Re: bit wise math? Is there a function to easily return the bits?
| From: | Richard Lynch | Date: | Thu, 25 Jan 2007 23:29:30 +0000 |
| Subject: | Re: bit wise math? Is there a function to easily return the bits? | ||
| References: | 1 2 | Groups: | php.general |
| Request: | Send a blank email to php-general+get-247798@lists.php.net to get a copy of this message | ||
On Thu, January 25, 2007 1:34 pm, Jon Anderson wrote:
> function bits($num) {
> $bit_array = str_split(strrev(decbin(intval($num))));
> $val_array = array();
> foreach ($bit_array as $pow => $bit) {
> if ($val = $bit * pow(2,$pow))
> $val_array[] = $val;
> }
> return($val_array);
> }
>
> (I wanted to see if I could write it in few LOC.) I wonder if there's
> a
> faster way...
//these might be marginally faster...
function bits($num){
$bits = array();
$bin = decbin(intval($num));
$v = 1;
for ($b = strlen($bin) - 1; $b >= 0; $b--){
if ($bin[$b] === '1') $bits[] = $v;
$v = $v * 2;
}
return $bits;
}
function bits($num){
$num = (int) $num;
$v = 1;
$bits = array();
while ($v <= $num){
if ($v & $num) $bits[] = $v;
$v = $v * 2;
}
return $bits;
}
I suspect there is a much faster way, somewhere, somehow...
>
> jon
>
> blackwater dev wrote:
>> Is there a php function I can call to pass in a number and get the
>> values
>> returned?
>>
>> For example, pass in 7 and get 1,2,4 ?
>>
>> Thanks!
>>
>
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