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Date: Sat, 06 Aug 2016 14:14:00 +0200
To: PHP Internals <internals@lists.php.net>
Cc: Xinchen Hui <xinchen.h@zend.com>
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Message-ID: <20160806121401.480605FA95@mx.zeyos.com>
Subject: Re: [PHP-DEV] More packed hash optimizations in array.c
From: ben.coutu@zeyos.com (Benjamin Coutu)

Hi Xinchen,

There is still a way we could make this work, if we'd simply check for nNum=
Used =3D=3D nNumOfElements as well. Because a packed array with nNumUsed eq=
ual to nNumOfElements must be consecutively indexed from zero onward withou=
t any gaps (no IS_UNDEF).

I therefore propose to change array_slice to use:

if ((Z_ARRVAL_P(input)->u.flags & HASH_FLAG_PACKED) && (!preserve_keys || (=
offset =3D=3D 0 && Z_ARRVAL_P(input)->nNumUsed =3D=3D Z_ARRVAL_P(input)->nN=
umOfElements)))

I think the additional check is well worth it as it is not costly per se an=
d will only ever be performed for the case of array_slice($packed_array, 0,=
 ..., true). It won't slow down the more common cases of array_slice($packe=
d_array, ..., false) or array_slice($hash_array, ..., true/false).

That way we can preserve the packed charactersitic even if the input array =
was channelled through array_slice with preserved_keys=3Dtrue, which is not=
 that uncommon given that many APIs use wrappers around array_slice with th=
e preserve_keys option precautiously set to true.

Let me know what you think.

Thanks,

Benjamin