INADA Naoki added the comment:
Raymond, I understand your worries. I won't commit this until I do more
precise survey.
But why I trying this is not only I find duplicated code.
I think benefit of this technique is reduced by historical reason.
In Python 2.7, there are only two lookup functions: lookdict and
lookdict_string.
Both functions support dict containing dummy entry.
In the first comparing part in the lookdict_string():
if (ep->me_key == NULL || ep->me_key == key)
return ep;
if (ep->me_key == dummy)
freeslot = ep;
else {
if (ep->me_hash == hash && _PyString_Eq(ep->me_key, key))
return ep;
freeslot = NULL;
}
And similar code in same function but in loop:
if (ep->me_key == NULL)
return freeslot == NULL ? ep : freeslot;
if (ep->me_key == key
|| (ep->me_hash == hash
&& ep->me_key != dummy
&& _PyString_Eq(ep->me_key, key)))
return ep;
if (ep->me_key == dummy && freeslot == NULL)
freeslot = ep;
First part can ignore freeslot variable is NULL or not. But second lookup
can't.
Since most lookup is done at first try, this technique may had significant
effect.
But for now, we're having five lookdict functions (if we include
lookdict_index).
Three of them (lookdict_unicode_nodummy, lookdict_split, and lookdict_index)
cares only dict without dummies.
They don't have freeslot variable. So first part and second part is almost
same.
Performance benefit from this technique may be negligible.
About remaining two functions (lookdict_unicode and lookdict), this technique
may have still effect.
But performance of them are not so important now, compared with Python 2.7.
They were used for all name lookup in Python 2.7, but they are fallback of
lookdict_split and lookdict_unicode_nodummy now.
On the other hand, having 2.5x (2 -> 5) lookdict function means maintenance
cost of duplicated code is increased.
At first, I'll start three functions which doesn't take care of dummies.
I think there are almost zero performance regression.
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<http://bugs.python.org/issue29304>
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