File 2111-erl_tar-Slightly-optimize-extraction-from-tar-files.patch of Package erlang

From 906b706191b209afa29b1830ad6f928ad105593b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Tue, 8 Mar 2022 15:16:02 +0100
Subject: [PATCH] erl_tar: Slightly optimize extraction from tar files

Running eprof when extracting tar files revealed that the top CPU
time consumers in the erl_tar process itself (that is, not processes
doing file IO) were checksum calculation and parsing of octal numbers.

This commit optimizes those functions. It turned out that the
checksum is calculated in two different ways, although the second
signed checksum is only neeeded if the first checksum is incorrect
(when extracting very old tar files).
---
 lib/stdlib/src/erl_tar.erl | 57 +++++++++++++++++++++-----------------
 1 file changed, 32 insertions(+), 25 deletions(-)

diff --git a/lib/stdlib/src/erl_tar.erl b/lib/stdlib/src/erl_tar.erl
index c689be30d8..0602edf8cf 100644
--- a/lib/stdlib/src/erl_tar.erl
+++ b/lib/stdlib/src/erl_tar.erl
@@ -1019,11 +1019,14 @@ do_get_format({error, _} = Err, _Bin) ->
 do_get_format(#header_v7{}=V7, Bin)
   when is_binary(Bin), byte_size(Bin) =:= ?BLOCK_SIZE ->
     Checksum = parse_octal(V7#header_v7.checksum),
-    Chk1 = compute_checksum(Bin),
-    Chk2 = compute_signed_checksum(Bin),
-    if Checksum =/= Chk1 andalso Checksum =/= Chk2 ->
+    IsBadChecksum = case compute_checksum(Bin) of
+                        Checksum -> false;
+                        _ -> compute_signed_checksum(Bin) =/= Checksum
+                    end,
+    case IsBadChecksum of
+        true ->
             ?FORMAT_UNKNOWN;
-       true ->
+        false ->
             %% guess magic
             Ustar = to_ustar(V7, Bin),
             Star = to_star(V7, Bin),
@@ -1203,6 +1206,9 @@ compute_signed_checksum(<<H1:?V7_CHKSUM/binary,
 
 %% Returns the checksum of a binary.
 checksum(Bin) -> checksum(Bin, 0).
+
+checksum(<<A/unsigned,B/unsigned,C/unsigned,D/unsigned,Rest/binary>>, Sum) ->
+    checksum(Rest, Sum+A+B+C+D);
 checksum(<<A/unsigned,Rest/binary>>, Sum) ->
     checksum(Rest, Sum+A);
 checksum(<<>>, Sum) -> Sum.
@@ -1251,39 +1257,40 @@ parse_numeric(<<First, _/binary>> = Bin) ->
             parse_octal(Bin)
     end.
 
-parse_octal(Bin) when is_binary(Bin) ->
+parse_octal(<<Bin/binary>>) ->
     %% skip leading/trailing zero bytes and spaces
-    do_parse_octal(Bin, <<>>).
-do_parse_octal(<<>>, <<>>) ->
-    0;
-do_parse_octal(<<>>, Acc) ->
-    case io_lib:fread("~8u", binary:bin_to_list(Acc)) of
-        {error, _} -> throw({error, invalid_tar_checksum});
-        {ok, [Octal], []} -> Octal;
-        {ok, _, _} -> throw({error, invalid_tar_checksum})
-    end;
-do_parse_octal(<<$\s,Rest/binary>>, Acc) ->
+    do_parse_octal(Bin, 0).
+
+do_parse_octal(<<$\s, Rest/binary>>, Acc) ->
     do_parse_octal(Rest, Acc);
 do_parse_octal(<<0, Rest/binary>>, Acc) ->
     do_parse_octal(Rest, Acc);
 do_parse_octal(<<C, Rest/binary>>, Acc) ->
-    do_parse_octal(Rest, <<Acc/binary, C>>).
+    Digit = C - $0,
+    case Digit band 7 of
+        Digit ->
+            do_parse_octal(Rest, Acc bsl 3 bor Digit);
+        _ ->
+            throw({error, invalid_tar_checksum})
+    end;
+do_parse_octal(<<>>, Acc) ->
+    Acc.
 
 parse_string(Bin) when is_binary(Bin) ->
-    do_parse_string(Bin, <<>>).
-do_parse_string(<<>>, Acc) ->
-    case unicode:characters_to_list(Acc) of
+    N = strlen(Bin, 0),
+    <<Prefix:N/binary,_/binary>> = Bin,
+    case unicode:characters_to_list(Prefix) of
         Str when is_list(Str) ->
             Str;
         {incomplete, _Str, _Rest} ->
-            binary:bin_to_list(Acc);
+            binary_to_list(Bin);
         {error, _Str, _Rest} ->
             throw({error, {bad_header, invalid_string}})
-    end;
-do_parse_string(<<0, _/binary>>, Acc) ->
-    do_parse_string(<<>>, Acc);
-do_parse_string(<<C, Rest/binary>>, Acc) ->
-    do_parse_string(Rest, <<Acc/binary, C>>).
+    end.
+
+strlen(<<>>, N) -> N;
+strlen(<<0, _/binary>>, N) -> N;
+strlen(<<_, Rest/binary>>, N) -> strlen(Rest, N + 1).
 
 convert_header(Bin, #reader{pos=Pos}=Reader)
   when byte_size(Bin) =:= ?BLOCK_SIZE, (Pos rem ?BLOCK_SIZE) =:= 0 ->
-- 
2.34.1