Add USE_FLOAT_EXCEPTIONS to enable floating point exceptions

[illwieckz]

• Add USE_FLOAT_EXCEPTIONS to enable floating point exceptions (disabled by default)
• Add USE_FAST_MATH to enable or disable fast math (enabled by default)

When USE_DEBUG_FPE is used, nothing is done unless some of those cvars are enabled:

• common.floatExceptions.invalid
• common.floatExceptions.divByZero
• common.floatExceptions.overflow

The USE_FLOAT_EXCEPTIONS option is required to specialize the build to make it possible to enable them.

[illwieckz]

I have not tested the Apple and MSVC code.

[illwieckz]

I renamed the cmake option to USE_FLOAT_EXCEPTIONS.

[slipher]

Wrong comment

[slipher]

Our code style is to have these on the left side and never indent them based on indentation of non-preprocessor code.

[illwieckz]

It's bad practice within a block, really.

[slipher]

What? This style is used very consistently in our code and is common in other code bases too. Preprocessor and non-preprocessor lines do not syntactically nest with each other, so it makes a sort of sense that neither one affects the other's indentation.

[slipher]

Not very accurate, cos(1.001) also does this for example

[slipher]

The use description of this is not quite accurate. It doesn't turn on exceptions; it alters compiler options in a way that makes the exceptions more likely to be useful. Maybe you could call it USE_FLOAT_DEBUG_MODE or something

[slipher]

Actually I think the name is fine but it would be good to mention the cvars. Enable floating point exceptions with common.floatException.* cvars

[illwieckz]

Hmm, my mac doesn't support more than Catalina, so no more than macOS 10.15.7 with Clang 12.0.0, and I get these errors:

src/engine/framework/System.cpp:319:19: error: use of
      undeclared identifier '__fpcr_trap_invalid'
                                exceptions |= __fpcr_trap_invalid;
                                              ^
src/engine/framework/System.cpp:331:19: error: use of
      undeclared identifier '__fpcr_trap_divbyzero'
                                exceptions |= __fpcr_trap_divbyzero;
                                              ^
src/engine/framework/System.cpp:343:19: error: use of
      undeclared identifier '__fpcr_trap_overflow'
                                exceptions |= __fpcr_trap_overflow;
                                              ^
src/engine/framework/System.cpp:356:8: error: no member named
      '__fpcr' in 'fenv_t'
                        env.__fpcr = env.__fpcr | exceptions;
                        ~~~ ^
src/engine/framework/System.cpp:356:21: error: no member named
      '__fpcr' in 'fenv_t'
                        env.__fpcr = env.__fpcr | exceptions;

So I cannot test macOS right now.

[illwieckz]

I face a weird cmake bug, if I do that:

	if (USE_FLOAT_EXCEPTIONS)
		message(STATUS "test true")
		# Floating point exceptions requires trapping math
		# to avoid false positives on architectures with SSE.
		set_c_cxx_flag("-ffp-model=strict")
	endif()

The “test true” message is printed, but the -ffp-model=strict flag isn't set.

But if I do:

	set_c_cxx_flag("-ffp-model=strict")
	if (USE_FLOAT_EXCEPTIONS)
		message(STATUS "test true")
		# Floating point exceptions requires trapping math
		# to avoid false positives on architectures with SSE.
	endif()

The flag is set.

So to sum it up:

• I know the test is true,
• I know the block is executed,
• I know the function works,

but the whole combination doesn't work…

[illwieckz]

If I do instead:

	if (USE_FLOAT_EXCEPTIONS)
		message(STATUS "test true")
		try_c_cxx_flag(FFP_MODEL_STRICT "-ffp-model=strict")
		# Floating point exceptions requires trapping math
		# to avoid false positives on architectures with SSE.
	endif()

I get this printed:

-- test true
-- Performing Test FLAG_FFP_MODEL_STRICT
-- Performing Test FLAG_FFP_MODEL_STRICT - Success

But the flag is not added to the compiler command line.

On the contrary if I do that:

	try_c_cxx_flag(FFP_MODEL_STRICT "-ffp-model=strict")
	if (USE_FLOAT_EXCEPTIONS)
		message(STATUS "test true")
		# Floating point exceptions requires trapping math
		# to avoid false positives on architectures with SSE.
	endif()

I get this printed:

-- Performing Test FLAG_FFP_MODEL_STRICT
-- Performing Test FLAG_FFP_MODEL_STRICT - Success
-- test true

And the flag is added to the compiler command line.