math.asm test failure with armv7a-unknown-linux-gnueabihf about rgbds HOT 6 CLOSED

Oh god, here come the floating-point nightmares. Can you add a println FMOD(-5.0, 0.0) line, and re-run? (The location within the file doesn't matter. It will be printed as another diff, so no need to change anything else either.)

from rgbds.

As I stated I lack this hardware, but I asked the reporter if they can help test.

If not I can try to cross-compile it later...

from rgbds.

The issue here is that the result of those operations is, respectively, infinity and NaN. Those values don't convert to integers cleanly. Some CPUs do it one way, some do it another way. Converting infinity or NaN to an integer in C is definitely UB and not portable in the slightest.

from rgbds.

Since rgbasm just has fixed-point, I'd suggest converting Infinity to the maximum positive value, -Infinity to the maximum negative value, and NaN to 0 (same as how various other non-asm-time-computable expressions become 0).

from rgbds.

It might be possible to reproduce this on x86_64 using ubsan with clang ( 18.1.2).

FLAGS='-O0 -g -fno-omit-frame-pointer -fsanitize=undefined' && make Q= CXXFLAGS="$FLAGS" LDFLAGS="$FLAGS" CXX=clang++

math...
--- /dev/null	2024-03-23 23:47:52.120956538 -0700
+++ /tmp/tmp.0Tczm9DMP3	2024-03-30 19:17:50.224177174 -0700
@@ -0,0 +1,2 @@
+src/asm/fixpoint.cpp:28:18: runtime error: -inf is outside the range of representable values of type 'int'
+SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior src/asm/fixpoint.cpp:28:18 
math.err mismatch!

from rgbds.

Honestly, I'd suggest a simple if (!isfinite(value)) value = 0; fix for all floats before being converted back to fixed — there's simply no reasonable representation for infinity or NaN, so you might as well kill the problem in one go.

from rgbds.