[squeak-dev] 32 vs 64 bits and large integer hash

Eliot Miranda eliot.miranda at gmail.com
Wed Nov 21 18:45:54 UTC 2018

Hi All,

    right now we have the following definition of

^ByteArray hashBytes: self startingWith: self species hash

which means that for all integers outside of the 32-bit SmallInteger range
(-2 ^ 30 to 2 ^ 30 - 1), the 32-bit system and the 64-bit system answer
different values for hash.

e.g. in 64 bits: (2 raisedTo: 30) hash 1073741824
 but in 32 bits: (2 raisedTo: 30) hash 230045764

This is unsatisfactory.  I propose changing Large(Positive)Integer>>hash to

^self digitLength <= 8
ifTrue: [self]
ifFalse: [ByteArray hashBytes: self startingWith: self species hash]

P.S. Note that this will not break Float hash, which is defined as

"Hash is reimplemented because = is implemented. Both words of the float
are used. (The bitShift:'s ensure that the intermediate results do not
become a large integer.) Care is taken to answer same hash as an equal

(self isFinite and: [self fractionPart = 0.0]) ifTrue: [^self truncated
^ ((self basicAt: 1) bitShift: -4) +
  ((self basicAt: 2) bitShift: -4)

P.P.S. I *think* that "(self isFinite and: [self fractionPart = 0.0])" is
equivalent to "self - self = self fractionPart" ;-)

best, Eliot
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.squeakfoundation.org/pipermail/squeak-dev/attachments/20181121/7ae0f1b3/attachment.html>

More information about the Squeak-dev mailing list