On 10 June 2016 at 20:17, Eliot Miranda <eliot.miranda@gmail.com> wrote:

Hi Ben,

this time I'll try and answer your question rather than my brain fart...

> On Jun 9, 2016, at 6:46 PM, Ben Coman <btc@openinworld.com> wrote:
>
>
> Just curious about the difference in instructionPointer between these two...
>
> StackInterpreter>>transferTo:
> self assertValidExecutionPointe: instructionPointer + 1 r:
> framePointer s: stackPointer.
>
>
> CoIntepreter>>transferTo:from:
> self assertValidExecutionPointe: instructionPointer r:
> framePointer s: stackPointer.

In the StackInterpreter, as in the context Interpreter the next bytecode is fetched by pre-incrementing the instructionPointer and then fetching the byte it points to. Hence it may point to before the first bytecode and hence the + 1 above. 1 is subtracted from a context's pc (2 actually cuz pc is 1-relative and instructionPointer is 0-relative) to derive instructionPointer.

In the Cog VM instructionPointer may also be a machine code pc. So rather than add one, which only makes sense for interpreted methods, the CoInterpreter's assertValidExecutionPointer:s: allows for the - 1 if a frame us interpreted. The StackInterpreter's method predates the CoInterpreter.

I was just wandering in the vicinity of this again, and had a new query...

What is the semantic difference in the naming of the arguments (i.e. lsp<=> lisp and lfp<=>lifp)

between.... ?

StackInterpreter >> assertValidExecutionPointe: lip r: lfp s: lsp imbar: inInterpreter line: ln

CoInterpreter >> assertValidExecutionPointe: lip r: lifp s: lisp imbar: inInterpreter line: ln

because search/replacing makes it easier to diff the two methods...

https://www.diffchecker.com/CL32EXql

This shows the StackInterpreter method refactored slightly to extract "methodField" variable similar to the CoInterpreter

making it easier to compare the two, i.e. red-line-16 and green-line-18 are identical,

but red-line-13 and green-line-14 set "methodField" using different messages, which however have identical definitions.

StackInterpreter >> frameMethod: theFP

<inline: true>

<var: #theFP type: #'char *'>

^stackPages longAt: theFP + FoxMethod

CoInterpreter >> frameMethodField: theFP

<inline: true>

<var: #theFP type: #'char *'>

^stackPages longAt: theFP + FoxMethod

Would it be reasonable to change red-line-13 to send #frameMethodField:

instead? Hopefully my slight rearrangement of the asserts in red okay.

cheers -ben