undefined | Better HN

0 pointsgdxhyrd6y ago0 comments

All major C/C++ compilers implement IEEE754. If you are telling the compiler to disregard it, that is on you.

0 comments

It's not about IEEE754, it's about the precision that the FP co-processor offers. The results you get are correct per IEEE754, it's just that they may have even less error than required by IEEE754 in some cases. But, this is enough to make the results non-deterministic between different compilation options.

Also, changes applied to the FP co-processor by other processes on the machine could impact your process, regardless of your own compilation settings.

chrisseaton6y ago

Are you talking about x87?

That's ancient history. Compilers don't use that instruction set any more in normal operation.

GCC, Java, LLVM, etc, will normally emit SSE2 in order to be standards compliant. They will only relax this if you tell them to, then it's your problem.

tsimionescu6y ago

Yes, I was explicitly talking about the x87, and did mention that it has stopped being relevant for at least 10 years.

I believe there is still quite a bit of cautionary discussion of floating point numbers that was written in the age of the x87, so it's important to understand that people were not just misunderstanding IEEE754, even though their concerns are no longer applicable to modern hardware.

j / k navigate · click thread line to collapse

0 comments

tsimionescu6y ago

Also, changes applied to the FP co-processor by other processes on the machine could impact your process, regardless of your own compilation settings.

chrisseaton6y ago

Are you talking about x87?

That's ancient history. Compilers don't use that instruction set any more in normal operation.

GCC, Java, LLVM, etc, will normally emit SSE2 in order to be standards compliant. They will only relax this if you tell them to, then it's your problem.

tsimionescu6y ago

Yes, I was explicitly talking about the x87, and did mention that it has stopped being relevant for at least 10 years.

j / k navigate · click thread line to collapse