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<?xml version="1.0" encoding="iso-8859-1" ?>
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<!DOCTYPE chapter SYSTEM "chapter.dtd">
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<holder>Ericsson AB, All Rights Reserved</holder>
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The contents of this file are subject to the Erlang Public License,
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Version 1.1, (the "License"); you may not use this file except in
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compliance with the License. You should have received a copy of the
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Erlang Public License along with this software. If not, it can be
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retrieved online at http://www.erlang.org/.
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Software distributed under the License is distributed on an "AS IS"
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basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
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the License for the specific language governing rights and limitations
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The Initial Developer of the Original Code is Ericsson AB.
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<title>Specialized Decodes</title>
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<prepared>EAB/UAB/UKH/KD Bertil Karlsson</prepared>
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<date>2003-04-24</date>
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<file>asn1_spec.sgml</file>
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<marker id="SpecializedDecodes"></marker>
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<p>When performance is of highest priority and one is interested in
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a limited part of the ASN.1 encoded message, before one decide what
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to do with the rest of it, one may want to decode only this small
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part. The situation may be a server that has to decide to which
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addressee it will send a message. The addressee may be interested in
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the entire message, but the server may be a bottleneck that one want
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to spare any unnecessary load. Instead of making two <em>complete decodes</em> (the normal case of decode), one in the server and one
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in the addressee, it is only necessary to make one <em>specialized decode</em>(in the server) and another complete decode(in the
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addressee). The following specialized decodes <em>exclusive decode</em> and <em>selected decode</em> support to solve this and
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<p>So far this functionality is only provided when using the
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optimized BER_BIN version, that is when compiling with the
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options <c>ber_bin</c> and <c>optimize</c>. It does also work
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using the <c>driver</c> option. We have no intent to make this
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available on the default BER version, but maybe in the PER_BIN
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version (<c>per_bin</c>).
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<title>Exclusive Decode</title>
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<p>The basic idea with exclusive
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decode is that you specify which parts of the message you want to
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exclude from being decoded. These parts remain encoded and are
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returned in the value structure as binaries. They may be decoded
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in turn by passing them to a certain <c>decode_part/2</c>
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function. The performance gain is high when the message is large
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and you can do an exclusive decode and later on one or several
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decodes of the parts or a second complete decode instead of two or
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more complete decodes.
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<title>How To Make It Work</title>
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<p>In order to make exclusive decode work you have to do the
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<list type="bulleted">
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<item>First,decide the name of the function for the exclusive
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<item>Second, write instructions that must consist of the name
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of the exclusive decode function, the name of the ASN.1
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specification and a notation that tells which parts of the
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message structure will be excluded from decode. These
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instructions shall be included in a configuration
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<item>Third, compile with the additional option
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<c>asn1config</c>. The compiler searches for a configuration
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file with the same name as the ASN.1 spec but with the
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extension .asn1config. This configuration file is not the same
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as used for compilation of a set of files. See section
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<seealso marker="#UndecodedPart">Writing an Exclusive Decode Instruction.</seealso></item>
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<title>User Interface</title>
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<p>The run-time user interface for exclusive decode consists of
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two different functions. First, the function for an exclusive
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decode, whose name the user decides in the configuration
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file. Second, the compiler generates a <c>decode_part/2</c>
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function when exclusive decode is chosen. This function decodes
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the parts that were left undecoded during the exclusive
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decode. Both functions are described below.
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<p>If the exclusive decode function has for example got the name
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<c>decode_exclusive</c> and an ASN.1 encoded message
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<c>Bin</c> shall be exclusive decoded, the call is:</p>
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{ok,Excl_Message} = 'MyModule':decode_exclusive(Bin) </pre>
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<marker id="UndecodedPart"></marker>
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<p>The result <c>Excl_Message</c> has the same structure as an
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complete decode would have, except for the parts of the top-type
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that were not decoded. The undecoded parts will be on their place
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in the structure on the format <c>{Type_Key,Undecoded_Value}</c>.
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<p>Each undecoded part that shall be decoded must be fed into the <c>decode_part/2</c> function,like:</p>
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{ok,Part_Message} = 'MyModule':decode_part(Type_Key,Undecoded_Value) </pre>
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<marker id="Exclusive Instruction"></marker>
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<title>Writing an Exclusive Decode Instruction</title>
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<p>This instruction is written in the configuration file on the
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Exclusive_Decode_Instruction = {exclusive_decode,{Module_Name,Decode_Instructions}}.
