Hi Jakub,
----- Original Message -----
From: "Jakub Zelenka"
Sent: Tuesday, August 18, 2015
On Tue, Aug 18, 2015 at 9:48 PM, Matt Wilmas <php_li...@realplain.com>
wrote:
Hi Anatol, Jakub,
[...]
The checks with zend_long vars like key_length and iterations are
impossible when ZEND_LONG_MAX == INT_MAX (most if not all 32-bit, I
guess). So those checks should already be removed by the compiler.
I was thinking that compiler should be able to optimize it out but not
sure
about all compilers that we support. It's quite cheap so can do that
anyway
but not sure if it's worthy it.
If any compiler can't do such a simple optimization, then it's going to be
missing many other possible optimizations as well. Read: Who cares about
them. :-)
But for the size_t ones, would need to check SIZEOF_SIZE_T > 4 around the
macros or such. Or you could just change in the definition:
if (_max < _var)
to
if (sizeof(_max) < sizeof(_var) && _max < _var)
Which should work fine and allow the compiler to remove it easily,
without
any extra clutter.
we are talking about size_t (unsigned) and int (signed) so not sure how
could compiler optimize it out on 32bit? Did I miss anything?
sizeof(INT_literal_or_var) should be equal (not <) to sizeof(size_t_var) on
32-bit (if ints are 32-bit). So the condition becomes (4 < 4 && _max <
_var) and is optimized out. The signedness doesn't matter, and we don't
care in this case, but the compiler can't otherwise know that...
Of course on 64-bit, only (_max < _var) remains -- (4 < 8) is removed.
BTW, in openssl_pbkdf2(), it looks like the if (!digest) check can be
moved up after EVP_get_digestbyname() as well...?
I'm not really sure if there is any point to optimize this at all.
PKCS5_PBKDF2_HMAC
is quite expensive function ( it is a kdf creating hmac in iterations
rounds ) and any such optimization in PHP will be just too small compare
to
that overhead... But I can of course move it and I might do that.. :) Just
think that there is not much point to spend time on optimizing these
functions. I think that OpenSSL overhead (also for most other functions)
will be just too big compare to these micro optimizations... ;)
Yeah, I know, I was just sayin'. :-D Since I assumed EVP_sha1()'s return
value didn't need to be checked, that's all (I don't know anything about
it!).
Cheers
Jakub
- Matt
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