.fr http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
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 Pharo-project@lists.gforge.inria.fr 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. Cheers, Henry
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 Pharo-project@lists.gforge.inria.fr 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
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 Pharo-project@lists.gforge.inria.fr 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 Pharo-project@lists.gforge.inria.fr http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
participants (7)
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Alexandre Bergel -
Alexandre Bergel -
Andres Valloud -
Henrik Johansen -
Henrik Sperre Johansen
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Levente Uzonyi -
Stéphane Ducasse