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Decode_Instructions = [Decode_Instruction]+
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Decode_Instruction = {Exclusive_Decode_Function_Name,Type_List}
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Exclusive_Decode_Function_Name = atom()
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Type_List = [Top_Type,Element_List]
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Element_List = [Element]+
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Element = {Name,parts} |
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<p>Observe that the instruction must be a valid Erlang term ended
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<p>In the <c>Type_List</c> the "path" from the top type to each
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undecoded sub-components is described. The top type of the path is
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an atom, the name of it. The action on each component/type that
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follows will be described by one of <c>{Name,parts}, {Name,undecoded}, {Name,Element_List}</c></p>
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<p>The use and effect of the actions are:
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<list type="bulleted">
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<item><c>{Name,undecoded}</c> Tells that the element will be
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left undecoded during the exclusive decode. The type of Name may
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be any ASN.1 type. The value of element Name will be returned as a
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tuple,as mentioned <seealso marker="#UndecodedPart">above</seealso>, in the value structure of the top type.</item>
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<item><c>{Name,parts}</c> The type of Name may be one of
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SEQUENCE OF or SET OF. The action implies that the different
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components of Name will be left undecoded. The value of Name
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will be returned as a tuple, as <seealso marker="#UndecodedPart">above </seealso>, where the second element is a list of
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binaries. That is because the representation of a SEQUENCE OF/
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SET OF in Erlang is a list of its internal type. Any of the
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elements of this list or the entire list can be decoded by the
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<c>decode_part</c> function.</item>
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<item><c>{Name,Element_List}</c>This action is used when one or
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more of the sub-types of Name will be exclusive decoded.</item>
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<p>Name in the actions above may be a component name of a
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SEQUENCE or a SET or a name of an alternative in a CHOICE.
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<title>Example</title>
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<p>In the examples below we use the definitions from the following ASN.1 spec:</p>
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<marker id="Asn1spec"></marker>
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<codeinclude file="Seq.asn" tag="" type="none"></codeinclude>
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<p>If <c>Button</c> is a top type and we want to exclude
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component <c>number</c> from decode the Type_List in the
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instruction in the configuration file will be
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<c>['Button',[{number,undecoded}]]</c>. If we call the decode
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function <c>decode_Button_exclusive</c> the Decode_Instruction
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<c>{decode_Button_exclusive,['Button',[{number,undecoded}]]}</c>.
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<p>We also have another top type <c>Window</c> whose sub
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component actions in type <c>Status</c> and the parts of component
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<c>buttonList</c> shall be left undecoded. For this type we name
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the function <c>decode__Window_exclusive</c>. The whole
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Exclusive_Decode_Instruction configuration is as follows: </p>
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<codeinclude file="Seq.asn1config" tag="" type="none"></codeinclude>
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<image file="exclusive_Win_But">
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<icaption>Figure symbolizes the bytes of a Window:status message. The components buttonList and actions are excluded from decode. Only state and enabled are decoded when decode__Window_exclusive is called. </icaption>
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<p>Compiling GUI.asn including the configuration file is done like:</p>
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unix> erlc -bber_bin +optimize +asn1config GUI.asn
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erlang> asn1ct:compile('GUI',[ber_bin,optimize,asn1config]). </pre>
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<p>The module can be used like:</p>
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1> Button_Msg = {'Button',123,true}.
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2> {ok,Button_Bytes} = 'GUI':encode('Button',Button_Msg).
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{ok,[<<48>>,
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[<<128>>,
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[<<129>>,
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3> {ok,Exclusive_Msg_Button} = 'GUI':decode_Button_exclusive(list_to_binary(Button_Bytes)).
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{ok,{'Button',{'Button_number',<<28,1,123>>},
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4> 'GUI':decode_part('Button_number',<<128,1,123>>).
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{'Window',{status,{'Status',35,
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{possibleActions,[{'Action',16,{'Button',17,true}}]}}}}.
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{'Window',{status,{'Status',35,
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{possibleActions,[{'Action',16,{'Button',17,true}}]}}}}
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6> {ok,Window_Bytes}='GUI':encode('Window',Window_Msg).
