Re: [patch] fix luai_num* null states

[Lourival Vieira Neto <lourival.neto@...>]

On Tue, Mar 4, 2014 at 3:34 PM, Roberto Ierusalimschy
<roberto@inf.puc-rio.br> wrote:
>> > I had another small issue on luaV_numtointeger(). I had an 'integer
>> > overflow' on the line 81 of lvm.c. I solved as follows:
>> >
>> > -  if (cast_num(MIN_INTEGER) <= n && n < (MAX_INTEGER + cast_num(1))) {
>> > +  if (cast_num(MIN_INTEGER) <= n && (n - cast_num(1)) < MAX_INTEGER) {
>>
>> This is tricky... In my machine, this change does not pass the standard
>> tests for vanilla Lua (64-bit floats and integers). (I am trying to figure
>> out why, but when I add some printfs to the code, it works again; weird...)
>
> With the new code, the machine does all computations for
> (n - cast_num(1)) < MAX_INTEGER in registers, with more precision than
> 64 bits. We do need the "overflow" here to get the right result.
> (Think when 'n' is 2.0^63, which does not fit into a 64-bit integer.)

Sorry,  it really sounds tricky.. I don't get it yet =(.. in that
case, we should have a float comparison, don't we? Thus, the '<'
expression would return 0, the 'if' test would fail and the function
would return 0, which should be the right result for n = 2.0^63. Is
that wrong? I must be missing something.

BTW, these tests are publicly available for Lua 5.3?

Regards,
-- 
Lourival Vieira Neto