Bugs and questions
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- Subject: Bugs and questions
- From: "mvezzosi@libero."<mvezzosi@...>
- Date: 2000年5月11日 09:59:22 +0200
Hi all
Introduction:
I'm using Lua as a stand-alone language for the MSDOS and the Nokia 9110
Communicator (a GSM phone with PDA functions; its operating system runs
on top of Embedded DOS-ROM which is mostly compatible with MS-DOS). For
this reason, I compile Lua for a 16 bit environment and my compiler
consider the Int C type composed by 16 bits.
Bugs and notes:
1) In lmem.h the macros
#define luaM_newvector(n,t) ((t *)luaM_malloc((n)*sizeof(t)))
#define luaM_reallocvector(v,n,t) ((v)=(t *)luaM_realloc(v,(n)
*sizeof(t)))
can pass a wrong size value to luaM_realloc() if Int is composed by 16
bits and "n" is big enough.
For example, this program hangs at the 2136th loop, when Lua grows the
memory allocated for the table "t":
t = { }
n = 0
while 1 do
t[n] = n
n = n + 1
print(n)
end
IMO the macros should contains a cast to unsigned long:
#define luaM_newvector(n,t) ((t *)luaM_malloc((unsigned
long)(n)*sizeof(t)))
#define luaM_reallocvector(v,n,t) ((v)=(t *)luaM_realloc(v,(unsigned
long)(n)*sizeof(t)))
I have't made a complete search, but I think that the following
functions can have the same 16 bit related problem. Please note that I
just had a look at this source codes without study them in depth
(particularly for the 4.0), so could be wrong:
- lbuffer.c->openspace(): if (L->Mbuffnext+(size) > L->Mbuffsize) ...
- lbuffer.c->Openspace():
- 3.2: size += EXTRABUFF;
For example:
a = strrep("A", 16380)
b = strrep("B", 16380)
c = a .. b
gives correctly "lua error: internal array bigger than `int' limit
" because in lmem.c->luaM_growaux() the lines
unsigned long newn = nelems+inc;
if (newn >= limit) lua_error(errormsg);
have the values of
unsigned long (4294934552) = (0)+(-32744);
if ((4294934552) >= (32765)) lua_error(errormsg);
("inc" has the value of Openspace()'s "size")
Is it the right behaviour or only fortune ?
- 4.0: L->Mbuffsize = (L->Mbuffnext+size+EXTRABUFF)*2;
2 e 4.0 (should be very rare):
Closure *c = (Closure*)luaM_malloc(sizeof(Closure)+nelems*sizeof
(TObject));
- lundump.c->LoadCode():
- 3.2: Byte* b=luaM_malloc(size+PAD);
- 4.0 (I don't know if this line can gives problems or not):
LoadBlock(L,tf->code,size*sizeof(*tf->code),Z);
2) Lua 4.0:
- lparser.c->listfields(): checklimit(ls, n,
MAXARG_A*LFIELDS_PER_FLUSH, "...") gives "'*' : integral constant
overflow; result truncated" on my 16 bit compiler, because MAXARG_A is
2^17-1 and LFIELDS_PER_FLUSH is 64 and their product is greater than
32767.
- lbuiltin.c->luaB_predefine() with the macro DEBUG defined:
luaB_opentests() gives "unresolved external" (there is also the
function's prototype at line 44). IIRC, this warning was already posted
but related to luac and without DEBUG.
- In manual.html at "8 - Lua Stand-alone" is missing the explanation
of the -s argument.
3) In interactive mode, after entering the line (for examples)
a, b = read("*n", "*n")
Lua displays 2 prompts ("> >").
Questions:
1) Sometimes I need to return the elements of a table as single
variables. For examples:
function read(...)
dosomething()
local retlist = call(%read, arg, "p")
dosomethingelse()
return tunpack(retlist) [see forward for tunpack()]
end
a, b = read("*n", "*n")
To do this, I wrote this function:
function tunpack(tbl)
if (tbl == nil) or (tbl.n == nil) or (tbl.n == 0) then return
end
local tbl1 = tbl[1]
tremove(tbl, 1)
return tbl1, tunpack(tbl)
end
Is there a better way to do this ? (I would like to avoid the
recursion's overhead and to destroy the table)
2) At the moment, I also use tunpack() to return a variable number of
values. For example:
function example(flags)
local ret = { }
if strfind(flags, "A") then tinsert(ret, dosomething()) end
if strfind(flags, "B") then tinsert(ret, dosomethingelse()) end
...
return tunpack(ret)
end
a, b
Is there a better way to do this instead of using a table ?
3) Is it possible to avoid the assignment of some arguments in the "="
operator ? For example something like:
nil, a, nil, b = dosomething()
, a, , b = dosomething()
I could write
a, a, a, b = dosomething()
but this involves always 4 assignments even if I need only the last one.
I still have a couple of questions about memory management to reduce and
recover the memory allocation but I don't want to bother you too much
with this email.
Sorry for this long email and for my wrong English.
TIA
Best regards
Mauro