Strange math behaviour... could someone explain this ?

[Lynch, Jonathan]

Further confirmation of what JB noticed:

This:
round(((36-34.2)*100)-.5)

also returns 179, when it should return 180.

So the problem is not in the trunc function itself, it is in the way Rev
performs a calculation like 36-34.2   -- How many accounting errors
might this have caused for people?

-----Original Message-----
From: use-revolution-bounces at lists.runrev.com
[mailto:use-revolution-bounces at lists.runrev.com] On Behalf Of Lynch,
Jonathan
Sent: Friday, October 07, 2005 9:32 AM
To: How to use Revolution
Subject: RE: Strange math behaviour... could someone explain this ?

Even just this simple line produces the same error:

answer trunc((36-34.2)*100)

This is odd...

Look at the results I get when testing this:

Trunc((36-34.1)*100) should = 190, but returns 189
Trunc((36-34.2)*100) should = 180, but returns 179
Trunc((36-34.3)*100) should = 170, and in fact does return 170
Trunc((36-34.4)*100) should = 160, and in fact does return 160

Trunc((1.8)*100) returns 180, like it should
Trunc((1.9)*100) returns 190, like it should

So...

Somehow, Rev is performing 36-34.2, and even though it displays that
number as 1.8, it must be processing it internally as
1.799999999999999999999999999 or something like that.

Very disturbing - This could affect a program of mine.

It is easily worked around, with a function like this:

function trueTrunc pNumber
  set the itemdelimiter to "."
  return item 1 of pNumber
end trueTrunc

But still, trunc should work properly. That makes me wonder if any other
math functions might have some underlying weirdness.



-----Original Message-----
From: use-revolution-bounces at lists.runrev.com
[mailto:use-revolution-bounces at lists.runrev.com] On Behalf Of Lynch,
Jonathan
Sent: Friday, October 07, 2005 9:13 AM
To: How to use Revolution
Subject: RE: Strange math behaviour... could someone explain this ?

I get the same thing...

That's gotta be a bug.


-----Original Message-----
From: use-revolution-bounces at lists.runrev.com
[mailto:use-revolution-bounces at lists.runrev.com] On Behalf Of jbv
Sent: Friday, October 07, 2005 7:17 AM
To: How to use Revolution
Subject: Strange math behaviour... could someone explain this ?

Hi list,

example 1 :

  put 1.8 into myA
  put trunc(myA * 100) into myA

  in that case, myA=180    which is OK
------------------

example 2 :

  put 34.2 into myA
  put 36 into myT

  if myA > 0 then
    if myA < myT then
      get myA
      put myT - myA into myA
      put it into myT
    else
      put 0 into myA
    end if
  end if

  put trunc(myA * 100) into myA

  in that case, myA=179    ?????????????????????


Best,
JB

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