How to convert a valid dotted decimal netmask into the corresponding CIDR prefix length
Jan 17th, 2009 by paolo
Yesterday I was googling to find the algorithm to covert a netmask (in the dotted decimal format like 255.255.255.0) in corresponding cidr to manage a database migration, but I can't find it. So I wrote it in PHP.
The following function takes a valid netmask in the dotted decimal format as a string in input and returns the corresponding cidr prefix length as int:
PHP:
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function netmask2cidr($netmask) {
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$cidr = 0;
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for (;$number> 0; $number = ($number <<1) % 256) {
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$cidr++;
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}
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}
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return $cidr;
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}
