Closed Whoome closed 1 year ago
The overflow check takes a lot run-time.
A small fix is to use int64. This is a option when you create the runtime new Lua(LuaIntegerType.Int64)
.
May be I should introduce an option, that always double is used.
I did a bit more playing around and I -think- lua 5.3 is using int64 as the default. I tweaked up my code:
function CountTo(xx)
local sum = 0
local lastSum = 0
for i=1,xx do
sum = sum+i
if(math.type(sum) ~= 'integer') then
printline(string.format("Sum is not an integer. i==%d, sum == %f", i, sum))
break
end
if(sum < lastSum) then
printline(string.format("Sum Wrapped. i==%d, sum == %f", i, sum))
break
end
lastSum = sum
end
return sum
end
And the print never triggered. Sum stayed an integer out to 500000500000 which is out of the Int32 range (even UInt32) so it must be using 64 bit ints. I think that would probably suggest that is the appropriate default for NeoLua as well.
Unfortunately even when I set the default int to LuaIntegerType.Int64 I still have the issue in NeoLua:
--Test that we have int64 working
>q = 500000500000
>print(math.type(q))
integer
>printline(q)
500000500000
>print(CountTo(1000000))
Sum Wrapped. i==65536, sum == -2147450880.000000
I'm not sure why, I haven't dug in yet - but something is truncating it. I -suspect- it is the for loop ignoring the integer type:
>for i=0, 1 do printline(tostring(i)) end
0
1
>for i=500000500000, 500000500001 do printline(tostring(i)) end
Exception: Argument types do not match
Though even if (as it seems) that stays an int32 - I don't see why it truncates something is causing the result of the add to truncate.
NeoLua Version: 1.3.14
Example to reproduce:
This prints 1784293664, which is not the correct answer. Lua 5.3 prints the correct answer: 500000500000.
Now, obviously what I have done is run the integer over. but 5.3 natively handles it by starting to use a double. If I change the function slighty:
Then NeoLua behaves ok. What I am worried about more than anything is the silent failure when wrapping the int - it makes it hard and very very subtle to find issues when moving to NeoLua from Lua 5.3.
Thanks!