Re: [DotGNU]my hacking notes

[Llewellyn Pritchard]

Thanks, that sounds great, I am for starters lost! but would love to know
more.

----- Original Message ----- 
From: "Gomi Kapoor" <address@hidden>
To: "pnet" <address@hidden>
Sent: Thursday, April 01, 2004 7:59 PM
Subject: [DotGNU]my hacking notes


> Hi all,
> While I am trying to understand the code of Portable
> .NET, I am attempting to write down a few things. I
> feel these notes would be helpful to other beginners
> like me. (the first one of them, please find attached
> with this mail.  It contains a small description of
> how the switch-case loop is split across different
> files).
>
> If you feel it is good, is there a place where I can
> host such small write
> ups? (or make it part of pnet/doc)
>
> Regards,
> Gomi Kapoor
>
> ________________________________________________________________________
> Yahoo! India Insurance Special: Be informed on the best policies,
services, tools and more.
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----------------------------------------------------------------------------
----


> Splitting a huge switch-case loop across mutiple files:
> ========= = ==== =========== ==== ====== ======= =====
> The Portable .NET's CIL (Common Intermediate Language) Verifier,
> CVM interpreter and the Unroller are implemented in the
> pnet/engine directory.
>
> The verifier is implemented in verify_* files, the CVM interpreter
> in cvm_* files and the unroller in unroll_* files.
>
> Interestingly all of them, involve implementing a huge switch-case
> loop and hence follow a similar coding style, which we discuss here.
>
> Instead of writing the whole huge switch-case loop in just a single
> file, it is split across many files as follows.
>
> Let's say we have a  file(loop.c), which has the actual switch-loop
> implemented and other files like loop_part1.c, loop_part2.c, where
> the relavent cases are implemented in those files. The whole loop is
> built by including those part files in the main file as follows:
>
> In file loop_part1.c, we have
> case LOOP_PART1_INST1:
> //...
> break;
> case LOOP_PART1_INST2:
> //...
> break;
> case LOOP_PART1_INST3:
> //...
> break;
>
> In the loop_part2.c, we have
> case LOOP_PART2_INST1:
> //...
> break;
> case LOOP_PART2_INST2:
> //...
> break;
> case LOOP_PART2_INST3:
> //...
> break;
>
> and finally in the file loop.c, we have
> void loop()
> {
> switch(...)
> {
> case LOOP_INST1:
> //...
> break;
> case LOOP_INST2:
> //...
> break;
> #include "loop_part1.c"
> #include "loop_part2.c"
> }
> }
>
> But one potential problem with the above implementation is, it is not
> possible to declare any local variables in the ``part'' files. All of
> them have to be in the main file and it becomes a bit difficult to
> manage in such a situation. Similar is the case if we need to have
> helper functions in the part files.
>
> These issues are addressed by using macros as shown below.
>
> In the part files, write the code can be written as follows:
> loop_part1.c:
> #if LOOP_GLOBALS
> //here goes the global variables and the helper functions
> #endif
>
> #if LOOP_LOCALS
> // Here goes the local varibales of the loop function
> // needed by the case
> #endif
>
> #if LOOP_MAIN
> //Here goes the actual code for the cases
> #endif
>
> And in the main file, loop.c we can have:
>
> #define LOOP_GLOBALS
> #include "loop_part1.c"
> #include "loop_part2.c"
> #undef LOOP_GLOBALS
>
> void loop(...)
> {
> #define LOOP_LOCALS
> #include "loop_part1.c"
> #include "loop_part2.c"
> #undef LOOP_LOCALS
>
> switch(...)
> {
> case LOOP_INST1:
> //.....
> break;
> .....
> #define LOOP_MAIN
> #include "loop_part1.c"
> #include "loop_part2.c"
> #undef LOOP_MAIN
> }
> }
> In the case of verifier:
>  Main file : verify.c (and the function is _ILVerify)
>  Part files : verify_ann.c
> verify_arith.c
> verify_branch.c
> verify_call.c
> verify_const.c
> verify_conv.c
> verify_except.c
> verify_obj.c
> verify_ptr.c
> verify_stack.c
> verify_var.c
>  Global Macro: IL_VERIFY_GLOBALS
>  Local Macro : IL_VERIFY_LOCALS
>  Cases Macro : IL_VERIFY_CODE
>
>
> In the case of CVM interpreter:
>  Main file : cvm.c (and the function is _ILCVMInterpreter)
>  Part files : cvm_var.c
>   cvm_ptr.c
> cvm_stack.c
> cvm_arith.c
> cvm_conv.c
> cvm_const.c
> cvm_branch.c
> cvm_call.c
> cvm_except.c
> cvm_compare.c
> cvm_inline.c
>  Global Macro: IL_CVM_GLOBALS
>  Local Macro : IL_CVM_LOCALS
>  Cases Macro : IL_CVM_MAIN, IL_CVM_WIDE, IL_CVM_PREFIX
>
> In the case of unroller:
>  Main file : unroll.c (and the function is _ILCVMUnrollMethod)
>  Part files : unroll_arith.c
>   unroll_branch.c
>   unroll_const.c
>   unroll_conv.c
>   unroll_ptr.c
>   unroll_var.c
>  Global Macro: IL_UNROLL_GLOBAL
>  Local Macro : -
>  Cases Macro : IL_UNROLL_CASES
>
>                               -*-*-*
>