[PHP] Re: Can this code go faster?
Just a couple of comments about those 0x.. and 11
in my post.
(By the way, i haven't looked to closely on speed even if the OP asked
for that, i was unsure on how he was coding his numbers).
[EMAIL PROTECTED] (Rolf Østvik) wrote in
news:[EMAIL PROTECTED]:
[EMAIL PROTECTED] (René Fournier) wrote in
news:[EMAIL PROTECTED]:
I need to convert a binary number of arbitrary length to a signed
integer.
If you on the other hand know that the string should represent an 8
bit in two's complement then this could work:
function bin2int ($bin) {
$a = bindec($bin);
$val = ($a | 0x80) ? (0xff00 | $a) : $a;
if the input is a 8 bit signed binary string then bit 7 determine the
sign. 0xff00 will then make this to an 32 signed integer
return $val;
}
function bin2int ($bin) {
if (substr($bin,0,1) == 1) {
// NEGATIVE
$val = bindec(substr(
.$bin,-32));
bindec returns a 32 bit signed integer, i just make sure that the
leftmost bits in the 32 character long string are 1 if the leftmost bit
in the original string is 1.
} else {
// POSITIVE
$val = bindec($bin);
}
return $val;
}
--
Rolf
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[PHP] Re: Can this code go faster?
[EMAIL PROTECTED] (René Fournier) wrote in
news:[EMAIL PROTECTED]:
I need to convert a binary number of arbitrary length to a signed
integer.
This is how I'm doing it now:
CODE
function bin2int ($bin) {
if (substr($bin,0,1) == 1) {
$val = 0 - bindec(substr($bin,1)); // NEGATIVE
} else {
$val = bindec(substr($bin,1)); // POSITIVE
}
}
echo bin2int(1101).'br /';
echo bin2int(10001101);
OUTPUT
13
-13
As you can see, if the most-significant bit is 1, then the rest of the
value is negative. If the first bit is 0, then the rest is positive.
If this is what you want then your numeric representation of negative
numbers is not standard. In that case your function is as good as you can
get.
This is the standard two's complement representation:
1101 is 13
0010 is -13
10001101 is -115
You specify the most-significant bit as sign bit, and that you can have a
arbitrary lenght string representing a binary number.
Then 010 will be different than 10, is that correct?
If you on the other hand know that the string should represent an 8 bit in
two's complement then this could work:
function bin2int ($bin) {
$a = bindec($bin);
$val = ($a | 0x80) ? (0xff00 | $a) : $a;
return $val;
}
// or by using if instead of ? and :
//function bin2int ($bin) {
//$a = bindec($bin);
// if ( $a | 0x80) {
// $val = (0xff00 | $a);
// } else {
// $val =$a;
// }
//
//return $val;
//}
If the string represent a 16 bit number use
$val = ($ | 0x8000) ? (0x | $a) : $a;
If the string represent a 32 bit number use only bindec
If you still want
- a leading 1 to represent a negative number,
- and that the string can have arbitrary lenght,
- but you want correct two's complement representation
then we need something different, e.g:
function bin2int ($bin) {
if (substr($bin,0,1) == 1) {
// NEGATIVE
$val = bindec(substr(.$bin,-32));
} else {
// POSITIVE
$val = bindec($bin);
}
return $val;
}
--
Rolf
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[PHP] Re: collapse SELECT from multiple tables
[EMAIL PROTECTED] (David Christensen) wrote in news:[EMAIL PROTECTED]: I'm trying to figure out the best way to handle a SELECT from multiple tables where a single ID in tableA relates to multiple ID's in tableB: SELECT tableA.ID, tableB.data FROM tableA, tableB WHERE tableA.ID=3 AND tableA.ID=tableB.tableAID What I'm trying to product is an array output similar to: | ID | data | | 3 | data1, data2, data3 | if the table data is represented by this: tableA | ID | something | | 1 | something1 | | 2 | something2 | | 3 | something3 | tableB | ID | tableAID | data | | 1 | 3| data1 | | 2 | 3| data2 | | 3 | 3| data2 | Suggestion 1 and 2 may depend of which database you use. Suggestion 3 have been touched in other answers. Suggestion 1: Create a custom function which takes the tableA.ID as parameter and run a query on tableB and creates an string as answer. I do this in an application i use PostgreSQL. Suggestion 2: Create an aggregate. I havent yet tried this in PostgreSQL. Suggestion 3: Order your sql result and loop over the data. -- Rolf Østvik -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
Re: [PHP] Re: [NEWBIE GUIDE] For the benefit of new members
[EMAIL PROTECTED] (John Nichel) wrote in news:[EMAIL PROTECTED]: Jay Blanchard wrote: [snip] CR Just a thought, but would it be worth someone posting the list CR once a week to catch new users as they sign up? Isn't it posted once a month as it is? [/snip] It used to be, but it seems that it hasn't been posted in a while. So I retrieved it and posted it. I was thinking about setting up a cron to post it every other day or so. Didn't it used to get sent out to people when they subscribed to the list too? Anyone know if that still happens? Well, i only accesses this list on usenet. I haven't subscribed to anything. -- Rolf -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
