stdlib: Optimize handling of Unicode in the string module

The unicode_util:cp() function handles deep lists faster by returning
the rest of the input more balanced to the right than before.

1 files changed, 24 insertions, 8 deletions

diff --git a/lib/stdlib/test/string_SUITE.erl b/lib/stdlib/test/string_SUITE.erl
index 251e09121c..fe01900c55 100644
--- a/lib/stdlib/test/string_SUITE.erl
+++ b/lib/stdlib/test/string_SUITE.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %% 
-%% Copyright Ericsson AB 2004-2018. All Rights Reserved.
+%% Copyright Ericsson AB 2004-2019. All Rights Reserved.
 %% 
 %% Licensed under the Apache License, Version 2.0 (the "License");
 %% you may not use this file except in compliance with the License.
@@ -754,19 +754,22 @@ do_measure(DataDir) ->
     io:format("~p~n",[byte_size(Bin)]),
     Do = fun(Name, Func, Mode) ->
                  {N, Mean, Stddev, _} = time_func(Func, Mode, Bin, 20),
-                 io:format("~15w ~6w ~6.2fms ±~5.2fms #~.2w gc included~n",
+                 io:format("~15w ~11w ~8.2fms ±~6.2fms #~.2w gc included~n",
                            [Name, Mode, Mean/1000, Stddev/1000, N])
          end,
     Do2 = fun(Name, Func, Mode) ->
                   {N, Mean, Stddev, _} = time_func(Func, binary, <<>>, 20),
-                  io:format("~15w ~6w ~6.2fms ±~5.2fms #~.2w gc included~n",
+                  io:format("~15w ~11w ~8.2fms ±~6.2fms #~.2w gc included~n",
                             [Name, Mode, Mean/1000, Stddev/1000, N])
           end,
+    %% lefty_list means a list balanced to the left, like
+    %% [[[30],31],32]. Only some functions check such lists.
+    Modes = [list, lefty_list, binary],
     io:format("----------------------~n"),
 
     Do(old_tokens, fun(Str) -> string:tokens(Str, [$\n,$\r]) end, list),
     Tokens = {lexemes, fun(Str) -> string:lexemes(Str, [$\n,$\r]) end},
-    [Do(Name,Fun,Mode) || {Name,Fun} <- [Tokens], Mode <- [list, binary]],
+    [Do(Name,Fun,Mode) || {Name,Fun} <- [Tokens], Mode <- Modes],
 
     S0 = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxy.....",
     S0B = <<"xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxy.....">>,
@@ -824,17 +827,17 @@ do_measure(DataDir) ->
 
     io:format("--~n",[]),
     NthTokens = {nth_lexemes, fun(Str) -> string:nth_lexeme(Str, 18000, [$\n,$\r]) end},
-    [Do(Name,Fun,Mode) || {Name,Fun} <- [NthTokens], Mode <- [list, binary]],
+    [Do(Name,Fun,Mode) || {Name,Fun} <- [NthTokens], Mode <- Modes],
     Do2(take_t, repeat(fun() -> string:take(S0, [$.,$y], false, trailing) end), list),
     Do2(take_t, repeat(fun() -> string:take(S0B, [$.,$y], false, trailing) end), binary),
     Do2(take_tc, repeat(fun() -> string:take(S0, [$x], true, trailing) end), list),
     Do2(take_tc, repeat(fun() -> string:take(S0B, [$x], true, trailing) end), binary),
 
     Length = {length, fun(Str) -> string:length(Str) end},
-    [Do(Name,Fun,Mode) || {Name,Fun} <- [Length], Mode <- [list, binary]],
+    [Do(Name,Fun,Mode) || {Name,Fun} <- [Length], Mode <- Modes],
 
     Reverse = {reverse, fun(Str) -> string:reverse(Str) end},
-    [Do(Name,Fun,Mode) || {Name,Fun} <- [Reverse], Mode <- [list, binary]],
+    [Do(Name,Fun,Mode) || {Name,Fun} <- [Reverse], Mode <- Modes],
 
     ok.
 
@@ -1064,7 +1067,20 @@ time_func(N,Sum,SumSq, _, _, Res, _) ->
     {N, Mean, Stdev, Res}.
 
 mode(binary, Bin) -> Bin;
-mode(list, Bin) -> unicode:characters_to_list(Bin).
+mode(list, Bin) -> unicode:characters_to_list(Bin);
+mode(lefty_list, Bin) ->
+    L = unicode:characters_to_list(Bin),
+    to_left(L).
+
+to_left([]) ->
+    [];
+to_left([H|L]) ->
+    to_left([H], L).
+
+to_left(V, []) ->
+    V;
+to_left(V, [H|L]) ->
+    to_left([V,H], L).
 
 %%
 %% Old string lists Test cases starts here.