Re: [Adobe-source-devel] Questions about sheet_t::implementation::get

[Sean P. <sea...@ma...>]

Hi cee1,

Welcome! Questions on ASL are always appreciated. I'm not sure which  
version of the code you're referring too, the line numbers don't match  
up with the current release. I'm going to use the latest code from my  
sanbox here:

http://stlab.adobe.com:8080/@lno=y@//sandbox/sparent/adobe_source_libraries/source/adam.cpp?ac=64&rev1=28

On Dec 13, 2009, at 5:17 AM, cee1 wrote:

> Hi all,
> I'm reading the code of adam.cpp, and get totally lost.

It is a bit twisty - I've been slowing working on a rewrite using  
Boost Graph Library - but no ETA on when that will appear.

> In the function sheet_t::implementation_t::get:
> (adam.cpp 1387) "if (initialize_mode_m) { ..."
> I've found initialize_mode_m is false when instantiates  
> sheet_t::implementation_t, and will be true when calls add_constant,  
> add_input or add_interface. So the following assert should always  
> fail:

(line 1435 in my copy) When a sheet is constructed, initializers are  
evaluated as  the cells are added. the get() function is called by the  
expression evaluator to look up variables. The expressions on a sheet  
initializer can only refer to cells that have been previously declared  
(added to the sheet) and the initializers don't attempt to follow  
relationships, they only pick up the cell value of previously  
initialized cells.

> (adam.cpp 1428) assert(cell.interface_input_m && ...),
> Because when this line is reached, the initialize_mode_m is false,  
> then we should not have called add_constant, add_input or  
> add_interface, so the cell is not an interface cell, assert failed.

(line 1476) - there is a return statement on line 1449 so this line is  
not going to be reached if initialize_mode_m is true.
>
> Also, I find some code that makes no sense to me, like:
> (adam.cpp 1267) sheet_t::implementation_t::initialize_one
> accumulate_contributing_m.reset();
> ...
> cell.init_contributing_m |= accumulate_contributing_m;

(1315) accumulate_contributing_m is a member variable that holds a bit  
field corresponding to cells. Executing calculate_m() on line 1323 is  
going to set the bits for the cells that are read as part of that  
expression in accumulate_contributing_m. Then on line 1325 that bit  
set is or'ed with the other bits contributing to the initializer on  
that cell.

>
> or
>
> (adam.cpp  1173) in function sheet_t::implementation_t::update
> if (cell.specifier_m == access_interface_output)  
> get_stack_m.push_back(std::make_pair(cell.name_m, false));

(1221) The get_stack_m is used to detect self-referential expressions  
in get() (which is called as part of calculating an expression for  
variable lookup). For example, if you have a rule like:

a <== max(a, b);

Then the lookup of "a" is self referential, and must refer to the  
initial value of "a", but "b" is not self referential and will refer  
to the final value of "b".

See line 1475 for where this is used.

> ...
> if (cell.specifier_m == access_interface_output)  
> get_stack_m.pop_back();
>
>
> Sorry for this mass mail, but I feel lost in adam.cpp. Could someone  
> show me the global picture of how these functions in  
> sheet_t::implementation work?

No problem - keep the questions coming.

Sean

>
>
> Regards,
> - cee1
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