[Vm-dev] Sign-bit bug in character literals > 16r7FFF ... related to SistaV1?

Marcel Taeumel marcel.taeumel at hpi.de
Tue Mar 8 16:57:32 UTC 2022

Hi Eliot, hi all --

I think we have an sign-bit bug for character literals with code points > 16r7FFF.

Steps to reproduce:

1. Print it: "Character value: 16r8000"
2. Inspect the result by evaluating the character literal or send #asInteger to it. It will most likely not render in a standard Squeak and show up like "$? asInteger".

In a 32-bit VM, I will get the (positive) integer value 16r3FFF8000.
In a 64-bit VM, I will get the (negative) integer value '-16r8000'.

Somehow, starting at bit 0, the bits 16 to 29 flip from 0 to 1. In 64-bit, this means a negative number. Not sure about bits 30 and 31 here.

Is there a bug in the upper tag bits of immediate characters?
Is this related to the 2-byte or 3-byte byte codes in SistaV1?

Works fine up to 16r7FFF. (This is unrelated to #leadingChar. Mine was 0 in this experiment.)

VM: 202112201228 (VMMaker.oscog-eem.3116)

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