Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:58418
Mailing-List: contact internals-help@lists.php.net; run by ezmlm
Received-SPF: error (pb1.pair.com: domain yahoo.com from 98.139.91.79 cause and error)
DomainKey-Status: good
DomainKey-Signature:a=rsa-sha1; q=dns; c=nofws;
  s=s1024; d=yahoo.com;
  h=X-YMail-OSG:Received:X-Mailer:References:Message-ID:Date:From:Reply-To:Subject:To:In-Reply-To:MIME-Version:Content-Type;
  b=M01c8DYtbN9sX7rZ9KtGucdNxQLfshNeinT98wd4TY6RgM1HvQ0OwiHEsDIFi4mLEyJxTIr2Ts6inU+SF/ffpo4Q3GAeVGc1q6QAED4YDGy1l6KGR2JO880EnxFa9QDMla1pf4bq3VbWD5x4sUNV23T8ClSHIYlNxD2ftAZrqUE=;
References: <1330618943.51670.YahooMailNeo@web43505.mail.sp1.yahoo.com> <op.wah3g22nidpuyk@slws007.slhq.int>
Message-ID: <1330622765.21753.YahooMailNeo@web43507.mail.sp1.yahoo.com>
Date: Thu, 1 Mar 2012 09:26:05 -0800 (PST)
Reply-To: Adi Mutu <adi_mutu06@yahoo.com>
To: Gustavo Lopes <glopes@nebm.ist.utl.pt>,
  "internals@lists.php.net" <internals@lists.php.net>
In-Reply-To: <op.wah3g22nidpuyk@slws007.slhq.int>
MIME-Version: 1.0
Content-Type: multipart/alternative; boundary="686268854-80020659-1330622765=:21753"
Subject: Re: [PHP-DEV] question about Zend MM 
From: adi_mutu06@yahoo.com (Adi Mutu)

--686268854-80020659-1330622765=:21753
Content-Type: text/plain; charset=iso-8859-1
Content-Transfer-Encoding: quoted-printable

=0A=0A=0AAh, now i got it......so it can also return size, if size is direc=
tly a multiple of =A0ZEND_MM_ALIGNMENT.=0AI was convinced that it has to be=
 stricly > than size, i guess i was wrong.=0A=0A=0A________________________=
________=0A From: Gustavo Lopes <glopes@nebm.ist.utl.pt>=0ATo: Adi Mutu <ad=
i_mutu06@yahoo.com>; internals@lists.php.net =0ASent: Thursday, March 1, 20=
12 6:44 PM=0ASubject: Re: [PHP-DEV] question about Zend MM =0A =0AOn Thu, 0=
1 Mar 2012 17:22:23 +0100, Adi Mutu <adi_mutu06@yahoo.com> wrote:=0A=0A> I =
want to understand how Zend MM works, so i'm looking trought the sources an=
d i see this:=0A> =0A> #define ZEND_MM_ALIGNMENT_MASK ~(ZEND_MM_ALIGNMENT-1=
) #define ZEND_MM_ALIGNED_SIZE(size)=A0=A0=A0 (((size) + ZEND_MM_ALIGNMENT =
- 1) & ZEND_MM_ALIGNMENT_MASK)=0A> =0A> =0A> I understand that the first de=
fine will create something like 11111000 ( it will clear last 3 bits)=0A> b=
ut what does the 2nd define? Before clearing the last 3 bytes why does it a=
dd ZEND_MM_ALIGNMENT- 1=0A> to size?=0A> =0A=0AIt basically just rounds to =
the next multiple of ZEND_MM_ALIGNMENT, assuming ZEND_MM_ALIGNMENT is a pow=
er of 2.=0A=0AZEND_MM_ALIGNMENT is a power of 2, so it has 1 bit set. Subtr=
acting 1 will zero that bit and and flip on all the other less significant =
bits. Then negating flips the bits so that now the bits less significant th=
an the log2(ZEND_MM_ALIGNMENT)-th will be zero and the others will be one.=
=0A=0AZEND_MM_ALIGNED_SIZE adds ZEND_MM_ALIGNMENT - 1 and applies the mask.=
 The effect is that the result will be >=3D size and it will be a multiple =
of ZEND_MM_ALIGNMENT (in particular the smallest multiple of ZEND_MM_ALIGNM=
ENT that's >=3D the argument) because the bits less significant than the lo=
g2(ZEND_MM_ALIGNMENT)-th will be zero. "a & n-1" is the same as "a mod n" w=
ith n being a power of 2. So if a & ZEND_MM_ALIGNMENT - 1 =3D=3D 0 then a m=
od ZEND_MM_ALIGNMENT =3D=3D 0 and a is a multiple of ZEND_MM_ALIGNMENT.=0A=
=0A--Gustavo Lopes
--686268854-80020659-1330622765=:21753--