Compare: https://github.com/ppy/osu/pull/26616
This came up elsewhere, namely in
https://github.com/ppy/osu/pull/28277#issuecomment-2133505958.
As it turns out, at least one beatmap among those whose scores had
unexpected changes in total score, namely
https://osu.ppy.sh/beatmapsets/971028#fruits/2062131, was using slider
velocity multipliers that were not a multiple of 0.01 (the specific
value used was 0.225x). This meant that due to the rounding applied to
`SliderVelocityMultiplierBindable` via `Precision`, the raw value was
being incorrectly rounded, resulting in incorrect conversion.
The "direct" change that revealed this is most likely
https://github.com/ppy/osu-framework/pull/6249, by the virtue of
shuffling the `BindableNumber` rounding code around and accidentally
changing midpoint rounding semantics in the process. But it was not
at fault here, as rounding was just as wrong before that change
as after in this specific context.
Stable does this:
46cd3a10af/osu!/GameplayElements/HitObjectManagerFruits.cs#L98-L102
I'd rather not say what I think about it doing that, since it's likely
to be unpublishable, but to approximate that, just make it so that
only the "default fail condition" is beholden to the weird ebbs
and flows of what the ruleset wants. This appears to fix the problem
case and I'm hoping it doesn't break something else but I'm like 50/50
on it happening anyway at this point. Just gotta add tests add nauseam.
Fixes issue that occurs on *about* 246 beatmaps and was first described
by me on discord:
https://discord.com/channels/188630481301012481/188630652340404224/1154367700378865715
and then rediscovered again during work on
https://github.com/ppy/osu/pull/26405:
https://gist.github.com/bdach/414d5289f65b0399fa8f9732245a4f7c#venenog-on-ultmate-end-by-blacky-overdose-631
It so happens that in stable, due to .NET Framework internals, float
math would be performed using x87 registers and opcodes.
.NET (Core) however uses SSE instructions on 32- and 64-bit words.
x87 registers are _80 bits_ wide. Which is notably wider than _both_
float and double. Therefore, on a significant number of beatmaps,
the rounding would not produce correct values due to insufficient
precision.
See following gist for corroboration of the above:
https://gist.github.com/bdach/dcde58d5a3607b0408faa3aa2b67bf10
Thus, to crudely - but, seemingly accurately, after checking across
all ranked maps - emulate this, use `decimal`, which is slow, but has
bigger precision than `double`. The single known exception beatmap
in whose case this results in an incorrect result is
https://osu.ppy.sh/beatmapsets/1156087#osu/2625853
which is considered an "acceptable casualty" of sorts.
Doing this requires some fooling of the compiler / runtime (see second
inline comment in new method). To corroborate that this is required,
you can try the following code snippet:
Console.WriteLine(string.Join(' ', BitConverter.GetBytes(1.3f).Select(x => x.ToString("X2"))));
Console.WriteLine(string.Join(' ', BitConverter.GetBytes(1.3).Select(x => x.ToString("X2"))));
Console.WriteLine();
decimal d1 = (decimal)1.3f;
decimal d2 = (decimal)1.3;
decimal d3 = (decimal)(double)1.3f;
Console.WriteLine(string.Join(' ', decimal.GetBits(d1).SelectMany(BitConverter.GetBytes).Select(x => x.ToString("X2"))));
Console.WriteLine(string.Join(' ', decimal.GetBits(d2).SelectMany(BitConverter.GetBytes).Select(x => x.ToString("X2"))));
Console.WriteLine(string.Join(' ', decimal.GetBits(d3).SelectMany(BitConverter.GetBytes).Select(x => x.ToString("X2"))));
which will print
66 66 A6 3F
CD CC CC CC CC CC F4 3F
0D 00 00 00 00 00 00 00 00 00 00 00 00 00 01 00
0D 00 00 00 00 00 00 00 00 00 00 00 00 00 01 00
8C 5D 89 FB 3B 76 00 00 00 00 00 00 00 00 0E 00
Note that despite `d1` being converted from a less-precise floating-
-point value than `d2`, it still is represented 100% accurately as
a decimal number.
After applying this change, recomputation of legacy scoring attributes
for *all* rulesets will be required.
Closes https://github.com/ppy/osu/issues/25827.
The logic cannot be easily abstracted out (because
`CompareReverseChildID()` is protected and non-static on
`CompositeDrawable`), so a local copy was applied instead.
No testing as any testing would have been purely visual anyways.
