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undocumented method is quest of comment

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Stephane Ducasse-3

undocumented method is quest of comment

Hi guys

I would love to have a better method comment for

hashMultiply
| low |
low := self bitAnd: 16383.
^(16r260D * low + ((16r260D * (self bitShift: -14) + (16r0065 *
low) bitAnd: 16383) * 16384))
bitAnd: 16r0FFFFFFF

Some love?

Stef

Nicolas Cellier

Re: undocumented method is quest of comment

It's not documented because hashing is complex...

The goal is to shuffle the receiver bits and distribute them over the available 28bits used for hash codes.

why and how it does so is a tough subject, Andres Valloud wrote a whole book on it ;)

The basic operation which is emulated is relatively simple, but implementation is overly complex, because it tries to avoid creating LargeIntegers in 32bits VM

*16384 is <=> bitShift: 14

bitAnd 16383 is <=> isolating lowest 14 bits...

While at it, one should also rewrite the method contents in order to use the new primitive available

and profit by more efficient 64bit version for 64bit VM...

Fortunately, one can still pick the methods from Squeak :)

then forget the original authors because it really does not matter, does it?

2017-11-16 22:25 GMT+01:00 Stephane Ducasse <[hidden email]>:

Hi guys

I would love to have a better method comment for

hashMultiply
| low |
low := self bitAnd: 16383.
^(16r260D * low + ((16r260D * (self bitShift: -14) + (16r0065 *
low) bitAnd: 16383) * 16384))
bitAnd: 16r0FFFFFFF

Some love?

Stef

hashMultiply.st (1K) Download Attachment

Pavel Krivanek-3

Re: undocumented method is quest of comment

https://github.com/pharo-project/pharo/pull/487

2017-11-16 23:32 GMT+01:00 Nicolas Cellier <[hidden email]>:

It's not documented because hashing is complex...
The goal is to shuffle the receiver bits and distribute them over the available 28bits used for hash codes.
why and how it does so is a tough subject, Andres Valloud wrote a whole book on it ;)

The basic operation which is emulated is relatively simple, but implementation is overly complex, because it tries to avoid creating LargeIntegers in 32bits VM

*16384 is <=> bitShift: 14
bitAnd 16383 is <=> isolating lowest 14 bits...

While at it, one should also rewrite the method contents in order to use the new primitive available
and profit by more efficient 64bit version for 64bit VM...

Fortunately, one can still pick the methods from Squeak :)
then forget the original authors because it really does not matter, does it?

2017-11-16 22:25 GMT+01:00 Stephane Ducasse <[hidden email]>:
Hi guys

I would love to have a better method comment for

hashMultiply
| low |
low := self bitAnd: 16383.
^(16r260D * low + ((16r260D * (self bitShift: -14) + (16r0065 *
low) bitAnd: 16383) * 16384))
bitAnd: 16r0FFFFFFF

Some love?

Stef

Nicolas Cellier

Re: undocumented method is quest of comment

One little action is worth a thousand words :)

2017-11-17 11:51 GMT+01:00 Pavel Krivanek <[hidden email]>:

https://github.com/pharo-project/pharo/pull/487

2017-11-16 23:32 GMT+01:00 Nicolas Cellier <[hidden email]>:
It's not documented because hashing is complex...
The goal is to shuffle the receiver bits and distribute them over the available 28bits used for hash codes.
why and how it does so is a tough subject, Andres Valloud wrote a whole book on it ;)

The basic operation which is emulated is relatively simple, but implementation is overly complex, because it tries to avoid creating LargeIntegers in 32bits VM

*16384 is <=> bitShift: 14
bitAnd 16383 is <=> isolating lowest 14 bits...

While at it, one should also rewrite the method contents in order to use the new primitive available
and profit by more efficient 64bit version for 64bit VM...

Fortunately, one can still pick the methods from Squeak :)
then forget the original authors because it really does not matter, does it?

2017-11-16 22:25 GMT+01:00 Stephane Ducasse <[hidden email]>:
Hi guys

I would love to have a better method comment for

hashMultiply
| low |
low := self bitAnd: 16383.
^(16r260D * low + ((16r260D * (self bitShift: -14) + (16r0065 *
low) bitAnd: 16383) * 16384))
bitAnd: 16r0FFFFFFF

Some love?

Stef

Stephane Ducasse-3

Re: undocumented method is quest of comment

Indeed no little action is worth a thousand words.
Everybody plants its own seed.

Tx nicolas and Pavel.
Stef

On Fri, Nov 17, 2017 at 3:00 PM, Nicolas Cellier
<[hidden email]> wrote:

> One little action is worth a thousand words :)
>
>
> 2017-11-17 11:51 GMT+01:00 Pavel Krivanek <[hidden email]>:
>>
>> https://github.com/pharo-project/pharo/pull/487
>>
>> 2017-11-16 23:32 GMT+01:00 Nicolas Cellier
>> <[hidden email]>:
>>>
>>> It's not documented because hashing is complex...
>>> The goal is to shuffle the receiver bits and distribute them over the
>>> available 28bits used for hash codes.
>>> why and how it does so is a tough subject, Andres Valloud wrote a whole
>>> book on it ;)
>>>
>>> The basic operation which is emulated is relatively simple, but
>>> implementation is overly complex, because it tries to avoid creating
>>> LargeIntegers in 32bits VM
>>>
>>> *16384 is <=> bitShift: 14
>>> bitAnd 16383 is <=> isolating lowest 14 bits...
>>>
>>> While at it, one should also rewrite the method contents in order to use
>>> the new primitive available
>>> and profit by more efficient 64bit version for 64bit VM...
>>>
>>> Fortunately, one can still pick the methods from Squeak :)
>>> then forget the original authors because it really does not matter, does
>>> it?
>>>
>>>
>>> 2017-11-16 22:25 GMT+01:00 Stephane Ducasse <[hidden email]>:
>>>>
>>>> Hi guys
>>>>
>>>> I would love to have a better method comment for
>>>>
>>>>
>>>> hashMultiply
>>>> | low |
>>>> low := self bitAnd: 16383.
>>>> ^(16r260D * low + ((16r260D * (self bitShift: -14) + (16r0065 *
>>>> low) bitAnd: 16383) * 16384))
>>>> bitAnd: 16r0FFFFFFF
>>>>
>>>>
>>>> Some love?
>>>>
>>>> Stef
>>>>
>>>
>>
>