From f4c7a59d96b110f79cc0fcc16286ece770a166a3 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= Date: Tue, 19 Feb 2013 15:00:23 +0100 Subject: asn1_constructed_per: Optimize decoding of CHOICE Optimize the decoding of CHOICE. Most important is to inline decoding of the extension bit (if present) and decoding of the choice index to give the BEAM compiler more opportunities for optimization. We will also change the structure of the generated code. The current code uses a flattened case for both the root and extension alternatives: case Choice + NumRootChoices * Ext of %% Root alternatives. 0 - ...; : LastRootAlternative -> ...; %% Extension alternatives. LastRootAlternative+1 -> ...; : %% Unknown extension. _ -> ...; end We will instead generate nested cases: case Ext of 0 -> case Choice of %% Root alternatives. 0 - ...; : LastRootAlternative -> ... end; 1 -> %% Extension alternatives. case Choice of 0 -> ...; : LastExtensionAlternative -> ...; %% Unknown extension. _ -> ...; end end Nested cases should be slightly faster. For decoding of the extensions, it also makes it possible to hoist the decoding of the open type up from each case to before the case switching on the extension index, thus reducing the size of the generated code. We will also do another change to the structure. Currently, the big flat clase is wrapped in code that repackages the return values: {Alt,{Value,RemainingEncodedData}} = case Choice + NumRootChoices * Ext of : end, {{Value,Alt},RemainingEncodedData}. We still need to do the repackaging, but we can push it down to the case arm for decoding each alternative. In many cases, that will give the BEAM compiler the opportunity to avoid building the temporary tuples. --- lib/asn1/src/asn1ct_constructed_per.erl | 160 +++++++++++++++++++++++--------- 1 file changed, 116 insertions(+), 44 deletions(-) (limited to 'lib/asn1/src/asn1ct_constructed_per.erl') diff --git a/lib/asn1/src/asn1ct_constructed_per.erl b/lib/asn1/src/asn1ct_constructed_per.erl index 7fc904ec16..c3067e53be 100644 --- a/lib/asn1/src/asn1ct_constructed_per.erl +++ b/lib/asn1/src/asn1ct_constructed_per.erl @@ -1322,8 +1322,7 @@ gen_dec_component_no_val({ext,_,_},mandatory) -> emit({"asn1_NOVALUE"}). -gen_dec_choice_line(Erule, TopType, Comp, Pos, Ext) -> - Pre = gen_dec_line_open_type(Erule, Ext, Pos), +gen_dec_choice_line(Erule, TopType, Comp, Pre) -> Imm0 = gen_dec_line_imm(Erule, TopType, Comp, false, Pre), Init = {ignore,fun(_) -> {[],[]} end}, Imm = [{group,[Init|Imm0]}], @@ -1638,62 +1637,135 @@ gen_enc_choice2(Erule, TopType, [H|T], Pos, Sep0, Ext) -> gen_enc_choice2(Erule, TopType, T, Pos+1, Sep, Ext); gen_enc_choice2(_, _, [], _, _, _) -> ok. -gen_dec_choice(Erule,TopType,CompList,{ext,Pos,NumExt}) -> - emit(["{Ext,",{curr,bytes},"} = ", - {call,Erule,getbit,["Bytes"]},com,nl]), +%% Generate the code for CHOICE. If the CHOICE is extensible, +%% the structure of the generated code is as follows: +%% +%% case Bytes of +%% <<0:1,Bytes1/bitstring>> -> +%% Choice = +%% case Choice of +%% 0 -> ; +%% : +%% LastRootChoice -> +%% end; +%% <<1:1,Bytes1/bitstring>> -> +%% Choice = +%% TmpVal = +%% case Choice of +%% 0 -> ; +%% : +%% LastExtension -> ; +%% _ -> +%% end +%% end +%% +%% The return value from the generated function always looks like: +%% {{ChoiceTag,Value},RemainingBuffer} +%% where ChoiceTag will be 'asn1_ExtAlt' for an unknown extension. +%% +%% If the CHOICE is not extensible, the top-level case is omitted +%% and only the code in the first case arm is generated. + +gen_dec_choice(Erule, TopType, CompList, {ext,_,_}=Ext) -> + {RootList,ExtList} = split_complist(CompList), + emit(["case Bytes of",nl]), + case RootList of + [] -> + ok; + [_|_] -> + emit(["<<0:1,Bytes1/bitstring>> ->",nl]), + asn1ct_name:new(bytes), + gen_dec_choice1(Erule, TopType, RootList, noext), + emit([";",nl,nl]) + end, + emit(["<<1:1,Bytes1/bitstring>> ->",nl]), + asn1ct_name:clear(), + asn1ct_name:new(bytes), asn1ct_name:new(bytes), - gen_dec_choice1(Erule,TopType,CompList,{ext,Pos,NumExt}); -gen_dec_choice(Erule,TopType,CompList,noext) -> - gen_dec_choice1(Erule,TopType,CompList,noext). - -gen_dec_choice1(Erule,TopType,CompList,noext) -> - emit(["{Choice,",{curr,bytes}, - "} = ",{call,Erule,getchoice, - [{prev,bytes},length(CompList),"0"]},com,nl, - "{Cname,{Val,NewBytes}} = case