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%%% A (simple) diff
%%% Copyright (C) 2011 Tomas Abrahamsson
%%% Author: Tomas Abrahamsson <>
%%% This library is free software; you can redistribute it and/or
%%% modify it under the terms of the GNU Library General Public
%%% License as published by the Free Software Foundation; either
%%% version 2 of the License, or (at your option) any later version.
%%% This library is distributed in the hope that it will be useful,
%%% but WITHOUT ANY WARRANTY; without even the implied warranty of
%%% Library General Public License for more details.
%%% You should have received a copy of the GNU Library General Public
%%% License along with this library; if not, write to the Free
%%% Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
-export([diff/2, diff/3, patch/2]).
-export([diff_files/2, diff_files/3]).
-export([diff_binaries/2, diff_binaries/3]).
diff_files(F1, F2) -> diff_files(F1, F2, _Opts=[]).
diff_files(F1, F2, Opts) ->
{ok,B1} = file:read_file(F1),
{ok,B2} = file:read_file(F2),
diff_binaries(B1, B2, Opts).
diff_binaries(B1, B2) -> diff_binaries(B1, B2, _Opts=[]).
diff_binaries(B1, B2, Opts) ->
diff(split_bin_to_lines(B1), split_bin_to_lines(B2), Opts).
split_bin_to_lines(B) -> sbtl(binary_to_list(B), "", []).
sbtl("\n" ++ Rest, L, Acc) -> sbtl(Rest, "", [lists:reverse("\n"++L) | Acc]);
sbtl([C|Rest], L, Acc) -> sbtl(Rest, [C|L], Acc);
sbtl("", "", Acc) -> lists:reverse(Acc);
sbtl("", L, Acc) -> lists:reverse([lists:reverse(L) | Acc]).
print_diff_lines(Diff) -> io:format("~s~n", [format_diff_lines(Diff)]).
format_diff_lines(Diff) -> fdl(Diff, 1,1).
fdl([{del,Ls1},{ins,Ls2}|T], X, Y) ->
Addr = io_lib:format("~sc~s~n", [fmt_addr(X,Ls1), fmt_addr(Y, Ls2)]),
Del = format_lines("< ", Ls1),
Sep = io_lib:format("---~n", []),
Ins = format_lines("> ", Ls2),
[Addr, Del, Sep, Ins | fdl(T, X+length(Ls1), Y+length(Ls2))];
fdl([{del,Ls}|T], X, Y) ->
Addr = io_lib:format("~w,~wd~w~n", [X,X+length(Ls), Y]),
Del = format_lines("< ", Ls),
[Addr, Del | fdl(T, X+length(Ls), Y)];
fdl([{ins,Ls}|T], X, Y) ->
Addr = io_lib:format("~wa~w,~w~n", [X,Y,Y+length(Ls)]),
Ins = format_lines("> ", Ls),
[Addr, Ins | fdl(T, X, Y+length(Ls))];
fdl([{eq,Ls}|T], X, Y) ->
fdl(T, X+length(Ls), Y+length(Ls));
fdl([], _X, _Y) ->
fmt_addr(N, Ls) when length(Ls) == 1 -> f("~w", [N]);
fmt_addr(N, Ls) -> f("~w,~w", [N,N+length(Ls)-1]).
f(F,A) -> lists:flatten(io_lib:format(F,A)).
format_lines(Indicator, Lines) ->
lists:map(fun(Line) -> io_lib:format("~s~s", [Indicator, Line]) end,
%% diff(Sx, Sy) -> Diff
%% diff(Sx, Sy, Opts) -> Diff
%% Sx = Sy = [Elem] %% typically a list of lines, characters or words
%% Elem = term()
%% Opts = []
%% Diff = [D]
%% D = {eq, [Elem]} | %% [Elem] is equal in Sx and Sy
%% {ins,[Elem]} | %% [Elem] must be inserted into Sx to create Sy
%% {del,[Elem]} %% [Elem] must be removed from Sx to create Sy
%% Algorithm: "An O(ND) Difference Algorithm and Its Variations"
%% by E. Myers, 1986.
%% Some good info can also be found at
%% General principle of the algorithm:
%% We are about to produce a diff (or editscript) on what differs (or
%% how to get from) string Sx to Sy. We lay out a grid with the
%% symbols from Sx on the x-axis and the symbols from Sy on the Y
%% axis. The first symbol of Sx and Sy is at (0,0).
%% (The Sx and Sy are strings of symbols: lists of lines or lists of
%% characters, or lists of works, or whatever is suitable.)