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{ok,[<<161>>,
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[<<128>>, ...
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8> {ok,{status,{'Status',Int,{Type_Key_SeqOf,Val_SEQOF},
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BoolOpt,{Type_Key_Choice,Val_Choice}}}}=
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'GUI':decode_Window_status_exclusive(list_to_binary(Window_Bytes)).
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{ok,{status,{'Status',35,
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{'Status_buttonList',[<<48,6,128,1,3,129,1,255>>,
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<<48,6,128,1,4,129,1,0>>,
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<<48,6,128,1,5,129,1,255>>,
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<<48,6,128,1,6,129,1,255>>,
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<<48,6,128,1,7,129,1,0>>,
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<<48,6,128,1,8,129,1,255>>,
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<<48,6,128,1,9,129,1,255>>,
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<<48,6,128,1,10,129,1,0>>,
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<<48,6,128,1,11,129,1,255>>,
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<<48,6,128,1,12,129,1,255>>,
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<<48,6,128,1,13,129,1,0>>,
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<<48,6,128,1,14,129,1,255>>]},
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<<163,21,160,19,48,17,2,1,16,160,12,172,10,171,8,48,6,128,1,...>>}}}}
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10> 'GUI':decode_part(Type_Key_SeqOf,Val_SEQOF).
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{ok,[{'Button',3,true},
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11> 'GUI':decode_part(Type_Key_SeqOf,hd(Val_SEQOF)).
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{ok,{'Button',3,true}}
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12> 'GUI':decode_part(Type_Key_Choice,Val_Choice).
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{ok,{possibleActions,[{'Action',16,{'Button',17,true}}]}}
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<title>Selective Decode</title>
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<p>This specialized decode decodes one single subtype of a
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constructed value. It is the fastest method to extract one sub
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value. The typical use of this decode is when one want to
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inspect, for instance a version number,to be able to decide what
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to do with the entire value. The result is returned as
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<c>{ok,Value}</c> or <c>{error,Reason}</c>.
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<title>How To Make It Work</title>
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<p>The following steps are necessary:
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<list type="bulleted">
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<item>Write instructions in the configuration
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file. Including the name of a user function, the name of the ASN.1
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specification and a notation that tells which part of the type
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will be decoded. </item>
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<item>Compile with the additional option
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<c>asn1config</c>. The compiler searches for a configuration file
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with the same name as the ASN.1 spec but with the extension
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.asn1config. In the same file you can provide configuration specs
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for exclusive decode as well. The generated Erlang module has the
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usual functionality for encode/decode preserved and the
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specialized decode functionality added. </item>
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<title>User Interface</title>
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<p>The only new user interface function is the one provided by the
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user in the configuration file. You can invoke that function by
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the <c>ModuleName:FunctionName</c> notation.
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<p>So, if you have the following spec
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<c>{selective_decode,{'ModuleName',[{selected_decode_Window,TypeList}]}}</c>
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in the con-fig file, you do the selective decode by
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<c>{ok,Result}='ModuleName':selected_decode_Window(EncodedBinary).</c></p>
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<marker id="Selective Instruction"></marker>
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<title>Writing a Selective Decode Instruction</title>
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<p>It is possible to describe one or many selective decode
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functions in a configuration file, you have to use the following
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Selective_Decode_Instruction = {selective_decode,{Module_Name,Decode_Instructions}}.
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Decode_Instructions = [Decode_Instruction]+
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Decode_Instruction = {Selective_Decode_Function_Name,Type_List}
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Selective_Decode_Function_Name = atom()
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Type_List = [Top_Type|Element_List]
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Element_List = Name|List_Selector
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List_Selector = [integer()] </pre>
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<p>Observe that the instruction must be a valid Erlang term ended
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<p>The <c>Module_Name</c> is the same as the name of the ASN.1
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spec, but without the extension. A <c>Decode_Instruction</c> is
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a tuple with your chosen function name and the components from
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the top type that leads to the single type you want to
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decode. Notice that you have to choose a name of your function
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that will not be the same as any of the generated functions. The
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first element of the <c>Type_List</c> is the top type of the
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encoded message. In the <c>Element_List</c> it is followed by
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each of the component names that leads to selected type. Each of
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the names in the <c>Element_List</c> must be constructed types
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except the last name, which can be any type.
