Re: Fix disable-checking bootstrap problem on ppc-darwin

[Geoffrey Keating <geoffk at apple dot com>]

On Aug 24, 2004, at 5:12 PM, Richard Henderson wrote:

> On Tue, Aug 24, 2004 at 05:45:57PM -0400, Andrew MacLeod wrote:
> > Is it strictly necessary for the VUSE operands to be sorted in order 
> > for
> > this comparison to be true? Someone who knows more about what causes
> > various VUSEs to be created might answer that better.
>
> I've sort of lost track of this thread.  Is the argument for sorting
> the VUSEs that we have hashes that are applied to them, and thus we
> need to have the hashes come out the same?

More generally, that we need to compare them and we desire (not need, 
as far as I can tell) the comparisons to be equal when the lists 
contain the same elements.

> If true, another solution is to ensure that for any commutative
> operation that we're hashing, that we use a commutative hash.  So
> instead of always
>
> 	for each operand (op) {
> 	  hash <<= n;
> 	  hash ^= munge(op);
> 	}
>
> do
>
> 	if (commutative (operation)) {
> 	  hash <<= n;
> 	  hash ^= munge(operation);
> 	  for each operand (op) {
> 	    hash += munge(op);
> 	  }
> 	} else {
> 	  ...
> 	}

This works for the _hash function, but the _eq function still needs to 
somehow work out whether the two lists are really equivalent or just 
happen to have the same hash value.

Attachment: smime.p7s
Description: S/MIME cryptographic signature