As a consequence of a heavy discussion in another thread,
I wrote this program:
#include <stdlib.h>
int main(void)
{
char *p=calloc(65521 ,65552);
if (p)
printf("BUG!!!! \n");
}
The multiplication will give an erroneus result
in 32 bit size_t systems. I have tested this
in several systems with several compilers.
Maybe people with other compilers/implementations
would compile this program and send the results?
The results I have so far are:
LINUX
GCC 2.95
HAS THE BUG
GCC-4.02
NO BUGS
GCC-3.x
NO BUGS
WINDOWS
cygwin gcc 3.4.4
NO bugs
pelles c:
HAS THE BUG
Microsoft
Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 14.00.50727.42
for 80x86
NO BUGS (If the multiplication overflows it will trap. Very good
behavior)
AIX
IBM-cc (compiling in 32 bit mode)
NO BUGS
gcc 4.0.0 (compiling in 32 bit mode)
NO BUGS
Thanks in advance for your cooperation
Jan 2 '07
149  4313 
On Wed, 03 Jan 2007 09:58:35 +0100, av wrote:
>the "problem" is not in calloc or malloc but it is in the mathemaical
model ("modello matematico") used for size_t
possible i'm the only one in think that standard C is wrong on
definition of size_t?
av said:
On Wed, 03 Jan 2007 09:58:35 +0100, av wrote:
>>the "problem" is not in calloc or malloc but it is in the mathemaical
model ("modello matematico") used for size_t
possible i'm the only one in think that standard C is wrong on
definition of size_t?
That's unlikely. There are plenty of people who don't understand C.
--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999 http://www.cpax.org.uk
email: rjh at the above domain, - www.
av wrote:
On Wed, 03 Jan 2007 09:58:35 +0100, av wrote:
>>the "problem" is not in calloc or malloc but it is in the mathemaical
model ("modello matematico") used for size_t
possible i'm the only one in think that standard C is wrong on
definition of size_t?
Yes.
--
Chris "first on the Underground!" Dollin
"No-one here is exactly what he appears." G'kar, /Babylon 5/
In article <2v************ *************** *****@4ax.com>, av <av@ala.awrot e:
>possible i'm the only one in think that standard C is wrong on
definition of size_t?
Certainly the modular arithmetic used for unsigned types is usually
inappropriate for sizes, but so are signed types. And presumably the
standards committee would not be willing to invent a new kind of
integer for this purpose.
-- Richard
--
"Considerat ion shall be given to the need for as many as 32 characters
in some alphabets" - X3.4, 1963.
Richard Tobin said:
In article <2v************ *************** *****@4ax.com>, av <av@ala.a>
wrote:
>>possible i'm the only one in think that standard C is wrong on
definition of size_t?
Certainly the modular arithmetic used for unsigned types is usually
inappropriate for sizes,
Why?
but so are signed types. And presumably the
standards committee would not be willing to invent a new kind of
integer for this purpose.
And it's easy to see why not, if you try doing so for yourself. What
characteristics should such an integer type have?
--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999 http://www.cpax.org.uk
email: rjh at the above domain, - www.
In article <vI************ *************** ***@bt.com>,
Richard Heathfield <rj*@see.sig.in validwrote:
>Certainly the modular arithmetic used for unsigned types is usually
inappropriat e for sizes,
>Why?
Because the space required for A bytes and B bytes is A+B bytes, not
(A+B) mod (SIZE_MAX+1).
>but so are signed types. And presumably the
standards committee would not be willing to invent a new kind of
integer for this purpose.
>And it's easy to see why not
Yes.
-- Richard
--
"Considerat ion shall be given to the need for as many as 32 characters
in some alphabets" - X3.4, 1963.
