add IPv6 prefixLengthFromSubnetMask

Fixes #59
whitequark · Jul 4, 2017 · 9a275c3 · 9a275c3
1 parent 9e22317
commit 9a275c3
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Showing 4 changed files with 96 additions and 4 deletions.
diff --git a/ipaddr.min.js b/ipaddr.min.js
diff --git a/lib/ipaddr.js b/lib/ipaddr.js
@@ -339,6 +339,47 @@
       return new ipaddr.IPv4([high >> 8, high & 0xff, low >> 8, low & 0xff]);
     };
 
+    IPv6.prototype.prefixLengthFromSubnetMask = function() {
+      var cidr, i, k, part, stop, zeros, zerotable;
+      zerotable = {
+        0: 16,
+        32768: 15,
+        49152: 14,
+        57344: 13,
+        61440: 12,
+        63488: 11,
+        64512: 10,
+        65024: 9,
+        65280: 8,
+        65408: 7,
+        65472: 6,
+        65504: 5,
+        65520: 4,
+        65528: 3,
+        65532: 2,
+        65534: 1,
+        65535: 0
+      };
+      cidr = 0;
+      stop = false;
+      for (i = k = 7; k >= 0; i = k += -1) {
+        part = this.parts[i];
+        if (part in zerotable) {
+          zeros = zerotable[part];
+          if (stop && zeros !== 0) {
+            return null;
+          }
+          if (zeros !== 16) {
+            stop = true;
+          }
+          cidr += zeros;
+        } else {
+          return null;
+        }
+      }
+      return 128 - cidr;
+    };
+
     return IPv6;
 
   })();

diff --git a/src/ipaddr.coffee b/src/ipaddr.coffee
@@ -302,6 +302,46 @@ class ipaddr.IPv6
 
     return new ipaddr.IPv4([high >> 8, high & 0xff, low >> 8, low & 0xff])
 
+  # returns a number of leading ones in IPv6 address, making sure that
+  # the rest is a solid sequence of 0's (valid netmask)
+  # returns either the CIDR length or null if mask is not valid
+  prefixLengthFromSubnetMask: ->
+    # number of zeroes in octet
+    zerotable =
+      0    : 16
+      32768: 15
+      49152: 14
+      57344: 13
+      61440: 12
+      63488: 11
+      64512: 10
+      65024: 9
+      65280: 8
+      65408: 7
+      65472: 6
+      65504: 5
+      65520: 4
+      65528: 3
+      65532: 2
+      65534: 1
+      65535: 0
+
+    cidr = 0
+    # non-zero encountered stop scanning for zeroes
+    stop = false
+    for i in [7..0] by -1
+      part = @parts[i]
+      if part of zerotable
+        zeros = zerotable[part]
+        if stop and zeros != 0
+          return null
+        unless zeros == 16
+          stop = true
+        cidr += zeros
+      else
+        return null
+    return 128 - cidr
+
 # IPv6-matching regular expressions.
 # For IPv6, the task is simpler: it is enough to match the colon-delimited
 # hexadecimal IPv6 and a transitional variant with dotted-decimal IPv4 at