OpenEuphoria

Re: Strange machine-level exception

• Posted by Daryl Border <darylb5 at aol.com> Jun 20, 2007
• 566 views

Pete Lomax wrote:
> 
> Bernie Ryan wrote:
> > 
> > 
> > Looking at the source in be_runtime.c for find_from.
> > 
> > It seems that the code is testing for the value of the length for
> > 
> > the full sequence instead of the length of the sequence from the
> > 
> > starting point of the find to the end of the sequence.
> > 
> > Maybe I'am wrong ?
> 
> That's what I thought too. A further test confirms this beyond any remaining
> doubt:
> }}}
<eucode>
> sequence x
>  x={1,2,3,4,{5}}
>  x=x[1..3]
> ?find_from({5},x,3)
> </eucode>
{{{

> and it prints 5 which is obvious nonsense as length(x) is now 3.
> 
> Regards,
> Pete

I agree the routine is searching memory beyond the end of the sequence.
There is another problem with both find_from and match_from. Neither
routine performs lower bounds checking on the third argument. If a negative
value is passed to the routines, they will search memory before the beginning
of the sequence which may also crash the interpreter. I also think the routines
should return -1 for an out of bounds condition instead of 0. The current 
behavior makes a return value of 0 ambiguous.