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