[Vm-dev] Spur 64-bits. Ugh, this could be a slog...

Eliot Miranda eliot.miranda at gmail.com
Wed Nov 19 03:12:12 UTC 2014

Hi All,

    I'm making good progress on 64-bit Spur in the Stack VM simulator.  But
I've just noticed an image-level issue which could be indicative of lots of
32-bit assumptions baked into the Squeal/Pharo/Newspeak systems.

SmallInteger>>digitAt: n
"Answer the value of an indexable field in the receiver.
LargePositiveInteger uses bytes of base two number, and each is a 'digit'
base 256.  Fail if the argument (the index) is not an Integer or is out of
n>4 ifTrue: [^ 0].
self < 0
[self = SmallInteger minVal ifTrue:
["Can't negate minVal -- treat specially"
^ #(0 0 0 64) at: n].
^ ((0-self) bitShift: (1-n)*8) bitAnd: 16rFF]
ifFalse: [^ (self bitShift: (1-n)*8) bitAnd: 16rFF]

This assumes that SmallInteger is only ever 4 bytes, which is unacceptably
wasteful for my approach to 64-bits. In 64-bit Spur, SmallIntegers are
61-bit 2's complement.

I'm raising this example at this point to see if the community might find
similar issues and bring them to my attention.
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