PER: Optimize encoding of character strings with simple ranges

The encoder for the following type would generate a dialyzer warning:

  Ns ::= NumericString (FROM ("0"|"1"|"2"|"3"|"4"|"5"|"6"|"7"|"8"|"9"))

Optimize this case to make it slightly faster as well as eliminate
the dialyzer warning.

2 files changed, 31 insertions, 8 deletions

diff --git a/lib/asn1/src/asn1ct_imm.erl b/lib/asn1/src/asn1ct_imm.erl
index fde39c674e..321d32ef17 100644
--- a/lib/asn1/src/asn1ct_imm.erl
+++ b/lib/asn1/src/asn1ct_imm.erl
@@ -265,10 +265,6 @@ per_enc_k_m_string(Val0, StringType, Constraint, Aligned) ->
     SzConstraint = effective_constraint(bitstring, Constraint),
     Unit = string_num_bits(StringType, Constraint, Aligned),
     Chars0 = char_tab(Constraint, StringType, Unit),
-    Args = case enc_char_tab(Chars0) of
-	       notab -> [Val,Unit];
-	       Chars -> [Val,Unit,Chars]
-	   end,
     Enc = case Unit of
 	      16 ->
 		  {call,per_common,encode_chars_16bit,[Val],Bin};
@@ -277,7 +273,15 @@ per_enc_k_m_string(Val0, StringType, Constraint, Aligned) ->
 	      8 ->
 		  {call,erlang,list_to_binary,[Val],Bin};
 	      _ ->
-		  {call,per_common,encode_chars,Args,Bin}
+		  case enc_char_tab(Chars0) of
+		      notab ->
+			  {call,per_common,encode_chars,[Val,Unit],Bin};
+		      {tab,Tab} ->
+			  {call,per_common,encode_chars,[Val,Unit,Tab],Bin};
+		      {compact_map,Map} ->
+			  {call,per_common,encode_chars_compact_map,
+			   [Val,Unit,Map],Bin}
+		  end
 	  end,
     case Unit of
 	8 ->
@@ -1303,9 +1307,15 @@ prepend_to_cond_1([Check|T], Code) ->
 enc_char_tab(notab) ->
     notab;
 enc_char_tab(Tab0) ->
-    Tab = tuple_to_list(Tab0),
-    First = hd(Tab),
-    {First-1,list_to_tuple(enc_char_tab_1(Tab, First, 0))}.
+    Tab1 = tuple_to_list(Tab0),
+    First = hd(Tab1),
+    Tab = enc_char_tab_1(Tab1, First, 0),
+    case lists:member(ill, Tab) of
+	false ->
+	    {compact_map,{First,tuple_size(Tab0)}};
+	true ->
+	    {tab,{First-1,list_to_tuple(Tab)}}
+    end.
 
 enc_char_tab_1([H|T], H, I) ->
     [I|enc_char_tab_1(T, H+1, I+1)];
diff --git a/lib/asn1/src/asn1rtt_per_common.erl b/lib/asn1/src/asn1rtt_per_common.erl
index 71fec411a0..0290c75a28 100644
--- a/lib/asn1/src/asn1rtt_per_common.erl
+++ b/lib/asn1/src/asn1rtt_per_common.erl
@@ -30,6 +30,7 @@
 	 decode_big_chars/2,
 	 decode_oid/1,decode_relative_oid/1,
 	 encode_chars/2,encode_chars/3,
+	 encode_chars_compact_map/3,
 	 encode_chars_16bit/1,encode_big_chars/1,
 	 encode_fragmented/2,
 	 encode_oid/1,encode_relative_oid/1,
@@ -108,6 +109,9 @@ encode_chars(Val, NumBits) ->
 encode_chars(Val, NumBits, {Lb,Tab}) ->
     << <<(enc_char(C, Lb, Tab)):NumBits>> || C <- Val >>.
 
+encode_chars_compact_map(Val, NumBits, {Lb,Limit}) ->
+    << <<(enc_char_cm(C, Lb, Limit)):NumBits>> || C <- Val >>.
+
 encode_chars_16bit(Val) ->
     L = [case C of
 	     {0,0,A,B} -> [A,B];
@@ -383,6 +387,15 @@ enc_char(C0, Lb, Tab) ->
 	    illegal_char_error()
     end.
 
+enc_char_cm(C0, Lb, Limit) ->
+    C = C0 - Lb,
+    if
+	0 =< C, C < Limit ->
+	    C;
+	true ->
+	    illegal_char_error()
+    end.
+
 illegal_char_error() ->
     error({error,{asn1,"value forbidden by FROM constraint"}}).