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Fix the internals of our hash functions to used unsigned values during hash

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computation as the overflow behavior of signed integers is undefined.

In practice we require compiling everything with -fwrapv which forces overflow
to be defined as twos compliment but this keeps the code cleaner for checkers
or in the case where someone has compiled it without -fwrapv or their
compiler's equivalent.

Found by Clang trunk's Undefined Behavior Sanitizer (UBSan).

Cleanup only - no functionality or hash values change.
This commit is contained in:
Gregory P. Smith 2012-12-10 18:15:46 -08:00
parent 90555d0f0d
commit 27cbcd6241
5 changed files with 14 additions and 14 deletions
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10
Objects/tupleobject.c
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@ -315,11 +315,11 @@ error:
static Py_hash_t
tuplehash(PyTupleObject *v)
{
register Py_hash_t x, y;
register Py_uhash_t x, y; /* Unsigned for defined overflow behavior. */
register Py_ssize_t len = Py_SIZE(v);
register PyObject **p;
Py_hash_t mult = _PyHASH_MULTIPLIER;
x = 0x345678L;
Py_uhash_t mult = _PyHASH_MULTIPLIER;
x = 0x345678UL;
p = v->ob_item;
while (--len >= 0) {
y = PyObject_Hash(*p++);
@ -327,9 +327,9 @@ tuplehash(PyTupleObject *v)
return -1;
x = (x ^ y) * mult;
/* the cast might truncate len; that doesn't change hash stability */
mult += (Py_hash_t)(82520L + len + len);
mult += (Py_uhash_t)(82520UL + len + len);
}
x += 97531L;
x += 97531UL;
if (x == -1)
x = -2;
return x;