Comparison floating points causes warning

[Finkman]

Treating warnings as errors causes Werror=float-equal on gcc 9.3 on NDEBUG

What is the issue you have?

I use JSON as an in-source library and compile the project with Werror and gcc 9.3.
json.hpp:14830:84 is then pointed out to be "unsafe".
The intention of that line is clear to me, but it should be considered to find a warning-free solution.

Please describe the steps to reproduce the issue.

Can you provide a small but working code example?

What is the expected behavior?

And what is the actual behavior instead?

Which compiler and operating system are you using?

• Compiler: gcc 9.3.0
• Operating system: Ubuntu 20.04

Which version of the library did you use?

• latest release version 3.9.1
• other release - please state the version: ___
• the develop branch commit: eb488bb

If you experience a compilation error: can you compile and run the unit tests?

• yes
• no - please copy/paste the error message below

[build] /home/fins/development/tqswip/tqs-wip-printer/libs/json/single_include/nlohmann/json.hpp:14830:84: error: comparing floating point with == or != is unsafe [-Werror=float-equal]
[build] 14830 |                 static_cast<double>(static_cast<float>(n)) == static_cast<double>(n))
[build]       |       

[t-b]

Well I think in this case the code really wants to check for hard equality without tolerance even if that is not very common for floating point values. I can only think of a workaround where the exponent/sign bit/mantissa is compared separately but that would be slower. Maybe silencing this warning here is the right thing to do?