here's why math is fun... to mess with.

messing with java and computercraft is fun. for example, try these things

>lua
welcum to lua
now u do magic with lua
lua>print(tostring(2^15))
yeah, that is normal.
lua>print(tostring(2^127))
that would be a big number. now for the fun part.
lua>print(tostring(2^128))
what does it return?
Infinity0

yeah, that's something fun to do. now for something confusing.

a = 1
for i = 1,127 do
a = a/2
print(a)
sleep(0.1)
end
print(a)

that's a fun one. now try this.

a = 1
while not a==0 do
a = a/2
print(a)
sleep(0.1)
end
print(a)

why does that return 1?
just how fun it is.
got any cool things to try? leave a reply with what it is.

The first one is "normal" behaviour. The number you tostring is just so big that is comes out as infinite and the 0 is added because of the way print and tostring works. It looks like tostring returns 2 things. A string and a number (i have no idea what the number does). Print concatenates every argument you give it with "" so the 0 (second argument) is sticked to the end of the string (first argument). :P/>

H4X0RZ, on 08 August 2015 - 03:37 AM said:

The first one is "normal" behaviour. The number you tostring is just so big that is comes out as infinite and the 0 is added because of the way print and tostring works. It looks like tostring returns 2 things. A string and a number (i have no idea what the number does). Print concatenates every argument you give it with "" so the 0 (second argument) is sticked to the end of the string (first argument). :P/>

nice explaination, and i also have a theory.
Java uses tones of number variable types, and if they are really big (don't say that's what she said) then it can break the code.
the biggest i know (oh, don't even think about it) is a long, which is 2^63.
it is like 128, but the max is always 2^(num-1) so the max is 2^127.
this is why when you show all 16 bit colors you do 2^1 - 2^15

yeah, that totally made sense.

It's returning 1 on your third test because you're failing to account for operator precedence. not evaluates before ==, so your statement is checking to see if false == 0, which of course it isn't. A better way to write that statement is:

while a ~= 0 do

Mathematically speaking the loop should be infinite because the series of rational numbers is theoretically infinite, but the loop will terminate (at around 1/2^1075 in my tests) because computers have finite precision.This is also why you should never compare floating point numbers for equality in this manner.

Here's a bit of code to demonstrate why it's bad practice:

a = 11111111113
b = -11111111111
c = 7.51111111111
print(a + (b + c))
print((a + b ) + c)
if (a + b ) + c == a + (b + c) then
  print("FP arithmetic is associative")
else
  print("FP arithmetic is not associative")
  print(math.abs(((a + b ) + c) - (a + (b + c))))
end

Also, while longs and doubles are the largest primitive number types, remember Java also has BigInteger and BigDecimal, which are arbitrary precision.

Edit: Don't capitalize the B's. I have no idea why the forum editor is doing that.

nitrogenfingers, on 19 August 2015 - 08:12 AM said:

Edit: Don't capitalize the B's. I have no idea why the forum editor is doing that.

Because you're using the code for emoticons. Disabling them via the full editor sorts it out.

nitrogenfingers, on 19 August 2015 - 08:12 AM said:

a = 11111111113
b = -11111111111
c = 7.51111111111
print(a + (b + c))
print((a + b ) + c)
if (a + b ) + c == a + (b + c) then
  print("FP arithmetic is associative")
else
  print("FP arithmetic is not associative")
  print(math.abs(((a + b ) + c) - (a + (b + c))))
end

That's pretty interesting (spoiler: it prints out "not associative"). I've been flummoxed before when my various math related things were evaluating things incorrectly, even when I was printing out the values beforehand, doing the math myself, and getting a correct answer. I've always defaulted to using a function like this to try and avoid the issue:

function roughlyEqualTo( a, b )
     return math.abs( a - b ) < .0001
end

…but I never thought it could be a difference between the order in which things were added! That's crazy.