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<p>The List_Selector makes it possible to choose one of the
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encoded components in a SEQUENCE OF/ SET OF. It is also possible
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to go further in that component and pick a sub type of that to
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decode. So in the <c>Type_List</c>: <c>['Window',status,buttonList,[1],number]</c> the
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component <c>buttonList</c> has to be a SEQUENCE OF or SET OF type. In
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this example component <c>number</c> of the first of the encoded
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elements in the SEQUENCE OF <c>buttonList</c> is selected. This apply on
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the ASN.1 spec <seealso marker="#Asn1spec">above</seealso>.
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<title>Another Example</title>
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<p>In this example we use the same ASN.1 spec as <seealso marker="#Asn1spec">above</seealso>. A valid selective decode
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[{selected_decode_Window1,
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['Window',status,buttonList,
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{selected_decode_Action,
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['Action',handle,number]},
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{selected_decode_Window2,
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<p>The first <c>Decode_Instruction</c>,
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<c>{selected_decode_Window1,['Window',status,buttonList,[1],number]}</c>
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is commented in the previous section. The instruction
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<c>{selected_decode_Action,['Action',handle,number]}</c> picks
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the component <c>number</c> in the <c>handle</c> component of the type
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<c>Action</c>. If we have the value <c>ValAction = {'Action',17,{'Button',4711,false}}</c> the internal value 4711
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should be picked by <c>selected_decode_Action</c>. In an Erlang
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terminal it looks like:</p>
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ValAction = {'Action',17,{'Button',4711,false}}.
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{'Action',17,{'Button',4711,false}}
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7> {ok,Bytes}='GUI':encode('Action',ValAction).
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8> BinBytes = list_to_binary(Bytes).
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<<48,18,2,1,17,160,13,172,11,171,9,48,7,128,2,18,103,129,1,0>>
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9> 'GUI':selected_decode_Action(BinBytes).
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<p>The third instruction,
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<c>['Window',status,actions,possibleActions,[1],handle,number]</c>,
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which is a little more complicated,</p>
432
<list type="bulleted">
433
<item>starts with type <em>Window</em>. </item>
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<item>Picks component <em>status</em> of <c>Window</c> that is
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of type <c>Status</c>.</item>
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<item>Then takes component <em>actions</em> of type
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<c>Status</c>.</item>
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<item>Then <em>possibleActions</em> of the internal defined
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<item>Thereafter it goes into the first component of the
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SEQUENCE OF by <em>[1]</em>. That component is of type
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<c>Action</c>.</item>
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<item>The instruction next picks component
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<em>handle</em>.</item>
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<item>And finally component <em>number</em> of the type
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<c>Button</c>.</item>
448
<p>The following figures shows which components are in the
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<c>['Window',status,actions,possibleActions,[1],handle,number]</c>. And
451
which part of a message that will be decoded by
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selected_decode_Window2.
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<image file="selective_TypeList">
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<icaption>The elements specified in the config file for selective decode of a sub-value in a Window message</icaption>
459
<image file="selective_Window2">
460
<icaption>Figure symbolizes the bytes of a Window:status message. Only the marked element is decoded when selected_decode_Window2 is called. </icaption>
462
<p>With the following example you can examine that both
463
<c>selected_decode_Window2</c> and
464
<c>selected_decode_Window1</c> decodes the intended sub-value
465
of the value <c>Val</c></p>
467
1> Val = {'Window',{status,{'Status',12,
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{'Button',16,false}],
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{possibleActions,[{'Action',17,{'Button',18,false}},
474
{'Action',19,{'Button',20,true}},
475
{'Action',21,{'Button',22,false}}]}}}}
476
2> {ok,Bytes}='GUI':encode('Window',Val).
478
3> Bin = list_to_binary(Bytes).
479
<<161,101,128,1,12,161,32,48,6,128,1,13,129,1,255,48,6,128,1,14,129,1,0,48,6,128,1,15,129,...>>
480
4> 'GUI':selected_decode_Window1(Bin).
482
5> 'GUI':selected_decode_Window2(Bin).
484
<p>Observe that the value feed into the selective decode
485
functions must be a binary.
