Re: [Apc-aa-coders] Ids of strange lineths.

[Mitra <mi...@mi...>]

Well spotted!

I get similar results (and those two "huh" should be "huhl", 've got


Array
(
     [16] =3D> 3652
     [15] =3D> 15
)
packed

Array
(
     [32] =3D> 3652
     [30] =3D> 15
)
unpacked

- Mitra


At 2:43 PM +0100 25/1/03, Honza Malik wrote:
>Hi Mitra,
>
>    I did some more testing on ids and now I know, where the problem is.
>The new_id() is OK - it returns allways 32 character long id, but
>sometimes it return id with ...20 at the end. Packed '20' is space and
>this is problem, because if you insert 16 characters long packed id
>ending with space into MySQL and then you get it back, the id is 15
>character long.
>
>MySQL REMOVES ENDING SPACES FROM INSERTED STRING!
>
>I will fix new_id() to not generate such ids.
>
>
>On P=E1, 2003-01-24 at 12:28, Mitra wrote:
>>  Ok - stranger .... my guess was wrong, md5 returns a 32 character
>>  string, which cannot contain 00 or 27 so cannot end up as a shorter
>>  string.
>>
>>  To test, I ran a loop through 99999 samples of new_id, which should
>>  have generated about 400 bad ids by your statistics.
>>
>>  I think the bad ids in your database must be the result of some buggy
>>  earlier code.
>>
>>  Lets try three things.
>>  1: Please check my test - appended at the end of this message.
>
>I test it and all 99999 ids are 32 characters long.
>
>>  2: Please re-run your test, see if the number of bad ids has gone up,
>>  if there is something bad then as long as you have created more than
>>  256 ids then statistically it should have increased by 1 or more.
>
>Increased: [16] =3D> 92254 [15] =3D> 367 [14] =3D> 4
>
>>  3: Please send the code for your test, I'll run it on my installation
>>  and see how many odd length ids I have.
>
>require "include/config.php3";
>require $GLOBALS[AA_INC_PATH]."util.php3";
>require $GLOBALS[AA_INC_PATH]."locsessi.php3";
>
>$db =3D new DB_AA;
>
>$db->query( "SELECT id from item" );
>while($db->next_record()) {
>     $fromdb[$len_p =3D strlen($db->f('id'))]++;
>     $unpdb[$len_u =3D strlen(unpack_id($db->f('id')))]++;
>//    if( $len_p<16 )
>//        echo "<br>".$db->f('id');
>}   
>
>huh($fromdb, 'packed');
>huh($unpdb, 'unpacked');
>
>echo "
>
>        Regards
>                  Honza ";
>
>
>  >
>  > - Mitra
>  >
>  >
>  > At 11:55 PM +0100 22/1/03, Honza Malik wrote:
>  > >  >3) Your assumption that packed ids are EXACTLY 16 characters long (=
and
>>  >  >unpacked are EXACTLY 32 characters long) is unfortunately wrong. I c=
an't
>>  >  >say you why - we generate the ids by new_id() function, but in our
>>  >  >database are packed ids for item 16 (in 91907 items), 15 (366) and 1=
4
>>  >  >(4) characters long.
>>  >
>>  >  Strange - because new_id uses "md5" which has to return 128 bits.
>>  >
>>  >  I wonder if these were ids which generated a leading ascii zero, the
>>  >  ratios look reasonable for this, i.e. 919007/366 =3D 251, which is
>>  >  close to a one in 256 chance, i.e. something that occurred when 8
>>  >  bits (2^8=3D256) all were zero.    This makes sense if we assume that
>>  >  md5 returns a number which the ereg in new_id casts as a string, and
>>  >  so ignores the leading zero.
>>  >
>>  >  I've fixed zids.php3 to allow 12..16 character packed ids, and 24..32
>>  >  long, but this could break my tagged ids. I've also fixed
>>  >  util.php3.new_id to only return a string of exactly 16 chars.
>>  >
>>  >  > >5) In zids.php3 you wrote:
>>  >>  >
>>  >>  >function id_t2l(&$str) {
>>  >>  >#TODO: Look online for quicker way to substr last 32 chars - mitra
>>  >>  >         if (ereg("(.*)([0-9a-f]{32})",$str,$parts))
>>  >>  >                 return $parts[2];
>>  >>  >
>>  >>  >The quicker way is: substr($str, -32), but see 3)
>>  >>
>>  >>  Ok - I'll make this 24..32, and I guess we can't use tags that end i=
n
>>  >>  a hex character [0-9a-f)
>>  >
>>  >Or you can use some delimeter (tag:unpacked_id). As I write before, we
>>  >never use tags so far, so the syntax is on your choice.
>>
>>
>>  require "../include/config.php3";
>>  require $GLOBALS[AA_INC_PATH]."util.php3";
>>
>>  $i =3D 0;
>>  $j=3D 99999;
>>  print "<br>Testing start, loops=3D$j: sample=3D";
>  > $foo =3D new_id();
>>  print $foo;
>>  while ($i++ < $j) {
>>  $foo =3D new_id();
>>  if (strlen($foo) !=3D 32) print "<br>FOO:$i:$foo:strlen=3D".strlen($foo)=
;
>>  if (strlen(pack_id($foo)) !=3D 16) print "<br>FOO:$i:$foo:packed
>>  strlen=3D".strlen(\
>>  pack_id($foo));
>>  }
>>  print "<br>Testing end sample =3D ";
>>  $foo =3D new_id();
>>  print $foo;
>>
>>  print "Done\n";
>>
>
>
>
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-- 
Mitra Technology Consulting -  www.mitra.biz - mi...@mi...
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