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Re: commit: ldap/servers/slapd/back-ldbm attr.c
> Modified Files:
> attr.c 1.33 -> 1.34
Also back-ldap/bind.c 1.52 -> 1.53, back-bdb/attr.c 1.13 -> 1.14
> Log Message:
> Fix AVL comparisons
> - return desc - a->ai_desc;
> + return (unsigned)desc - (unsigned)a->ai_desc;
I don't know what this is supposed to fix, but:
(a) Both new and original code gives the wrong result or signals an
overflow for pointers to memory locations that are more than
INT_MAX bytes or so apart.
(b) Pointer comparison is only defined between pointers to the same
array. The result of the original code is undefined if desc and
a->ai_desc point to the results of different malloc operations.
(c) The result of casting a pointer to an integer is implementation-
defined. I think it might e.g. return 42 for any pointer.
There is no way to fix all three problems.
This fixes (a) and (c):
if (desc < a->ai_desc)
return (desc != a-ai_desc);
This has a better chance than the committed code of fixing (a) and (b),
but can still fail if pointers are wider than unsigned long:
if ((unsigned long)desc < (unsigned long)a->ai_desc)
return ((unsigned long)desc != (unsigned long)a-ai_desc);
Take your pick. I vote for fixing (a) and (c) since that at least fixes
these problems completely, which the fix for (b) is not guaranteed. If
we meet an implementation where (b) is a problem, we can fix (b), or
rewrite these functions completely so they don't compare pointers at
all, with or without casts to integers.