RE: Where does the C standard describe overflow of signed integers?

["Dave Korn" <dave.korn@artimi.com>]

----Original Message----
>From: Georg Bauhaus
>Sent: 15 July 2005 14:21

> You can have both, correctness and uninitialised local
> variables. For an impression of the difference in performance,
> and for a way to ensure correctness, I tried this
> (switch register/volatile in the declaration lines in comp
> and r to see the effects).

  I didn't get that far.  Before the first call to comp the program has
already accessed uninitialised memory:

> int main()
> {
>   short buffer[BUFFER_SIZE];
>   int result;
> 
>   assert(ITERATIONS > 0);

  So far, so good.  Declare some uninitialised storage.

> 
>   for (int runs = 0; runs < ITERATIONS; ++runs) {

  First time round, runs = 0;

>     result = r(buffer, BUFFER_SIZE);

  Call function 'r'.

> /* pre: a has elements, that is hi > 0. Frequently called */
> int r(short a[], size_t hi)
> {
>   //register int x, y, z;
>   volatile int x=1, y=2, z=3;

  x=1, y=2 and =3.  hi = BUFFER_SIZE and a[] is uninitialised.

> 
>   assert(hi > 0);

  Still good...
 
>   for (size_t c=0; c < hi + 2; ++c) {
>     if (a[c]) {

  Uninitialised variable access.  Boom.  *NOT* correct.

  In what sense of the word 'correct' do you claim this example is correct?


    cheers,
      DaveK
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