491
<title>Performance</title>
492
<p>To give an indication on the possible performance gain using
493
the specialized decodes, some measures have been performed. The
494
relative figures in the outcome between selective, exclusive and
495
complete decode (the normal case) depends on the structure of
496
the type, the size of the message and on what level the
497
selective and exclusive decodes are specified.
501
<title>ASN.1 Specifications, Messages and Configuration</title>
502
<p>The specs <seealso marker="#Asn1spec">GUI</seealso> and
503
<url href="http://www.itu.int/ITU-T/asn1/database/itu-t/h/h248/2002/MEDIA-GATEWAY-CONTROL.html">MEDIA-GATEWAY-CONTROL</url>
504
was used in the test.
506
<p>For the GUI spec the configuration looked like:</p>
510
[{selected_decode_Window1,
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{selected_decode_Window2,
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[{decode_Window_status_exclusive,
528
{actions,undecoded}]}]]}]}}.
530
<p>The MEDIA-GATEWAY-CONTROL configuration was:</p>
533
{'MEDIA-GATEWAY-CONTROL',
534
[{decode_MegacoMessage_exclusive,
536
[{authHeader,undecoded},
539
{messageBody,undecoded}]}]]}]}}.
541
{'MEDIA-GATEWAY-CONTROL',
542
[{decode_MegacoMessage_selective,
543
['MegacoMessage',mess,version]}]}}.
545
<p>The corresponding values were:</p>
547
{'Window',{status,{'Status',12,
559
{'Button',16,false}],
562
[{'Action',17,{'Button',18,false}},
563
{'Action',19,{'Button',20,true}},
564
{'Action',21,{'Button',22,false}},
565
{'Action',17,{'Button',18,false}},
566
{'Action',19,{'Button',20,true}},
567
{'Action',21,{'Button',22,false}},
568
{'Action',17,{'Button',18,false}},
569
{'Action',19,{'Button',20,true}},
570
{'Action',21,{'Button',22,false}},
571
{'Action',17,{'Button',18,false}},
572
{'Action',19,{'Button',20,true}},
573
{'Action',21,{'Button',22,false}},
574
{'Action',17,{'Button',18,false}},
575
{'Action',19,{'Button',20,true}},
576
{'Action',21,{'Button',22,false}},
577
{'Action',17,{'Button',18,false}},
578
{'Action',19,{'Button',20,true}},
579
{'Action',21,{'Button',22,false}}]}}}}
582
{'MegacoMessage',asn1_NOVALUE,
585
{'IP4Address',[125,125,125,111],55555}},
588
{'TransactionReply',50007,asn1_NOVALUE,
590
[{'ActionReply',0,asn1_NOVALUE,asn1_NOVALUE,
591
[{auditValueReply,{auditResult,{'AuditResult',
592
{'TerminationID',[],[255,255,255]},
594
{'MediaDescriptor',asn1_NOVALUE,
596
[{'StreamDescriptor',1,
598
{'LocalControlDescriptor',
606
{'LocalRemoteDescriptor',
613
[[73,78,32,73,80,52,32,49,50,53,46,49,
614
50,53,46,49,50,53,46,49,49,49]],
618
[[97,117,100,105,111,32,49,49,49,49,32,
619
82,84,80,47,65,86,80,32,32,52]],
623
[[112,116,105,109,101,58,51,48]],
625
{'LocalRemoteDescriptor',
632
[[73,78,32,73,80,52,32,49,50,52,46,49,50,
633
52,46,49,50,52,46,50,50,50]],
637
[[97,117,100,105,111,32,50,50,50,50,32,82,
638
84,80,47,65,86,80,32,32,52]],
642
[[112,116,105,109,101,58,51,48]],
643
asn1_NOVALUE}]]}}}]}}},
645
[{'PackagesItem',[0,11],1},
646
{'PackagesItem',[0,11],1}]},
647
{statisticsDescriptor,
648
[{'StatisticsParameter',[0,12,0,4],[[49,50,48,48]]},
649
{'StatisticsParameter',[0,11,0,2],[[54,50,51,48,48]]},
650
{'StatisticsParameter',[0,12,0,5],[[55,48,48]]},
651
{'StatisticsParameter',[0,11,0,3],[[52,53,49,48,48]]},
652
{'StatisticsParameter',[0,12,0,6],[[48,46,50]]},
653
{'StatisticsParameter',[0,12,0,7],[[50,48]]},
654
{'StatisticsParameter',[0,12,0,8],[[52,48]]}]}]}}}]}]}}}]}}}
656
<p>The size of the encoded values was 458 bytes for GUI and 464
657
bytes for MEDIA-GATEWAY-CONTROL.