Choice of",nl]), - gen_dec_choice2(Erule,TopType,CompList,noext), - emit({nl,"end,",nl}), - emit({nl,"{{Cname,Val},NewBytes}"}); -gen_dec_choice1(Erule,TopType,{RootList,ExtList},Ext) -> - NewList = RootList ++ ExtList, - gen_dec_choice1(Erule,TopType, NewList, Ext); -gen_dec_choice1(Erule,TopType,{RootList,ExtList,RootList2},Ext) -> - NewList = RootList ++ RootList2 ++ ExtList, - gen_dec_choice1(Erule,TopType, NewList, Ext); -gen_dec_choice1(Erule,TopType,CompList,{ext,ExtPos,ExtNum}) -> - emit(["{Choice,",{curr,bytes},"} = ", - {call,Erule,getchoice, - [{prev,bytes},length(CompList)-ExtNum,"Ext"]},com,nl]), - emit({"{Cname,{Val,NewBytes}} = case Choice + Ext*",ExtPos-1," of",nl}), - gen_dec_choice2(Erule,TopType,CompList,{ext,ExtPos,ExtNum}), + gen_dec_choice1(Erule, TopType, ExtList, Ext), + emit([nl,"end"]); +gen_dec_choice(Erule, TopType, CompList, noext) -> + gen_dec_choice1(Erule, TopType, CompList, noext). + +split_complist({Root1,Ext,Root2}) -> + {Root1++Root2,Ext}; +split_complist({_,_}=CompList) -> + CompList. + +gen_dec_choice1(Erule, TopType, CompList, noext=Ext) -> + emit_getchoice(Erule, CompList, Ext), + emit(["case Choice of",nl]), + Pre = {safe,fun(St) -> + {asn1ct_gen:mk_var(asn1ct_name:curr(bytes)), + fun() -> St end} + end}, + gen_dec_choice2(Erule, TopType, CompList, Pre), + emit([nl,"end"]); +gen_dec_choice1(Erule, TopType, CompList, {ext,_,_}=Ext) -> + emit_getchoice(Erule, CompList, Ext), Imm = asn1ct_imm:per_dec_open_type(is_aligned(Erule)), + emit(["begin",nl]), BytesVar = asn1ct_gen:mk_var(asn1ct_name:curr(bytes)), - emit([";",nl, - "_ ->",nl]), - {TmpTerm,TmpBuf} = asn1ct_imm:dec_slim_cg(Imm, BytesVar), - emit([com,nl, - "{asn1_ExtAlt,{",TmpTerm,com,TmpBuf,"}}",nl, - "end,",nl,nl, - "{{Cname,Val},NewBytes}"]). - + {Dst,DstBuf} = asn1ct_imm:dec_slim_cg(Imm, BytesVar), + emit([nl, + "end,",nl, + "case Choice of",nl]), + Pre = {safe,fun(St) -> + emit(["{TmpVal,_} = "]), + {Dst, + fun() -> + emit([",",nl, + "{TmpVal,",DstBuf,"}"]), + St + end} + end}, + gen_dec_choice2(Erule, TopType, CompList, Pre), + case CompList of + [] -> ok; + [_|_] -> emit([";",nl]) + end, + emit(["_ ->",nl, + "{{asn1_ExtAlt,",Dst,"},",DstBuf,"}",nl, + "end"]). + +emit_getchoice(Erule, CompList, Ext) -> + Al = is_aligned(Erule), + Imm = case {Ext,CompList} of + {noext,[_]} -> + {value,0}; + {noext,_} -> + asn1ct_imm:per_dec_constrained(0, length(CompList)-1, Al); + {{ext,_,_},_} -> + asn1ct_imm:per_dec_normally_small_number(Al) + end, + emit(["{Choice,",{curr,bytes},"} = ",nl]), + BytesVar = asn1ct_gen:mk_var(asn1ct_name:prev(bytes)), + asn1ct_imm:dec_code_gen(Imm, BytesVar), + emit([com,nl]). gen_dec_choice2(Erule,TopType,L,Ext) -> gen_dec_choice2(Erule, TopType, L, 0, [], Ext). -gen_dec_choice2(Erule, TopType, [H0|T], Pos, Sep0, Ext) -> +gen_dec_choice2(Erule, TopType, [H0|T], Pos, Sep0, Pre) -> #'ComponentType'{name=Cname,typespec=Type} = H0, H = H0#'ComponentType'{prop=mandatory}, + emit([Sep0,Pos," ->",nl]), case Type#type.def of #'ObjectClassFieldType'{type={typefield,_}} -> - emit([Sep0,Pos," ->",nl]), - gen_dec_choice_line(Erule, TopType, H, Pos+1, Ext); + emit("{Cname,{Val,NewBytes}} = begin\n"), + gen_dec_choice_line(Erule, TopType, H, Pre), + emit([nl, + "end,",nl, + "{{Cname,Val},NewBytes}"]); _ -> - emit([Sep0,Pos," -> {",{asis,Cname},",",nl]), - gen_dec_choice_line(Erule, TopType, H, Pos+1, Ext), - emit("}") + emit("{Val,NewBytes} = begin\n"), + gen_dec_choice_line(Erule, TopType, H, Pre), + emit([nl, + "end,",nl, + "{{",{asis,Cname},",Val},NewBytes}"]) end, Sep = [";",nl], - gen_dec_choice2(Erule, TopType, T, Pos+1, Sep, Ext); + gen_dec_choice2(Erule, TopType, T, Pos+1, Sep, Pre); gen_dec_choice2(_, _, [], _, _, _) -> ok. indent(N) -> -- cgit v1.2.3