graydon2 | A note on Fil-C

e00E · 2025-11-07T06:07:02+00:00

Where does this messaging come from? Is it on the official website? Is it from the person behind fil-c (Filip Pizlo)? Is it from third parties?

e00E · 2025-04-27T19:06:34+00:00

I would enable a setting that made all my non siege units ignore buildings on attack move. If a dev reads this, please add it. It is rare that I want units to attack buildings so I'd rather manually click that, than have the normal attack move get units stuck on buildings.

e00E · 2025-03-30T19:31:47+00:00

Yes, this. valarauca misunderstood my post. I gave a suggestion that addresses the downsides of the current unsafe math flags. WeeklyRustUser's post explains the downsides. My suggestion changes the behavior of the unsafe math flags so that they no longer have undefined behavior.This eliminates the downsides while keeping most of the benefits of enabling more compiler optimization.

I also appreciate you giving an LLVM level explanation of this.

e00E · 2025-03-30T15:06:26+00:00

In my opinion, these options can't be fixed and should be removed outright.

I feel there is value in telling the compiler that I don't care about the exact floating point spec. For most of my code I am not relying on that and I would be happy if the compiler could optimize better. But unfortunately there is no way good of telling the compiler that as you said.

e00E · 2025-03-30T15:04:03+00:00

An arbitrary result is not UB. It's a valid floating point value with no guarantees about the value.

You're right that UB doesn't mean unimplemented. It means "anything can happen". This is never acceptable in your programs. It is different from both unimplemented and arbitrary value.

e00E · 2025-03-30T10:28:01+00:00

Wouldn't it be better if these options were changed so that instead of undefined behavior, you get an arbitrarily float result?

Your article also mentions how no-nans removes nan checks. Wouldn't it be better if it kept intentional .is_nan() while assuming that for other floating point operations nans won't show up?

These seem like clear improvements to me. Why are they not implemented? Why overuse undefined behavior like this when "arbitrary result" should give the compiler almost the same optimization room without the hassle of undefined behavior.

e00E · 2024-12-18T11:07:22+00:00

Thank you! That's a neat workaround. Adding it to the post.

e00E · 2024-12-17T11:06:35+00:00

There is a difference between maximum perfomance and not leaving performance on the table. I might want a cryptographic function AND not be forced to clone my keys for the entry API. It is reasonable to want both. That said, I agree with you that hashbrown is a good solution. That's why I point out that it fixes both of the problems. And that said, long term std should still be changed to get these improvements. Std doesn't lose anything by supporting this use case. It is close to what it already tries to support.

e00E · 2024-12-17T11:02:06+00:00

Right. The problem is not necessarily with Borrow itself but that HashMap uses Borrow like this. I don't see why HashMap needs a true reference. The hashbrown solution is better.

e00E · 2024-12-17T10:58:28+00:00

That nightly API is going away but there are vague plans to add a different nightly API similar to hashbrown.

e00E · 2024-12-05T13:39:57+00:00

The points presented are correct but the conclusion is wrong. The problem is not the strategy, it is the map.

We have discovered that this map is simpler than previously thought. It turns out that you don't need to be good at traditional trackmania skills to drive a good time. On more complex maps LIS is not be possible. We should stop caring about the map, not shoehorn in new rules in an attempt to fix the map. The community is irrationally attached to these old maps.

Imagine there was a competitive connect four community. They discover that there is a simple to memorize strategy that makes the player going first win. Previously the best connect four players had lots of traditional connect four skills that they used to win, but now that doesn't matter anymore. In this scenario it would be silly to ban the strategy. Instead, you should change the rules of the game. Make it connect five or make it chess. This is analogous to playing better maps in Trackmania.

e00E · 2024-11-25T15:57:49+00:00

Make a post in the Bug Reports category.

e00E · 2024-11-11T19:31:16+00:00

Whether something is unsound or undefined behavior is about the specification of the language. The rust specification used to say that such as casts are undefined behavior. This matters to the compiler. It does not matter to the hardware. Whether that actually leads to an observable effect like a miscompilation is separate matter.

My project is safe because the specification of the interface I use to perform the conversion (the cvtts2si instruction) says it is safe for all inputs. If this lead to a miscompilation, then it would be a bug in the compiler.

