Added eqcmini quickcheck library to lib/

lib/eqc/examples/ip_checksum.erl

@@ -0,0 +1,40 @@
+%%% File    : ip_checksum.erl
+%%% Author  : Ulf Norell <ulf.norell@quviq.com>,
+%%%           Thomas Arts <thomas.arts@quviq.com>
+%%% Description : Implementation of IP checksums.
+%%% Created : 7 Jun 2010 by Ulf Norell
+-module(ip_checksum).
+
+-export([checksum/1, checksum/2, sum/2, pad/2, add/2, negate/1]).
+
+checksum(Bin) ->
+  checksum(Bin, 16).
+
+checksum(Bin, N) ->
+  negate(sum(pad(Bin, N), N)).
+
+% Sum a binary of N bit words in ones complement representation.
+sum(Bin, N) ->
+  lists:foldl(fun(A, B) -> add(A, B) end, <<0:N>>,
+              [ <<A:N>> || <<A:N>> <= Bin ]).
+
+% Add two numbers in ones complement representation.
+add(A, B) ->
+  N = bit_size(A),
+  <<X:N>> = A,
+  <<Y:N>> = B,
+  Carry = (X + Y) div (1 bsl N),
+  <<(X + Y + Carry):N>>.
+
+%% invert all bits... as simple as that.
+negate(BitString) ->
+    << <<(1-Bit):1>> || <<Bit:1>> <= BitString >>.
+
+pad(Binary, Bits) ->
+    PaddingLength = 
+	case bit_size(Binary) rem Bits of
+	    0 -> 0;
+	    N -> Bits - N
+	end,
+    <<Binary/bits, 0:PaddingLength>>.
+