662
<title>Results</title>
663
<p>The ASN.1 specs in the test are compiled with the options
664
<c>ber_bin, optimize, driver</c> and <c>asn1config</c>. If the
665
<c>driver</c> option had been omitted there should have been
666
higher values for <c>decode</c> and <c>decode_part</c>.
668
<p>The test program runs 10000 decodes on the value, resulting
669
in a printout with the elapsed time in microseconds for the
670
total number of decodes.
674
<cell align="left" valign="top"><em>Function</em></cell>
675
<cell align="left" valign="top"><em>Time</em>(microseconds)</cell>
676
<cell align="left" valign="top"><em>Kind of Decode</em></cell>
677
<cell align="left" valign="top"><em>ASN.1 spec</em></cell>
678
<cell align="left" valign="top"><em>% of time vs. complete decode</em></cell>
681
<cell align="left" valign="middle"><c>decode_MegacoMessage_selective/1</c></cell>
682
<cell align="left" valign="middle"><c>374045</c></cell>
683
<cell align="left" valign="middle"><c>selective</c></cell>
684
<cell align="left" valign="middle"><c>MEDIA-GATEWAY-CONTROL</c></cell>
685
<cell align="left" valign="middle"><em>8.3</em></cell>
688
<cell align="left" valign="middle"><c>decode_MegacoMessage_exclusive/1</c></cell>
689
<cell align="left" valign="middle"><c>621107</c></cell>
690
<cell align="left" valign="middle"><c>exclusive</c></cell>
691
<cell align="left" valign="middle"><c>MEDIA-GATEWAY-CONTROL</c></cell>
692
<cell align="left" valign="middle"><em>13.8</em></cell>
695
<cell align="left" valign="middle"><c>decode/2</c></cell>
696
<cell align="left" valign="middle"><c>4507457</c></cell>
697
<cell align="left" valign="middle"><c>complete</c></cell>
698
<cell align="left" valign="middle"><c>MEDIA-GATEWAY-CONTROL</c></cell>
699
<cell align="left" valign="middle"><em>100</em></cell>
702
<cell align="left" valign="middle"><c>selected_decode_Window1/1</c></cell>
703
<cell align="left" valign="middle"><c>449585</c></cell>
704
<cell align="left" valign="middle"><c>selective</c></cell>
705
<cell align="left" valign="middle"><c>GUI</c></cell>
706
<cell align="left" valign="middle"><em>7.6</em></cell>
709
<cell align="left" valign="middle"><c>selected_decode_Window2/1</c></cell>
710
<cell align="left" valign="middle"><c>890666</c></cell>
711
<cell align="left" valign="middle"><c>selective</c></cell>
712
<cell align="left" valign="middle"><c>GUI</c></cell>
713
<cell align="left" valign="middle"><em>15.1</em></cell>
716
<cell align="left" valign="middle"><c>decode_Window_status_exclusive/1</c></cell>
717
<cell align="left" valign="middle"><c>1251878</c></cell>
718
<cell align="left" valign="middle"><c>exclusive</c></cell>
719
<cell align="left" valign="middle"><c>GUI</c></cell>
720
<cell align="left" valign="middle"><em>21.3</em></cell>
723
<cell align="left" valign="middle"><c>decode/2</c></cell>
724
<cell align="left" valign="middle"><c>5889197</c></cell>
725
<cell align="left" valign="middle"><c>complete</c></cell>
726
<cell align="left" valign="middle"><c>GUI</c></cell>
727
<cell align="left" valign="middle"><em>100</em></cell>
729
<tcaption>Results of complete, exclusive and selective decode</tcaption>
731
<p>Another interesting question is what the relation is between
732
a complete decode, an exclusive decode followed by
733
<c>decode_part</c> of the excluded parts and a selective decode
734
followed by a complete decode. Some situations may be compared to
735
this simulation, e.g. inspect a sub-value and later on look at
736
the entire value. The following table shows figures from this
737
test. The number of loops and time unit is the same as in the
742
<cell align="left" valign="top"><em>Actions</em></cell>
743
<cell align="left" valign="top"><em>Function</em> </cell>
744
<cell align="left" valign="top"><em>Time</em>(microseconds)</cell>
745
<cell align="left" valign="top"><em>ASN.1 spec</em></cell>
