From d14f1512b01261c1cfdff2effe587118d9ddc012 Mon Sep 17 00:00:00 2001
From: Mikael Pettersson <mikpelinux@gmail.com>
Date: Mon, 25 Sep 2017 22:11:28 +0200
Subject: base64:decode(Binary) optimized reimplementation

---
 lib/stdlib/src/base64.erl | 70 +++++++++++++++++++++++------------------------
 1 file changed, 35 insertions(+), 35 deletions(-)

(limited to 'lib/stdlib/src/base64.erl')

diff --git a/lib/stdlib/src/base64.erl b/lib/stdlib/src/base64.erl
index 6e96f7d1f7..c8cf6fdffe 100644
--- a/lib/stdlib/src/base64.erl
+++ b/lib/stdlib/src/base64.erl
@@ -113,7 +113,7 @@ encode_binary(Bin) ->
       Data :: ascii_binary().
 
 decode(Bin) when is_binary(Bin) ->
-    decode_binary(<<>>, Bin);
+    decode_binary(Bin, <<>>);
 decode(List) when is_list(List) ->
     decode_list(List, <<>>).
 
@@ -186,31 +186,41 @@ mime_decode_to_string(List) when is_list(List) ->
 	 bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,
 	 bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad}).
 
-decode_binary(Result0, <<C:8,T0/bits>>) ->
-    case element(C, ?DECODE_MAP) of
-	bad ->
-	    erlang:error({badarg,C});
-	ws ->
-	    decode_binary(Result0, T0);
-	eq ->
-	    case strip_ws(T0) of
-		<<$=:8,T/binary>> ->
-		    <<>> = strip_ws(T),
-		    Split = byte_size(Result0) - 1,
-		    <<Result:Split/bytes,_:4>> = Result0,
-		    Result;
-		T ->
-		    <<>> = strip_ws(T),
-		    Split = byte_size(Result0) - 1,
-		    <<Result:Split/bytes,_:2>> = Result0,
-		    Result
-	    end;
-	Bits ->
-	    decode_binary(<<Result0/bits,Bits:6>>, T0)
+decode_binary(<<C1:8, Cs/bits>>, A) ->
+    case element(C1, ?DECODE_MAP) of
+        ws -> decode_binary(Cs, A);
+        B1 -> decode_binary(Cs, A, B1)
     end;
-decode_binary(Result, <<>>) ->
-    true = is_binary(Result),
-    Result.
+decode_binary(<<>>, A) ->
+    A.
+
+decode_binary(<<C2:8, Cs/bits>>, A, B1) ->
+    case element(C2, ?DECODE_MAP) of
+        ws -> decode_binary(Cs, A, B1);
+        B2 -> decode_binary(Cs, A, B1, B2)
+    end.
+
+decode_binary(<<C3:8, Cs/bits>>, A, B1, B2) ->
+    case element(C3, ?DECODE_MAP) of
+        ws -> decode_binary(Cs, A, B1, B2);
+        B3 -> decode_binary(Cs, A, B1, B2, B3)
+    end.
+
+decode_binary(<<C4:8, Cs/bits>>, A, B1, B2, B3) ->
+    case element(C4, ?DECODE_MAP) of
+        ws                -> decode_binary(Cs, A, B1, B2, B3);
+        eq when B3 =:= eq -> only_ws_binary(Cs, <<A/binary,B1:6,(B2 bsr 4):2>>);
+        eq                -> only_ws_binary(Cs, <<A/binary,B1:6,B2:6,(B3 bsr 2):4>>);
+        B4                -> decode_binary(Cs, <<A/binary,B1:6,B2:6,B3:6,B4:6>>)
+    end.
+
+only_ws_binary(<<>>, A) ->
+    A;
+only_ws_binary(<<C:8, Cs/bits>>, A) ->
+    case element(C, ?DECODE_MAP) of
+        ws -> only_ws_binary(Cs, A);
+        _ -> erlang:error(function_clause)
+    end.
 
 %% Skipping pad character if not at end of string. Also liberal about
 %% excess padding and skipping of other illegal (non-base64 alphabet)
@@ -328,16 +338,6 @@ strip_spaces([$\r|Cs], A) -> strip_spaces(Cs, A);
 strip_spaces([$\n|Cs], A) -> strip_spaces(Cs, A);
 strip_spaces([C|Cs], A) -> strip_spaces(Cs, [C | A]).
 
-strip_ws(<<$\t,T/binary>>) ->
-    strip_ws(T);
-strip_ws(<<$\n,T/binary>>) ->
-    strip_ws(T);
-strip_ws(<<$\r,T/binary>>) ->
-    strip_ws(T);
-strip_ws(<<$\s,T/binary>>) ->
-    strip_ws(T);
-strip_ws(T) -> T.
-
 %% Skipping pad character if not at end of string. Also liberal about
 %% excess padding and skipping of other illegal (non-base64 alphabet)
 %% characters. See section 3.3 of RFC4648
-- 
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