%% Example: Sx="aXcccXe", Sy="aYcccYe" ==> the following grid is formed:
%% Sx
%% aXcccXe
%% Sy a\
%% Y
%% c \\\
%% c \\\
%% c \\\
%% Y
%% e \
%% Our plan now is go from corner to corner: from (0,0) to (7,7).
%% We can move diagonally whenever the character on the x-axis and the
%% character on the y-axis are identical. Those are symbolized by the
%% \-edges in the grid above.
%% When it is not possible to go diagonally (because the characters on
%% the x- and y-axis are not identical), we have to go horizontally
%% and vertically. This corresponds to deleting characters from Sx and
%% inserting characters from Sy.
%% Definitions (from the "O(ND) ..." paper by E.Myers):
%% * A D-path is a path with D non-diagonal edges (ie: edges that are
%% vertical and/or horizontal).
%% * K-diagonal: the diagonal such that K=X-Y
%% (Thus, the 0-diagonal is the one starting at (0,0), going
%% straight down-right. The 1-diagonal is the one just to the right of
%% the 0-diagonal: starting at (1,0) going straight down-right.
%% There are negative diagonals as well: the -1-diagonal is the one starting
%% at (0,1), and so on.
%% * Snake: a sequence of only-diagonal steps
%% The algorithm loops over D and over the K-diagonals:
%% D = 0..(length(Sx)+length(Sy))
%% K = -D..D in steps of 2
%% For every such K-diagonal, we choose between the (D-1)-paths
%% whose end-points are currently on the adjacent (K-1)- and
%% (K+1)-diagonals: we pick the one that have gone furthest along
%% its diagonal.
%% This means taking that (D-1)-path and going right (if
%% we pick the (D-1)-path on the (K-1)-diagonal) or down (if we
%% pick the (D-1)-path on the (K+1)-diagonal), thus forming a
%% D-path from a (D-1)-path.
%% After this, we try to extend the snake as far as possible along
%% the K-diagonal.
%% Note that this means that when we choose between the
%% (D-1)-paths along the (K-1)- and (K+1)-diagonals, we choose
%% between two paths, whose snakes have been extended as far as
%% possible, ie: they are at a point where the characters Sx and
%% Sy don't match.
%% Note that with this algorithm, we always do comparions further
%% right into the strings Sx and Sy. The algorithm never goes towards
%% the beginning of either Sx or Sy do do further comparisons. This is
%% good, because this fits the way lists are built in functional
%% programming languages.
diff(Sx, Sy) -> diff(Sx, Sy, _Opts=[]).
diff(Sx, Sy, Opts) ->
SxLen = length(Sx),
SyLen = length(Sy),
DMax = SxLen + SyLen,
Tracer = proplists:get_value(algorithm_tracer, Opts, no_tracer),
EditScript = case try_dpaths(0, DMax, [{0, 0, Sx, Sy, []}], Tracer) of
no -> [{del,Sx},{ins,Sy}];
{ed,EditOpsR} -> edit_ops_to_edit_script(EditOpsR)
t_final_script(Tracer, EditScript),
try_dpaths(D, DMax, D1Paths, Tracer) when D =< DMax ->
t_d(Tracer, D),
case try_kdiagonals(-D, D, D1Paths, [], Tracer) of
{ed, E} -> {ed, E};
{dpaths, DPaths} -> try_dpaths(D+1, DMax, DPaths, Tracer)
try_dpaths(_, _DMax, _DPaths, _Tracer) ->
try_kdiagonals(K, D, D1Paths, DPaths, Tracer) when K =< D ->
DPath = if D == 0 -> hd(D1Paths);
true -> pick_best_dpath(K, D, D1Paths)
case follow_snake(DPath) of
{ed, E} ->
{ed, E};
{dpath, DPath2} when K =/= -D ->
t_dpath(Tracer, DPath2),
try_kdiagonals(K+2, D, tl(D1Paths), [DPath2 | DPaths], Tracer);
{dpath, DPath2} when K =:= -D ->
t_dpath(Tracer, DPath2),
try_kdiagonals(K+2, D, D1Paths, [DPath2 | DPaths], Tracer)
try_kdiagonals(_, D, _, DPaths, Tracer) ->
t_exhausted_kdiagonals(Tracer, D),
{dpaths, lists:reverse(DPaths)}.