On Thu, 11 Jan 2007 12:31:53 +0100, av wrote:
>On Wed, 03 Jan 2007 09:58:35 +0100, av wrote:
>>the "problem" is not in calloc or malloc but it is in the mathemaical
model ("modello matematico") used for size_t
possible i'm the only one in think that standard C is wrong on
definition of size_t?
because i have some time to troll, here it is the right model for your
"beloved" ssize_t and size_t
------------------------------------------
Signed
int32_t a,b;
/ INT32_MIN, if a or b or both are INT32_MIN
/ INT32_MIN, if the result is not the usual mathematic result
a@b=v{
\ mathematical correct result
where @ is in { +, -, *, /, %}
If i want to see if the computatiton that use +-*/%
is correct is enought to prove
result is in [INT32_MIN+1..IN T32_MAX]
------------------------------------------
unsigned
uns32_t a, b;
/ UNS32_MAX, if a or b or both are UNS32_MAX
/ UNS32_MAX, if the result is not the usual mathematic result
a@b=v{
\ mathematical correct result
where @ is in { +, -, *, /, %, <<, >>, &, |, ~}
If i want to see if the computatiton that use +-*/%<<>>&|~
is correct is enought to prove
result is in [0..UNS32_MAX-1]
------------------------------------------
i say i trolling because i'm not sure to be right
can i say only that it seems to me useful
Richard Tobin said:
In article <vI************ *************** ***@bt.com>,
Richard Heathfield <rj*@see.sig.in validwrote:
>>Certainly the modular arithmetic used for unsigned types is usually
inappropria te for sizes,
>>Why?
Because the space required for A bytes and B bytes is A+B bytes, not
(A+B) mod (SIZE_MAX+1).
Sure, but at some point you have to accept that A+B doesn't make sense. It
may well be that implementations need to supply a wider size_t than they do
at present, but when all's said and done, there are (according to
Schneier's "Applied Cryptography", 2nd edition) only 2^265 atoms in the
Universe (not including dark matter). If we could store a megabyte of data
in each atom (ha! why not?), that would be 2^285 bytes, right? So if we had
a 285-bit size_t, it would be able to store the sum total of the sizes of
all the objects it is possible to create in a Universe-sized computer, so
there is simply no point in having a size_t wider than that (unless you're
into parallel universes). If we confine ourselves to the Earth, we have a
mere 2^170 atoms to play with, so - even given that rather optimistic
megabyte per atom - a 190-bit size_t would do the trick nicely, and modular
arithmetic would become rather irrelevant.
We live in a real world with real limits, and it's high time that computer
programmers got used to the fact.
--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999 http://www.cpax.org.uk
email: rjh at the above domain, - www.
Richard Heathfield <rj*@see.sig.in validwrites:
We live in a real world with real limits, and it's high time that computer
programmers got used to the fact.
But integers are *so* much easier!
--
int main(void){char p[]="ABCDEFGHIJKLM NOPQRSTUVWXYZab cdefghijklmnopq rstuvwxyz.\
\n",*q="kl BIcNBFr.NKEzjwC IxNJC";int i=sizeof p/2;char *strchr();int putchar(\
);while(*q){i+= strchr(p,*q++)-p;if(i>=(int)si zeof p)i-=sizeof p-1;putchar(p[i]\
);}return 0;}
In article <eb************ *********@bt.co m>,
Richard Heathfield <rj*@see.sig.in validwrote:
>Because the space required for A bytes and B bytes is A+B bytes, not
(A+B) mod (SIZE_MAX+1).
>Sure, but at some point you have to accept that A+B doesn't make sense.
I'm not really arguing that size_t ought to be a different type, just
agreeing with someone that it has a problem. And we've seen that this
problem is not illusory, because several implementations have a bug in
calloc() because of it.
There are various ways it could be improved, some more and some less
C-like:
- use an arbitrary-precision type. Handy, but not really C.
- use a larger but fixed-size integer type. This is happening anyway
with 64-bit systems, but is still susceptible to the calloc() mistake.
- use an integer type that is required to signal overflow. This
seems like a plausible extension.
The overflow-signalling solution seems like a good idea to me; I imagine
the main problem is that it is not efficient to implement on all systems.
>We live in a real world with real limits, and it's high time that computer
programmers got used to the fact.
Having programming languages check these limits has advantages.
-- Richard
--
"Considerat ion shall be given to the need for as many as 32 characters
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