[M3devel] TextLiteral.MaxBytes again

[Rodney M. Bates]

On 09/05/2013 11:05 AM, Tony Hosking wrote:
> Here is a modest proposal that should resolve this issue.
> Declare TextLiteral.T to have a minimal buf: ARRAY [0..0] OF Byte;
> Then use UNSAFE address arithmetic to access the bytes (TextLiteral.m3 already does the bounds checks explicitly using cnt).
>
> Updated TextLiteral.i3 and TextLiteral.m3 attached.
>

That would address the changing fingerprint problem.

The declaration of buf should have a conspicuous and unambiguous
"Keep your hands off" comment, with explanation why.

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> Antony Hosking | Associate Professor | Computer Science | Purdue University
> 305 N. University Street | West Lafayette | IN 47907 | USA
> Mobile +1 765 427 5484
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> On Sep 5, 2013, at 10:42 AM, "Rodney M. Bates" <rodney_bates at lcwb.coop> wrote:
>
>> There is another issue here.  I want TextLiteral.MaxBytes to get a final size
>> and not change.  Every time it changes, it creates compatibility problems by
>> orphaning any existing pickle files and any compiled programs that write them.
>> It changes the fingerprint, so a recently-compiled reading program can't find the
>> type in its own list of known types.  This also affects network objects when two
>> communicating programs are compiled with different TextLiteral versions.
>>
>> MaxBytes' particular contribution to the type doesn't otherwise matter, because it's
>> artificial, but it still undermines reading pickles.
>>
>> I have been loading up the pickle reading code with hard-coded historical fingerprints
>> of various older versions.  But it's a pain to keep doing, tedious to ferret out the
>> values, and it still only helps those who constantly download and compile the latest
>> CM3.
>>
>> At some point, I am thinking of choosing some likely historical TextLiteral.T fingerprint
>> and hard-coding the compiler to artificially deliver it , rather than the one computed from
>> the version-of-the day of TextLiteral.  But this too would not help those who would
>> rather not constantly download the latest, rebuild the compiler, then recompile their
>> applications.
>>
>> On 09/03/2013 01:02 AM, Jay K wrote:
>>> ok, another question:
>>>
>>>
>>> CONST
>>>   (* DIV BITSIZE should not be here! *)
>>>   (* MaxBytes = LAST (INTEGER) DIV BITSIZE (Byte) - 7 - 8 * ORD(BITSIZE(INTEGER) = 64); *)
>>>   MaxBytes = 16_7FFFFFFF DIV BITSIZE (Byte) - 7 - 8 * ORD(BITSIZE(INTEGER) = 64);
>>>
>>> TYPE
>>>    T = RTHooks.TextLiteral;
>>> REVEAL
>>>    T = TEXT BRANDED "TextLiteral.T" OBJECT
>>>      cnt : INTEGER;
>>>      buf : ARRAY [0..MaxBytes - 1] OF Byte;
>>>    OVERRIDES ...
>>>
>>>
>>> T is a reference type.
>>> Is there a way to state this with no limit?
>>>
>>>
>>> Isn't it already unsafe?
>>> You know -- the array is usually smaller and the compiler is only going to check against this large size.
>>>
>>>
>>>   - Jay
>>
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