Merge pull request #1565 from mikpe/stdlib-base64-decode-speedup

base64:decode(List) optimized reimplementation

OTP-14624

1 files changed, 72 insertions, 36 deletions

diff --git a/lib/stdlib/src/base64.erl b/lib/stdlib/src/base64.erl
index 5885745fb1..c8cf6fdffe 100644
--- a/lib/stdlib/src/base64.erl
+++ b/lib/stdlib/src/base64.erl
@@ -113,9 +113,9 @@ encode_binary(Bin) ->
       Data :: ascii_binary().
 
 decode(Bin) when is_binary(Bin) ->
-    decode_binary(<<>>, Bin);
+    decode_binary(Bin, <<>>);
 decode(List) when is_list(List) ->
-    list_to_binary(decode_l(List)).
+    decode_list(List, <<>>).
 
 -spec mime_decode(Base64) -> Data when
       Base64 :: ascii_string() | ascii_binary(),
@@ -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)
@@ -262,6 +272,42 @@ mime_decode_binary_after_eq(Result0, <<>>, Eq) ->
             Result
     end.
 
+decode_list([C1 | Cs], A) ->
+    case element(C1, ?DECODE_MAP) of
+        ws -> decode_list(Cs, A);
+        B1 -> decode_list(Cs, A, B1)
+    end;
+decode_list([], A) ->
+    A.
+
+decode_list([C2 | Cs], A, B1) ->
+    case element(C2, ?DECODE_MAP) of
+        ws -> decode_list(Cs, A, B1);
+        B2 -> decode_list(Cs, A, B1, B2)
+    end.
+
+decode_list([C3 | Cs], A, B1, B2) ->
+    case element(C3, ?DECODE_MAP) of
+        ws -> decode_list(Cs, A, B1, B2);
+        B3 -> decode_list(Cs, A, B1, B2, B3)
+    end.
+
+decode_list([C4 | Cs], A, B1, B2, B3) ->
+    case element(C4, ?DECODE_MAP) of
+        ws                -> decode_list(Cs, A, B1, B2, B3);
+        eq when B3 =:= eq -> only_ws(Cs, <<A/binary,B1:6,(B2 bsr 4):2>>);
+        eq                -> only_ws(Cs, <<A/binary,B1:6,B2:6,(B3 bsr 2):4>>);
+        B4                -> decode_list(Cs, <<A/binary,B1:6,B2:6,B3:6,B4:6>>)
+    end.
+
+only_ws([], A) ->
+    A;
+only_ws([C | Cs], A) ->
+    case element(C, ?DECODE_MAP) of
+        ws -> only_ws(Cs, A);
+        _ -> erlang:error(function_clause)
+    end.
+
 decode([], A) -> A;
 decode([$=,$=,C2,C1|Cs], A) ->
     Bits2x6 = (b64d(C1) bsl 18) bor (b64d(C2) bsl 12),
@@ -292,16 +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