Re: Integer representation (Was: Re: Maximum size that an array can hold in C++)
* Bart van Ingen Schenau:
[cross-posted to comp.lang.c++ and comp.std.c++]
Alf P. Steinbach wrote:
* Bart van Ingen Schenau:
Alf P. Steinbach wrote:
* Bart van Ingen Schenau:
Pascal J. Bourguignon wrote:
Bart van Ingen Schenau <bart@ingen.ddns.info> writes:
The standard states so in 4.7/2: "If the destination type is
unsigned, the resulting valu is the least unsigned integer
congruent to the source integer (modulo 2^n where n is the number
of bits used to represent the unsigned type)."
If the machine represents unsigned integers as 10-digits BCD
numbers, then the number of bits used to represent the unsigned is
10*log(10)/log(2) = 33.2192809488...
If we take n=34, 2^34 > 10^10 so it's not possible. If we take
n=33, 2^33 < 10^10 so 2^n is not the greatest unsigned integer
(10^10-1).
Oops!
As I quoted the C++ standard literally, this only shows that there
is an unwritten assumption in the standard. This unwritten
assumption is that a pure binary value-representation is used for
(at least) unsigned integer types.
That requirement is explicitly stated in the standard.
Could you give a reference?
James just did else-thread. :-)
No he didn't. He stated what we "know" to be true: that a binary
representation is needed for the integer types. But he did not provide
C&V for the clause that actually says so.
He did.
James quoted: "the representations of integral types shall define values
by use of a pure binary numeration system."
Searching for the last 3 words of that quote, in the standard, lands
you at ?3.9.1/7.
Hah, I'm much better at searching than you!
Yay! :-)
I am not contesting the knowledge that integers must have a pure binary
representation, but I am troubled by the fact that I am unable to locate
this requirement in the standard.
Perhaps the folks in comp.std.c++ can help [me] in locating the clause
that I keep missing.
Posting there you'd just have me answering your question again.
It would be rather silly to trust me more, or less, depending on the
forum, or depending on which hat I'm wearing at the moment.
Cheers & hth.,
- Alf
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