54 lines
1.9 KiB
Erlang
54 lines
1.9 KiB
Erlang
-module(bitwise_io).
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-compile([export_all]).
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%% Erlang allows for easy manipulation of bitstrings. Here I'll
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%% present a function that can take a message of 8-bit ASCII
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%% characters and remove the MSB, leaving the same message in 7-bits.
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compress(Message) ->
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<< <<X:7>> || <<X:8>> <= Message >>.
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%% Here we decompress the message.
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decompress(Message) ->
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<< <<X:8>> || <<X:7>> <= Message >>.
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%% Now a test to demonstrate that this conversion works:
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test_bitstring_conversion() ->
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Message = <<"Hello, Rosetta Code!">>,
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io:format("~p: ~B~n",[Message, bit_size(Message)]),
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Compressed = compress(Message),
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io:format("~p: ~B~n",[Compressed, bit_size(Compressed)]),
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Decompressed = decompress(Compressed),
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io:format("~p: ~B~n",[Decompressed, bit_size(Decompressed)]),
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io:format("~p = ~p ? ~p~n",[Message, Decompressed,
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Message =:= Decompressed]).
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%% Now to show this on file output, we'll write the compressed version
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%% to a file. Now, erlang's file:write_file expects objects that are
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%% multiples of 8bits. We'll add padding to allow the writing to
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%% complete, and then discard the padding when reading the file back
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%% in.
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test_file_io() ->
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Message = <<"Hello, Rosetta Code!">>,
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FileName = "bitwise_io.dat",
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Compressed = compress(Message),
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PaddingSize = (8 - (bit_size(Compressed) rem 8)) rem 8,
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PaddedCompressed = <<Compressed:(bit_size(Compressed))/bitstring,
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0:PaddingSize>>,
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file:write_file(FileName,PaddedCompressed),
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{ok, ReadIn} = file:read_file(FileName),
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UnpaddedSize = bit_size(ReadIn) - 7,
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Unpadded =
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case UnpaddedSize rem 7 =:= 0 of
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true ->
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<<T:(UnpaddedSize)/bitstring,_:7>> = ReadIn,
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T;
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false ->
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<< <<X:7>> || <<X:7>> <= ReadIn >>
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end,
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Decompressed = decompress(Unpadded),
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io:format("~p~n",[Decompressed]).
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