As some of you may know, Pharo is being enhanced with support for multiple bytecode sets. This will allow to run at the same time compiled methods with 2 different bytecode sets for experimentation and to add easily the new bytecode set described in this ESUG paper.��

The virtual machine knows which bytecode set the compiled method uses for its encoding based on the sign of its header. This means that on the contrary to right now, a compiled method *can* have a negative header.

The issue is that typically operations such as #bitAnd: or #+ to access bits of the smallinteger does not work the same way on negative integers (2 complement's implementation of integers), resulting in incorrect values. I am fixing the problematic cases in Pharo.��

One case is in Fuel and I can't fix it myself. It's in:

This looks problematic because now header is not a uint anymore but a sint.

In addition, #encodeUint32: uses #bitAnd: which may work differently on negative integers.

What do you fuel experts think ? Is there anything to fix there ?

Best,

Clement