746
<cell align="left" valign="top"><em>% of time vs. complete decode</em></cell>
749
<cell align="left" valign="middle"><c>complete</c></cell>
750
<cell align="left" valign="middle"><c>decode/2</c></cell>
751
<cell align="left" valign="middle"><c>4507457</c></cell>
752
<cell align="left" valign="middle"><c>MEDIA-GATEWAY-CONTROL</c></cell>
753
<cell align="left" valign="middle"><em>100</em></cell>
756
<cell align="left" valign="middle"><c>selective and complete</c></cell>
757
<cell align="left" valign="middle"><c>decode_­MegacoMessage_­selective/1</c></cell>
758
<cell align="left" valign="middle"><c>4881502</c></cell>
759
<cell align="left" valign="middle"><c>MEDIA-GATEWAY-CONTROL</c></cell>
760
<cell align="left" valign="middle"><em>108.3</em></cell>
763
<cell align="left" valign="middle"><c>exclusive and decode_part</c></cell>
764
<cell align="left" valign="middle"><c>decode_­MegacoMessage_­exclusive/1</c></cell>
765
<cell align="left" valign="middle"><c>5481034</c></cell>
766
<cell align="left" valign="middle"><c>MEDIA-GATEWAY-CONTROL</c></cell>
767
<cell align="left" valign="middle"><em>112.3</em></cell>
770
<cell align="left" valign="middle"><c>complete</c></cell>
771
<cell align="left" valign="middle"><c>decode/2</c></cell>
772
<cell align="left" valign="middle"><c>5889197</c></cell>
773
<cell align="left" valign="middle"><c>GUI</c></cell>
774
<cell align="left" valign="middle"><em>100</em></cell>
777
<cell align="left" valign="middle"><c>selective and complete</c></cell>
778
<cell align="left" valign="middle"><c>selected_­decode_­Window1/1</c></cell>
779
<cell align="left" valign="middle"><c>6337636</c></cell>
780
<cell align="left" valign="middle"><c>GUI</c></cell>
781
<cell align="left" valign="middle"><em>107.6</em></cell>
784
<cell align="left" valign="middle"><c>selective and complete</c></cell>
785
<cell align="left" valign="middle"><c>selected_­decode_­Window2/1</c></cell>
786
<cell align="left" valign="middle"><c>6795319</c></cell>
787
<cell align="left" valign="middle"><c>GUI</c></cell>
788
<cell align="left" valign="middle"><em>115.4</em></cell>
791
<cell align="left" valign="middle"><c>exclusive and decode_part</c></cell>
792
<cell align="left" valign="middle"><c>decode_­Window_­status_­exclusive/1</c></cell>
793
<cell align="left" valign="middle"><c>6249200</c></cell>
794
<cell align="left" valign="middle"><c>GUI</c></cell>
795
<cell align="left" valign="middle"><em>106.1</em></cell>
797
<tcaption>Results of complete, exclusive + decode_part and selective + complete decodes</tcaption>
799
<p>Other ASN.1 types and values can differ much from these
800
figures. Therefore it is important that you, in every case where
801
you intend to use either of these decodes, perform some tests
802
that shows if you will benefit your purpose.
807
<title>Comments</title>
808
<p>Generally speaking the gain of selective and exclusive decode
809
in advance of complete decode is greater the bigger value and the
810
less deep in the structure you have to decode. One should also
811
prefer selective decode instead of exclusive decode if you are
812
interested in just one single sub-value.</p>
813
<p>Another observation is that the exclusive decode followed by
814
decode_part decodes is very attractive if the parts will be sent
815
to different servers for decoding or if one in some cases not is
816
interested in all parts.</p>
817
<p>The fastest selective decode are when the decoded type is a
818
primitive type and not so deep in the structure of the top
819
type. The <c>selected_decode_Window2</c> decodes a big constructed
820
value, which explains why this operation is relatively slow.</p>
821
<p>It may vary from case to case which combination of
822
selective/complete decode or exclusive/part decode is the fastest.</p>
added
removed
lib/asn1/doc/src/asn1_spec.xml
