# Canonicalize CIDR

### Using library

```perl
use IP::Addr;
for «87.70.141.1/22 36.18.154.103/12 62.62.197.11/29 67.137.119.181/4 161.214.74.21/24 184.232.176.184/18» -> $cidr {
   say "$cidr -> $(IP::Addr.new($cidr).network)";
}
```

### String manipulation

```perl
#!/usr/bin/env raku
unit sub MAIN(*@cidrs);

if !@cidrs {
  # test data
  @cidrs = «87.70.141.1/22 36.18.154.103/12 62.62.197.11/29 67.137.119.181/4 161.214.74.21/24 184.232.176.184/18»;
}

for @cidrs -> $cidr {
  say "$cidr -> $(canonicalize $cidr)";
}

# canonicalize a CIDR block: make sure none of the host bits are set
sub canonicalize($cidr) {
  # dotted-decimal / bits in network part
  my ($dotted, $size) = $cidr.split: '/';

  # get network part of the IP as binary string
  my $binary = $dotted.split('.')».fmt('%08b').join.substr(0, $size);

  # Add host part with all zeroes
  $binary ~= 0 x (32 - $size);

  # Convert back to dotted-decimal
  my $canon = $binary.comb(8)».parse-base(2).join: '.';

  # And output
  say "$canon/$size";
}
```

#### Output:

```
87.70.141.1/22 -> 87.70.140.0/22
36.18.154.103/12 -> 36.16.0.0/12
62.62.197.11/29 -> 62.62.197.8/29
67.137.119.181/4 -> 64.0.0.0/4
161.214.74.21/24 -> 161.214.74.0/24
184.232.176.184/18 -> 184.232.128.0/18
```

### Bit mask and shift

```perl
# canonicalize a IP4 CIDR block
sub CIDR-IP4-canonicalize ($address) {
  constant @mask = 24, 16, 8, 0;
 
  # dotted-decimal / subnet size
  my ($dotted, $size) = |$address.split('/'), 32;
 
  # get IP as binary address
  my $binary = sum $dotted.comb(/\d+/) Z+< @mask;
 
  # mask off subnet
  $binary +&= (2 ** $size - 1) +< (32 - $size);
 
  # Return dotted-decimal notation
  (@mask.map($binary +> * +& 0xFF).join('.'), $size)
}
 
my @tests = <
  87.70.141.1/22
  36.18.154.103/12
  62.62.197.11/29
  67.137.119.181/4
  161.214.74.21/24
  184.232.176.184/18
  100.68.0.18/18
  10.4.30.77/30
  10.207.219.251/32
  10.207.219.251
  110.200.21/4
  10.11.12.13/8
  10.../8
>;
 
printf "CIDR: %18s  Routing prefix: %s/%s\n", $_, |.&CIDR-IP4-canonicalize
  for @*ARGS || @tests;
```

#### Output:

```
CIDR:     87.70.141.1/22  Routing prefix: 87.70.140.0/22
CIDR:   36.18.154.103/12  Routing prefix: 36.16.0.0/12
CIDR:    62.62.197.11/29  Routing prefix: 62.62.197.8/29
CIDR:   67.137.119.181/4  Routing prefix: 64.0.0.0/4
CIDR:   161.214.74.21/24  Routing prefix: 161.214.74.0/24
CIDR: 184.232.176.184/18  Routing prefix: 184.232.128.0/18
CIDR:     100.68.0.18/18  Routing prefix: 100.68.0.0/18
CIDR:      10.4.30.77/30  Routing prefix: 10.4.30.76/30
CIDR:  10.207.219.251/32  Routing prefix: 10.207.219.251/32
CIDR:     10.207.219.251  Routing prefix: 10.207.219.251/32
CIDR:       110.200.21/4  Routing prefix: 96.0.0.0/4
CIDR:      10.11.12.13/8  Routing prefix: 10.0.0.0/8
CIDR:            10.../8  Routing prefix: 10.0.0.0/8
```


---

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