OT: Requesting C advice

[Mike McCarty]

Matthew Saltzman wrote:
> On Thu, 24 May 2007, Mike McCarty wrote:
> 

[snip]

>>> developed.  In any case, I don't know of any modern machine that 
>>> doesn't represent negative integers in two's complement.
>>
>>
>> Reach into your pocket, and pull out your calculator.
> 
> 
> Fair enough.  I'll concede the point if you can name a 
> standard-conforming C compiler for my calculator.

You stated that you didn't know of any modern machine. I don't
know of any conforming implementations. Most calculators use
decimal floating point or decimal fixed point. A conforming
implementation would be difficult, since a pure binary representation
is required for integral types.

> H&S note that sign-magnitude and one's complement are permitted, but the 

Any pure binary representation will do.

> Usenet discussions involved subtle arguments that are long lost to (my) 
> memory (as is the final conclusion).  For most of us programming modern 
> general-purpose computers, it's a moot point.
> 
> H&S also state in an example that
> 
>     unsigned u;
> 
>     if ( u > -1 ) ...
> 
> will never execute the if block (because -1 is cast to unsigned before 
> the comparison).  But that's not true for sign-magnitude.

I'd have to go back and read the standard promotion rules before
commenting on this one.

>> Erm, from the Standard:
>>
>> 3.4
>>       [#1] byte
>>       addressable  unit  of  data storage large enough to hold any
>>       member  of  the  basic  character  set  of   the   execution
>>       environment
>>
> 
> OK that was from memory (and at 3am, to boot).  From H&S, a "byte" or 
> "storage unit" is as above, essentially, the smallest independently 
> addressible block of storage.  The char type has a size of one byte. (As 
> I recall, whether a standard-conforming compiler could be written for a 
> word-addressible machine was also a subject of language-lawyer debates 
> on Usenet.)

The Standard does not say what size a byte is. CHAR_BIT defines that.
It is possible for a conforming implementation to have CHAR_BIT to
be 64. A byte does not have to be the smallest independently addressable
unit greater than a bit on the underlying architecture, but it does have
to be the smallest unit to which the implementation provides
addressability which is greater than a bit.

Mike
-- 
p="p=%c%s%c;main(){printf(p,34,p,34);}";main(){printf(p,34,p,34);}
Oppose globalization and One World Governments like the UN.
This message made from 100% recycled bits.
You have found the bank of Larn.
I can explain it for you, but I can't understand it for you.
I speak only for myself, and I am unanimous in that!