FMod precision

[flossy83]

According to this it's expected behaviour, and I tested it in C++ and got the same result as below:

string = 
\ "FMod(0.0, 0.1): " + String(FMod(0.0, 0.1)) + " (0.0 / 0.1 = " + String(0.0/0.1) + ")\n" +
\ "FMod(0.1, 0.1): " + String(FMod(0.1, 0.1)) + " (0.1 / 0.1 = " + String(0.1/0.1) + ")\n" +
\ "FMod(0.2, 0.1): " + String(FMod(0.2, 0.1)) + " (0.2 / 0.1 = " + String(0.2/0.1) + ")\n" +
\ "FMod(0.3, 0.1): " + String(FMod(0.3, 0.1)) + " (0.3 / 0.1 = " + String(0.3/0.1) + ")\n" +
\ "FMod(0.4, 0.1): " + String(FMod(0.4, 0.1)) + " (0.4 / 0.1 = " + String(0.4/0.1) + ")\n" +
\ "FMod(0.5, 0.1): " + String(FMod(0.5, 0.1)) + " (0.5 / 0.1 = " + String(0.5/0.1) + ")\n" +
\ "FMod(0.6, 0.1): " + String(FMod(0.6, 0.1)) + " (0.6 / 0.1 = " + String(0.6/0.1) + ")\n" +
\ "FMod(0.7, 0.1): " + String(FMod(0.7, 0.1)) + " (0.7 / 0.1 = " + String(0.7/0.1) + ")\n" +
\ "FMod(0.8, 0.1): " + String(FMod(0.8, 0.1)) + " (0.8 / 0.1 = " + String(0.8/0.1) + ")\n" +
\ "FMod(0.9, 0.1): " + String(FMod(0.9, 0.1)) + " (0.9 / 0.1 = " + String(0.9/0.1) + ")\n" +
\ "FMod(1.0, 0.1): " + String(FMod(1.0, 0.1)) + " (1.0 / 0.1 = " + String(1.0/0.1) + ")"

BlankClip.Text(string, lsp=0)

What's bugging me though is the values on the right side seem to imply the FMod result should have been 0, but obviously the precision internally is different than what is being shown.

And perhaps the bigger issue is why is the remainder 0.1 - shouldn't it be something really tiny like 1.49012e-08 or something?

I acknowledge that Avisynth is not doing anything technically wrong here - it's just returning whatever C++ says the FMod value is. Which kind of makes it useless - how are we supposed to do a check to ignore really tiny remainders if we're getting such a huge remainder on ones like FMod(0.5,0.1)?

[dartheditous]

0.1 in IEEE floats is actually slightly larger than 0.1, but 0.5 is exactly 0.5.

So only four 0.1s can fit in 0.5. The remainder is therefore slightly less than 0.1 (but the output gets rounded).

Most of the those 0.00000s are probably some really small non-zero number that isn't being fully displayed.