53 lines
1.4 KiB
Erlang
53 lines
1.4 KiB
Erlang
%%% File : ecu_misc.erl
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%%% Author : Hans Svensson
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%%% Description : Misc. functionality
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%%% Created : 13 Jan 2022 by Hans Svensson
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-module(ecu_misc).
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-export([eea/2, exp_mod/3,
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hex_to_bin/1, bin_to_hex/1,
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pcomp/1]).
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%% A^B mod P
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exp_mod(_A, 0, _P) -> 1;
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exp_mod(A, B, P) when A > 0 ->
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binary:decode_unsigned(crypto:mod_pow(A, B, P));
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exp_mod(A, B, P) ->
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X = exp_mod(-A, B, P),
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case B rem 2 == 0 orelse X == 0 of
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true -> X;
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false -> P - X
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end.
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%% Extended Euclidean Algorithm
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eea(A, B) when ((A < 1) or (B < 1)) ->
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undefined;
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eea(A, B) ->
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eea(A, 1, 0, B, 0, 1).
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eea(G, S, T, 0, _, _) ->
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{G, S, T};
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eea(G0, S0, T0, G1, S1, T1) ->
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Q = G0 div G1,
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eea(G1, S1, T1, G0 - (Q * G1), S0 - (Q * S1), T0 - (Q * T1)).
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%% Very rudimentary parallel computation...
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pcomp(Fs) ->
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Parent = self(),
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Pids = [ spawn(fun() -> Parent ! {self(), F()} end) || F <- Fs ],
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[ receive {Pid, X} -> X after 500 -> error(timeout) end || Pid <- Pids ].
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%% Hex encode/decode
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-spec hex_to_bin(Input :: string()) -> binary().
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hex_to_bin(S) ->
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hex_to_bin(S, []).
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hex_to_bin([], Acc) ->
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list_to_binary(lists:reverse(Acc));
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hex_to_bin([X,Y|T], Acc) ->
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{ok, [V], []} = io_lib:fread("~16u", [X,Y]),
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hex_to_bin(T, [V | Acc]).
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-spec bin_to_hex(Input :: binary()) -> string().
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bin_to_hex(Bin) ->
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lists:flatten([io_lib:format("~2.16.0B", [X]) || X <- binary_to_list(Bin)]).
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