SecuritySNACCRuntime/tbl-example/README

   1 (RCS control information is at the end of this file.)
   2
   3
   4 Table encoder/decoder example README - MS 93
   5 ------------------------------------
   6
   7 This directory contains an example that shows:
   8
   9    1. the process of creating and using tables.
  10    2. examples of decoding, printing, and encoding.
  11
  12
  13 To dive right in just type "make" in this directory.  That will
  14 create the "example" executable (you should have previously installed
  15 the snacc and mkchdr progs and the table library).
  16
  17 Then type:
  18
  19  make check
  20
  21 and see what happens. Look in example.c and makefile to see how things
  22 work.
  23
  24
  25
  26 Questions and Answers
  27 ---------------------
  28
  29 Q. What is a table? (also refered to a type table or type tree)
  30
  31 A. A table is simply a data structure that holds a description of
  32    the types from an ASN.1 module.  This table can then be used
  33    by a number of "generic" routines to do ASN.1 related (BER
  34    encoding/decoding) or other useful things such as printing
  35    values, freeing values and whatever else you can dream up.
  36
  37
  38 Q. How do I create a table from my ASN.1 source files?
  39
  40 A. Run snacc with the -T option, e.g.:
  41
  42      snacc -T mytbls.tt myMod1.asn1 myMod2.asn1
  43
  44    the above command will create the "mytbls.tt" file that
  45    holds the descriptions of the ASN.1 types in the "myMod1.asn1"
  46    and "myMod2.asn1" files. (look in the makefile in this directory)
  47
  48
  49 Q. Why is there only a C interface to tables?
  50
  51 A. Time. Tables drivers create/read/free these types
  52    without having seen a typedef for them.  The C implementation
  53    uses some assumptions about how structures etc. are allocated
  54    and accessed.  With C++ this is much more difficult.  It can
  55    be done but required more time than I had.
  56
  57
  58 Q. Ok, tables sound great, what's the catch?
  59
  60 A. Well,
  61
  62    1. table driven encoding and decoding is something like
  63       4 times slower than the C or C++ version.
  64       (but tables are *way* smaller than the .o's for the compiled approach)
  65    2. the ANY DEFINED BY stuff is not supported at all.
  66    3. subtype information is not included in the tables (time crunch again)
  67       (PER encoders/decoders will need the subtype info)
  68    4. Values from the ASN.1 source are not included in the table.
  69
  70    If you have the time and skills, you can fix 2, 3 and 4.  1 is harder.
  71
  72
  73
  74 Q.  Tell me more.
  75
  76 A.  Look at the manual. (in .../doc/)
  77
  78 #-------------------------------------------------------------------------------
  79 # $Header: /cvs/Darwin/Security/SecuritySNACCRuntime/tbl-example/README,v 1.1.1.1 2001/05/18 23:14:10 mb Exp $
  80 # $Log: README,v $
  81 # Revision 1.1.1.1  2001/05/18 23:14:10  mb
  82 # Move from private repository to open source repository
  83 #
  84 # Revision 1.1.1.1  1999/03/16 18:06:54  aram
  85 # Originals from SMIME Free Library.
  86 #
  87 # Revision 1.1  1997/02/15 19:33:24  rj
  88 # first check-in
  89 #