53 lines
1.7 KiB
Erlang
53 lines
1.7 KiB
Erlang
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-module(chapter7).
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-export([breverse/1, term_to_packet/1, packet_to_term/1, reverse_byte/1,
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reverse_bits/1, reverse_bitlist/1, test/0]).
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%% Exercises
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%% 1. Write a function that reverses the order of bytes in a binary.
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breverse(Bin) ->
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binary:list_to_bin(lists:reverse(binary:bin_to_list(Bin))).
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%% 2. Write a function term_to_packet(Term) -> Packet that returns a
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%% binary consisting of a 4-byte length header N followed by N
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%% bytes of data produced by calling term_to_binary(Term).
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%% Need to packetize
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term_to_packet(Term) ->
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BinaryTerm = erlang:term_to_binary(Term),
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Length = erlang:byte_size(BinaryTerm),
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<<Length:32, BinaryTerm:Length/bytes>>.
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%% 3. Write the inverse function packet_to_term(Packet) -> Term that
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%% is the inverse of the previous function.
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packet_to_term(<<Length:32, BinaryTerm:Length/bytes>>) ->
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erlang:binary_to_term(BinaryTerm).
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packet_test(Term) ->
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Term = packet_to_term(term_to_packet(Term)).
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%% 4. Write some tests in the style of Adding Tests to Your Code, on
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%% page 46, to test that the previous two functions can correctly
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%% encode terms into packets and recover the original terms by
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%% decoding the packets.
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test() ->
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Squared = fun (X) -> X * X end,
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packet_test(Squared),
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packet_test(32),
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packet_test(<<"Goodbye, Joe.">>),
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<<0:7, 1:1>> = reverse_byte(<<1:1, 0:7>>).
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%% 5. Write a function to reverse the bits in a binary.
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reverse_byte(<<A:1, B:1, C:1, D:1, E:1, F:1, G:1, H:1>>) ->
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<<H:1,G:1,F:1,E:1,D:1,C:1,B:1,A:1>>;
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reverse_byte(<<>>) -> <<>>.
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reverse_bitlist([]) -> [];
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reverse_bitlist([H|T]) ->
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[reverse_byte(H) || reverse_bitlist(T)].
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reverse_bits(Binary) ->
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erlang:list_to_binary(reverse_bitlist(erlang:binary_to_list(Binary))).
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