follow_snake({X, Y, [H|Tx], [H|Ty], Cs}) -> follow_snake({X+1,Y+1, Tx,Ty,
[{e,H} | Cs]});
follow_snake({_X,_Y,[], [], Cs}) -> {ed, Cs};
follow_snake({X, Y, [], Sy, Cs}) -> {dpath, {X, Y, [], Sy, Cs}};
follow_snake({X, Y, oob, Sy, Cs}) -> {dpath, {X, Y, oob, Sy, Cs}};
follow_snake({X, Y, Sx, [], Cs}) -> {dpath, {X, Y, Sx, [], Cs}};
follow_snake({X, Y, Sx, oob, Cs}) -> {dpath, {X, Y, Sx, oob, Cs}};
follow_snake({X, Y, Sx, Sy, Cs}) -> {dpath, {X, Y, Sx, Sy, Cs}}.
pick_best_dpath(K, D, DPs) -> pbd(K, D, DPs).
pbd( K, D, [DP|_]) when K==-D -> go_inc_y(DP);
pbd( K, D, [DP]) when K==D -> go_inc_x(DP);
pbd(_K,_D, [DP1,DP2|_]) -> pbd2(DP1,DP2).
pbd2({_,Y1,_,_,_}=DP1, {_,Y2,_,_,_}) when Y1 > Y2 -> go_inc_x(DP1);
pbd2(_DP1 , DP2) -> go_inc_y(DP2).
go_inc_y({X, Y, [H|Tx], Sy, Cs}) -> {X, Y+1, Tx, Sy, [{y,H}|Cs]};
go_inc_y({X, Y, [], Sy, Cs}) -> {X, Y+1, oob, Sy, Cs};
go_inc_y({X, Y, oob, Sy, Cs}) -> {X, Y+1, oob, Sy, Cs}.
go_inc_x({X, Y, Sx, [H|Ty], Cs}) -> {X+1, Y, Sx, Ty, [{x,H}|Cs]};
go_inc_x({X, Y, Sx, [], Cs}) -> {X+1, Y, Sx, oob, Cs};
go_inc_x({X, Y, Sx, oob, Cs}) -> {X+1, Y, Sx, oob, Cs}.
edit_ops_to_edit_script(EditOps) -> e2e(EditOps, _Acc=[]).
e2e([{x,C}|T], [{ins,R}|Acc]) -> e2e(T, [{ins,[C|R]}|Acc]);
e2e([{y,C}|T], [{del,R}|Acc]) -> e2e(T, [{del,[C|R]}|Acc]);
e2e([{e,C}|T], [{eq,R}|Acc]) -> e2e(T, [{eq, [C|R]}|Acc]);
e2e([{x,C}|T], Acc) -> e2e(T, [{ins,[C]}|Acc]);
e2e([{y,C}|T], Acc) -> e2e(T, [{del,[C]}|Acc]);
e2e([{e,C}|T], Acc) -> e2e(T, [{eq, [C]}|Acc]);
e2e([], Acc) -> Acc.
patch(S, Diff) -> p2(S, Diff, []).
p2(S, [{eq,T}|Rest], Acc) -> p2_eq(S, T, Rest, Acc);
p2(S, [{ins,T}|Rest], Acc) -> p2_ins(S, T, Rest, Acc);
p2(S, [{del,T}|Rest], Acc) -> p2_del(S, T, Rest, Acc);
p2([],[], Acc) -> lists:reverse(Acc).
p2_eq([H|S], [H|T], Rest, Acc) -> p2_eq(S, T, Rest, [H|Acc]);
p2_eq(S, [], Rest, Acc) -> p2(S, Rest, Acc).
p2_ins(S, [H|T], Rest, Acc) -> p2_ins(S, T, Rest, [H|Acc]);
p2_ins(S, [], Rest, Acc) -> p2(S, Rest, Acc).
p2_del([H|S], [H|T], Rest, Acc) -> p2_del(S, T, Rest, Acc);
p2_del(S, [], Rest, Acc) -> p2(S, Rest, Acc).
t_final_script(no_tracer, _) -> ok;
t_final_script(Tracer, EditScript) -> Tracer({final_edit_script, EditScript}).
t_d(no_tracer, _) -> ok;
t_d(Tracer, D) -> Tracer({d,D}).
t_dpath(no_tracer, _) -> ok;
t_dpath(Tracer, DPath) -> Tracer({dpath,DPath}).
t_exhausted_kdiagonals(no_tracer, _) -> ok;
t_exhausted_kdiagonals(Tracer, D) -> Tracer({exhausted_kdiagonals, D}).