From 02abeffc9d753b5fcd1ce7da93f437887f574bad Mon Sep 17 00:00:00 2001
From: Dan Gudmundsson <dgud@erlang.org>
Date: Fri, 21 Aug 2015 13:13:17 +0200
Subject: Optimize zip:unzip/2 when uncompressing to memory

Optimize the case where we are appending to the end of the binary, use
binary syntax to create binaries with room for expansion in the next
loop, instead of using iolist_to_binary which creates a binary of the
exact size and needs to be copied in each loop.

Also remove support the unused Acc as iolists.
---
 lib/stdlib/src/zip.erl | 68 ++++++++++++++++----------------------------------
 1 file changed, 22 insertions(+), 46 deletions(-)

(limited to 'lib/stdlib')

diff --git a/lib/stdlib/src/zip.erl b/lib/stdlib/src/zip.erl
index d6031dabbc..bec0bd3f6d 100644
--- a/lib/stdlib/src/zip.erl
+++ b/lib/stdlib/src/zip.erl
@@ -1550,57 +1550,33 @@ unix_extra_field_and_var_from_bin(_) ->
 
 %% A pwrite-like function for iolists (used by memory-option)
 
-split_iolist(B, Pos) when is_binary(B) ->
-    split_binary(B, Pos);
-split_iolist(L, Pos) when is_list(L) ->
-    splitter([], L, Pos).
-
-splitter(Left, Right, 0) ->
-    {Left, Right};
-splitter(Left, [A | Right], RelPos) when is_list(A) or is_binary(A) ->
-    Sz = erlang:iolist_size(A),
-    case Sz > RelPos of
-	true ->
-	    {Leftx, Rightx} = split_iolist(A, RelPos),
-	    {[Left | Leftx], [Rightx, Right]};
-	_ ->
-	    splitter([Left | A], Right, RelPos - Sz)
-    end;
-splitter(Left, [A | Right], RelPos) when is_integer(A) ->
-    splitter([Left, A], Right, RelPos - 1);
-splitter(Left, Right, RelPos) when is_binary(Right) ->
-    splitter(Left, [Right], RelPos).
+pwrite_binary(B, Pos, Bin) when byte_size(B) =:= Pos ->
+    append_bins(Bin, B);
+pwrite_binary(B, Pos, Bin) ->
+    erlang:iolist_to_binary(pwrite_iolist(B, Pos, Bin)).
 
-skip_iolist(B, Pos) when is_binary(B) ->
-    case B of
-	<<_:Pos/binary, Bin/binary>> -> Bin;
-	_ -> <<>>
-    end;
-skip_iolist(L, Pos) when is_list(L) ->
-    skipper(L, Pos).
-
-skipper(Right, 0) ->
-    Right;
-skipper([A | Right], RelPos) when is_list(A) or is_binary(A) ->
-    Sz = erlang:iolist_size(A),
-    case Sz > RelPos of
-	true ->
-	    Rightx = skip_iolist(A, RelPos),
-	    [Rightx, Right];
-	_ ->
-	    skip_iolist(Right, RelPos - Sz)
-    end;
-skipper([A | Right], RelPos) when is_integer(A) ->
-    skip_iolist(Right, RelPos - 1).
+append_bins([Bin|Bins], B) when is_binary(Bin) ->
+    append_bins(Bins, <<B/binary, Bin/binary>>);
+append_bins([List|Bins], B) when is_list(List) ->
+    append_bins(Bins, append_bins(List, B));
+append_bins(Bin, B) when is_binary(Bin) ->
+    <<B/binary, Bin/binary>>;
+append_bins([_|_]=List, B) ->
+    <<B/binary, (iolist_to_binary(List))/binary>>;
+append_bins([], B) ->
+    B.
 
-pwrite_iolist(Iolist, Pos, Bin) ->
-    {Left, Right} = split_iolist(Iolist, Pos),
+pwrite_iolist(B, Pos, Bin) ->
+    {Left, Right} = split_binary(B, Pos),
     Sz = erlang:iolist_size(Bin),
-    R = skip_iolist(Right, Sz),
+    R = skip_bin(Right, Sz),
     [Left, Bin | R].
 
-pwrite_binary(B, Pos, Bin) ->
-    erlang:iolist_to_binary(pwrite_iolist(B, Pos, Bin)).
+skip_bin(B, Pos) when is_binary(B) ->
+    case B of
+	<<_:Pos/binary, Bin/binary>> -> Bin;
+	_ -> <<>>
+    end.
 
 
 %% ZIP header manipulations
-- 
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