Merge pull request #46 from cloudcosmonaut/feat/make-host-count-rfc-compliant

feat: remember the network and broadcast address

Author: bschaatsbergen

README.md

@@ -33,23 +33,30 @@ This also works with IPv6 addresses, for example:
 ```
 $ cidr contains 2001:db8:1234:1a00::/106 2001:db8:1234:1a00::
 true
-``` 
+```
 
 ### Count distinct host addresses
 
 To get all distinct host addresses part of a given CIDR range:
 
 ```
 $ cidr count 10.0.0.0/16
-65536
+65534
 ```
 
-This also works with IPv6 addresses, for example:
+Or with large prefixes like point-to-point links:
+
+```
+$ cidr count count 172.16.18.0/31
+2
+```
+
+This also works with very small CIDR ranges, like a point-to-point link:
 
 ```
 $ cidr count 2001:db8:1234:1a00::/106
 4194304
-``` 
+```
 
 ### CIDR range intersection
 
@@ -65,9 +72,9 @@ This also works with IPv6 addresses, for example:
 ```
 $ cidr overlaps 2001:db8:1111:2222:1::/80 2001:db8:1111:2222:1:1::/96
 true
-``` 
+```
 
 ## Contributing
 
-Contributions are highly appreciated and always welcome. 
+Contributions are highly appreciated and always welcome.
 Have a look through existing [Issues](https://github.com/bschaatsbergen/cidr/issues) and [Pull Requests](https://github.com/bschaatsbergen/cidr/pulls) that you could help with.

pkg/core/core.go

@@ -6,7 +6,18 @@ import (
 
 func AddressCount(network *net.IPNet) uint64 {
 	prefixLen, bits := network.Mask.Size()
-	return 1 << (uint64(bits) - uint64(prefixLen))
+
+	// Check if network is IPv4 or IPv6
+	if network.Mask != nil {
+		// Handle edge cases
+		switch prefixLen {
+			case 32: return 1
+			case 31: return 2
+		}
+	}
+
+	// Remember to subtract the network address and broadcast address
+	return 1 << (uint64(bits) - uint64(prefixLen)) - 2
 }
 
 func ParseCIDR(network string) (*net.IPNet, error) {