doc/driver/limitations

This file contains a collection of non-configurable limits:

Program properties
==================
* maximum program length: 1 MB (1048575 Bytes)
  This is defined by FUNSTART_MASK in exec.h, which is the maximum offset
  (address) of a functions code within the program block (relativ to the
  beginning). Changing it involves changing funflag_t and probably other
  stuff.

* maximum number of programs: 2^32-1
  The unique program ID number is a int32. It is incremented for each compiled
  program. If it reaches zero (after wrapping to negative values) the
  compiler or swapper calls renumber_programs(), which recycles numbers from
  old programs.
  (exec.h, prolang.y, swap.c, ...)

* maximum number of functions in a program: 65534
  The lookup table for function indexes holding the offsets of the function in
  the functions tables is unsigned short.
  The types of function arguments are stored in program_s.argument_types,
  which is index by the unsigned short programs_s.type_start. 65535 has a
  special meaning. Some code relies that this is unsigned short.
  (exec.h, ...)
  program_s.num_function_names and num_functions are unsigned short as well.

* maximum length of switch: 256k (262143 Bytes)
  Limited by BREAK_ADDRESS_MASK and CONTINUE_ADDRESS_MASK?

* maximum offset for branches: 32765 (0x7ffd)
  (prolang.y)

* number of virtual variables: 256
* number of global variables: 65536 (F_IDENTIFIER16)
* number of local variables: 256 (F_PUSH_LOCAL_VARIABLE_LVALUE)
* number of context variables: 256 (Should be consistent with local
  variables, MAX_LOCAL applies to both. 16 bit opcodes are not used yet.)

* max number of struct members: 255
  (exec.h, ...)

* max number of structs per program: usually 32767 (short)


Hash tables
===========
* maximum size of the hash table for identifiers (ITABLE): 32768
  The hashes of identifiers are signed short which are in most cases 16 bit
  wide integers (lex.h, lex.c, ...)

* maximum size of the hash table for objects (OTABLE): 65536
* maximum size of the hash table for shared strings (HTABLE): 65536
  The hashes are of type unsigned short which are in most cases 16 bit
  wide integers.


Objects
=======
* maximum clone ID number: 2^32-1
  Not a real limitation, after that the driver starts checking if
  blueprint name + #cloneid are unique.


Memory management
=================
* max. size of single large block in slaballo.c and smalloc.c:
  0x07ffffff (134217727, defined by M_MASK)


Language
========
* maximum number of simul-efuns: 2048
  Only values 0xf800-0xffff in .x.closure_type of
  a T_CLOSURE svalue are reserved for simul-efuns.
  F_SIMUL_EFUN however takes a short int, so there 65536
  simul-efuns would be possible.

* maximum number of python efuns: 2048
  Only values 0xe800-0xefff in .x.closure_type of
  a T_CLOSURE svalue are reserved for python efuns.
  F_PYTHON_EFUN however takes a short int, so there 65536
  python efuns would be possible.