[M3devel] overshift/overflow

[Jay K]

Tony, these two questions seemed to go unanswered:

 

1)

 

What should this code do:

 

 

Word.LeftShift(..., 100); (* where 100 >= BITSIZE(INTEGER),

 and similar for Long.LeftShift and shift >= BITSIZE(LONGINT) *)

 

 

I think m3front should generate a warning

and then either generate the same code as today,

or something smaller where it only generates code

to issue the runtime error.

The warning is missing.

"Generating the code same as today" is harder on backends,

since they have to check for this condition and handle it somehow,

though it doesn't matter much what they do, since the runtime

error generation will always run and anything after it never will.



2) What should this code do:

 

 

EVAL -FIRST(INTEGER);

 

 

I believe the frontend should issue a warning.

And then generate the same code as today.

Just the warning is missing.

 

 

 

3) Aside, and not a question.

I believe, esp. at this point, the notion that overflow checking is a per-thread setting

is a mistake. It has "never" been used, save on a small number of targets.

It is too late to foist that change on any code thread-wide.

The correct thing to do is introduce different interfaces/modules/types/functions

which either always do overflow checking, or, perhaps but less likely,

new interfaces/modules/types/functions that are runtime configurable, as

INTEGER was originally speced.

 

 

Even the original spec not so great in my opinion.

There are too many things to code correctly, let alone worrying about "this"

possibly varying underneath you. The overall system is too much a combination

of different code to expect just because one set of code wants integer overflow

to be an error, that all the code can deal with that.

Better to have separate interfaces/functions/types for the different functionality.

 

 

 

 - Jay
 		 	   		  
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