Re: [BLACKBOX] Conversion & Casting

From: Campbell, Robert (SELEX GALILEO, UK) <robert.d.campbell{([at]})nowhere.xy>
Date: Tue, 26 Oct 2010 08:54:46 +0100

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>> >-----Original Message-----
>> >From: BlackBox [mailto:BLACKBOX{([at]})nowhere.xy
>> >Sent: Tuesday, 26 October 2010 7:41 AM
>> >To: BLACKBOX{([at]})nowhere.xy
>> >Subject: [BLACKBOX] Conversion & Casting

>> >On 21/10/2010 23:32, Chris Burrows wrote:

>> >What (*does*) SYSTEM.VAL do when the input and output have
>> >differing numbers of
>> >bits?


>> I did a quick test and found that BlackBox happily compiles and runs
>> something like the following:
>>
>> TYPE
>> String = ARRAY 256 OF CHAR;
>>
>> VAR
>> s: String;
>> i: INTEGER;
>> ...
>> ...
>> s := '123';
>> i := SYSTEM.VAL(INTEGER, s);
>>
>> The resulting value of i is 00320031H so it looks like it's
>> just typecast
>> the first corresponding number of bits.
>>
>> I've made a mental note to be even more careful in future when using
>> SYSTEM.VAL ;-)


An interesting partial answer.

What about:

VAR
  b : BYTE;
  s : SET;
BEGIN
  b := SYSTEM.VAL(BYTE, s);
  s := SYSTEM.VAL(SET, b);


In the first line which byte of s is taken?. I guess there is no
definitive answer, a separate experiment needs to be done for each
compiler.


In the second line where is b put, and what goes into the rest of s?
This is more difficult because if an experiment says b is padded with
zeros
we do not know if this is deliberate, and thus repeatable, or accidental
and maybe
not repeatable.


Even if SYSTEM.VAL varies from compiler to compiler, it would be good if
it were documented
for each compiler.


Cheers

Robert
SELEX Galileo Ltd
Registered Office: Sigma House, Christopher Martin Road, Basildon, Essex SS14 3EL
A company registered in England & Wales. Company no. 02426132
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Received on Tue Oct 26 2010 - 09:54:46 UTC