[Larceny-users] error peeking short values from raw memory

[Felix Klock]

Marco-

On Jul 3, 2009, at 2:28 PM, Marco Maggi wrote:

> "Felix Klock" wrote:
>> Why  are   you  subtracting   2  here  when   you've  been
>> subtracting 1 in all the other cases?
>
> The form producing buggy output is:
>
>> (let ((v (- (expt 2 15) 1)))
>> (%poke16 a v)
>> (write (list v (%peek16 a)))
>> (newline))
>
> which prints (32767 -32769)  where I expected (32767 32767).
> This one:
>
>> (let ((v (- (expt 2 15) 2)))
>> (%poke16 a v)
>> (write (list v (%peek16 a)))
>> (newline))
>
> correctly prints  (32766 32766), I included it  to show that
> the problem is only with 2^15-1.

Ah, I understand now.  I did not read all the output you had included  
carefully enough.

This looks like a fence-post error in the definition of %get16 in lib/ 
Base/std-ffi.sch to me, especially if one compares it to %get32  
immediately following...

-Felix