source code
% The Computer Language Benchmarks Game
% https://salsa.debian.org/benchmarksgame-team/benchmarksgame/
%% Contributed by Fredrik Svahn based on Per Gustafsson's mandelbrot program
-module(mandelbrot).
-export([main/1]).
-define(LIM_SQR, 4.0).
-define(ITER, 50).
-define(SR, -1.5).
-define(SI, -1).
main([Arg]) ->
N = list_to_integer(Arg),
io:put_chars(["P4\n", Arg, " ", Arg, "\n"]),
%% Spawn one process per row
Row = fun(Y)-> spawn(fun()-> row(0, ?SI+Y*2/N, N, 0, [], 7) end) end,
Pids = lists:map(Row, lists:seq(0,N-1)),
%Pass token around to make sure printouts are in the right order
hd(Pids) ! tl(Pids) ++ [ self() ],
receive _Token -> halt(0) end.
%Iterate over a row, collect bits, bytes and finally print the row
row(X, _, N, Bits, Bytes, BitC) when X =:= N-1 ->
receive Pids ->
put_chars(Bits, Bytes, BitC),
hd(Pids) ! tl(Pids)
end;
row(X, Y2, N, Bits, Bytes, 0) ->
row(X+1, Y2, N, 0, [Bits bsl 1 + m(?ITER, ?SR+X*2/N, Y2) | Bytes], 7);
row(X, Y2, N, Bits, Bytes, BitC) ->
row(X+1, Y2, N, Bits bsl 1 + m(?ITER, ?SR+X*2/N, Y2), Bytes, BitC-1).
%Mandelbrot algorithm
m(Iter, CR,CI) -> m(Iter - 1, CR, CI, CR, CI).
m(Iter, R, I, CR, CI) ->
case R*R+I*I > ?LIM_SQR of
false when Iter > 0 -> m(Iter-1, R*R-I*I+CR, 2*R*I+CI, CR, CI);
false -> 1;
true -> 0
end.
put_chars(_, Bytes, 7)-> io:put_chars(lists:reverse(Bytes));
put_chars(Bits, Bytes, C) -> io:put_chars(lists:reverse([Bits bsl (C+1) | Bytes])).