### absolute-mess's blog

By absolute-mess, 3 years ago,

Hello Coders!

I was doing this question High School: Become Human. I had to calculate x^y and y^x and take log on both sides...x(logy) and y(logx). When I submitted my solution, it got WA on TC3...where the TC was n=6 and m=6. The answer should be '=,' but the compiler showed '<'...Code in C++17 WA on 3. So why does 6(log6) != 6(log6), according to C++17, when I submitted the code for checking the value of 6log6 in this TC. It surprised me coz now the answer was showing '='... Code in C++17 for checking. But it got failed due to the value of n1 and m1 displayed. When I tried submitting the first code using C++20, it was accepted. AC on C++20.

I tried using Long double also, but it was of no use. https://codeforces.com/contest/987/submission/140238196

Can you somehow tell me why log, C++17, and C++20 behave in this strange manner and give weird output? I don't know why people are downvoting this, but if someone has the answer, do answer this.

Thanks!

• -8

| Write comment?
 » 3 years ago, # |   -9 Bahut bura hua bro !!!
•  » » 3 years ago, # ^ |   -9 Kya hi kar sakte hai...koi reason batado bas
 » 3 years ago, # |   0 Log always behave strange, because it's double arithmetic
•  » » 3 years ago, # ^ |   0 But why does it gives different answers to different compilers?
 » 3 years ago, # |   +5 Different compilers will work with floating point numbers differently. This is the reason why one should avoid using them if possible. That's all I know.
•  » » 3 years ago, # ^ |   0 Okay thanks
 » 3 years ago, # |   +9 I have previously written a blog about exactly this weirdness: Explanation of weird/strange floating point behaviour in C++The difference in floating point behaviour comes from the difference of compiling in 32 bit vs 64 bit. WA in C++17 (32 bit) 140239565AC in C++17 (64 bit) 140305850AC in C++17 (32 bit) if you use a pragma to turn off most of the weird floating point behaviour 140305892
•  » » 3 years ago, # ^ |   0 I read your blog and got my solution. Thanks a lot!One doubt: Will turning off weird floating-point behavior using pragma, will affect in some other way?
•  » » » 3 years ago, # ^ |   0 I'm really not sure what you are asking.I didn't show that pragma to tell you to use it. What you should do to avoid weird floating point issues in the future is to only use 64 bit C++. 64 bit C++ is superior in pretty much every way. To be honest, the only reason cf still supports 32 bit C++ is because of backwards compability.
•  » » » » 3 years ago, # ^ |   0 Okay, thanks!