topic Re: Programming Trivia Pop Quiz: Be Different! in BreakPoint

Programming Trivia Pop Quiz: Be Different!

altenbach — Tue, 08 Aug 2017 16:25:34 GMT

Unlike the last question, this one should be common knowledge for everybody.

QUESTION: Find a value that will cause the boolean to be TRUE when the code is executed.

Re: Programming Trivia Pop Quiz: Be Different!

crossrulz — Tue, 08 Aug 2017 16:36:02 GMT

This one is too easy

There is not a number that will return TRUE here.

Re: Programming Trivia Pop Quiz: Be Different!

jwscs — Wed, 09 Aug 2017 10:41:09 GMT

answer:

might this be a trick question?
i know that you cannot guarantee x + (y+z) == (x+y)+z for floating points,
but to compare the same number/bit-representation against each other should never be different.

Re: Programming Trivia Pop Quiz: Be Different!

Ben — Wed, 09 Aug 2017 13:01:06 GMT

@jwscs wrote:

answer:

might this be a trick question?
i know that you cannot guarantee x + (y+z) == (x+y)+z for floating points,
but to compare the same number/bit-representation against each other should never be different.

If you look at the definition of floating point numbers, there is a case where it SHOULD be different.

That condition is what Christian is trying to teach us about with this trivia question.

Ben

Re: Programming Trivia Pop Quiz: Be Different!

jwscs — Wed, 09 Aug 2017 14:02:04 GMT

ok found it...

thought about NaN .. but searched for a constant, didn't enter my mind before to just write it in 😉

guess from mathematical standpoint it makes sense, since the value is undefined
links: https://en.wikipedia.org/wiki/IEEE_754#Formats
https://stackoverflow.com/questions/1565164/what-is-the-rationale-for-all-comparisons-returning-false-for-ieee754-nan-values

Re: Programming Trivia Pop Quiz: Be Different!

BowenM — Wed, 30 Aug 2017 21:24:41 GMT

My first guess was either +inf or -inf. Interestingly enough, this returns false. I guess you could prove that a double precision float is countably infinite...

Re: Programming Trivia Pop Quiz: Be Different!

jwscs — Thu, 31 Aug 2017 15:03:44 GMT

@BownM i must disagree with you, since you only have a finite number of bytes for the representation, it follows, that there can only be a finite number of different numbers.

Re: Programming Trivia Pop Quiz: Be Different!

altenbach — Thu, 31 Aug 2017 17:28:13 GMT

According to IEEE-754, there is exactly one unique bit pattern for +inf and -inf, respectively. However, there is a huge number of different NaNs. (details)

Re: Programming Trivia Pop Quiz: Be Different!

Yamaeda — Mon, 04 Sep 2017 08:49:31 GMT

@jwscs wrote:

@BownM i must disagree with you, since you only have a finite number of bytes for the representation, it follows, that there can only be a finite number of different numbers.

Approximately 18.4*10^18 unique combinations. 🙂

Re: Programming Trivia Pop Quiz: Be Different!

FengQingYang — Fri, 08 Sep 2017 01:57:36 GMT

- input value:NAN