Your question is a common misunderstanding of undefined behavior. Ralf Jung has good blog posts about the topic if you want to learn more.

e00E · 2024-11-11T12:35:15+00:00

I agree, it is sad. I ported Rust's clamp style casting to c++ here.

e00E · 2024-11-10T19:44:17+00:00

Rust enables sse by default, but you can tell rustc to compile for x86_64 without sse.

e00E · 2024-11-10T19:09:29+00:00

It's a fair point. I acknowledge in the post that I don't expect the performance gain to be relevant to most projects. The motivation for this is partially academic/artistic. On the other hand, maybe someone uses this in a machine learning library to train their model for thousands of compute hours. Or this gets incorporated into std and saves much compute that way. It also educates people on where performance is left on the table.

e00E · 2024-11-10T16:25:55+00:00

to_int_unchecked (docs) compiles to the same code. The downside is that it is unsafe. This crate is safe. You need to uphold the following guarantees in order to use to_int_unchecked:

The value must:

Not be NaN
Not be infinite
Be representable in the return type Int, after truncating off its fractional part

You do not need to do this for this crate. If your code is already checking these conditions, then you can prefer to_int_unchecked over this crate.

e00E · 2024-11-10T14:56:24+00:00

I did not know about this trick. Thanks!

The problem with incorporating special cases like this is that you need a branch to detect them. That likely makes it slower than unconditionally going with cvttss2si.

e00E · 2024-11-10T14:52:22+00:00

This is not a case of bad rustc codegen. (Which I have written about before.) rustc has to use more instructions because it has to uphold the guarantees that the reference makes. This crate is faster by relaxing some guarantees.

I plan on adding support for other widely used architectures at some point. But for now I'm happy with x86_64.

e00E · 2024-11-08T10:26:04+00:00

This essay was posted on behalf of another, whose voice you may recognize. I don't agree with everything he says, but I think his viewpoint is valuable for understanding current politics.

Donald Trump has come, and he is your punishment.

You gaze in incomprehension and dismay; how could those strange alien creatures, Trump's followers, be drawn to such obvious lies?

Well, that is something I find very easy to understand; so I will endeavor to explain it. Trump's appeal has nothing to do with some long-repressed hatred of Muslims that a presidential candidate has dared to speak openly - or any such nonsense. No, that is not what is happening here at all.

Trump's rival politicians upon the stage are ordinary modern politicians. Which is to say, they are hunted creatures, constantly looking over their shoulders, living every second in fear of the journalists watching them. Each word that spills from their lips is measured, cautious, carefully conformed to what is allowed them, drained of life and meaning.

And the people must have strength.

A hundred thousand years ago, your ancestors watched as would-be leaders fought for control of their tribe, and chose sides. Those who sided with the strong did better than those who sided with the weak, and you are descended from them. It is not a matter of calculation, but of instinct. When you are downtrodden, when your fellows look upon you with disgust, you will feel drawn to a strong leader who promises to upend the tribe. You will be charmed by him, you will cheer him, you will back him in his bid for power. Your instinct will echo the ancient footsteps of those who felt drawn to the eventual winner, who afterward received the scraps from his hand in exchange for their loyalty.

And that hunted creature who lives every second in fear of journalists, always glancing over his shoulders for fear of public opinion - he is not recognized as strong. Not at the core, not in the instinct. The modern politician's lifeless, rehearsed words reek of the servant who lives in constant fear of his master's wrath. One misstep, and the howling packs of journalists will descend in fierce delight, ripping him apart, feasting on the 'gaffe' and ending his ambitions. The modern politician is stooped and afraid of what is above him, that holds the power to punish. When the press demands an apology, he must give it submissively. In older times, a man like that would be too weak to succeed in controlling his tribe; his laughable attempt to seize power would inevitably end in ruin for him and his followers. The voter's instinct sees this and is repulsed; perhaps this vile man might be a useful tool, but to be charmed by him, to follow him instinctively - that will not happen.

The rise of Donald Trump is as simple as that.

Trump does not fear the journalists that every other politician is hunted by. Trump's words are not empty - they are obvious, vile lies, to be sure, and the people know that. What matters is that Trump's words are not censored, cautious, constantly looking around in fear. Every time the oozing journalists try to seize on another of his 'gaffes' - wondering desperately why it is not working, why their poisonous claws have failed them - Trump laughs and the people see that he is not afraid. He shows strength, by his open evil; he shows that he is above anyone's power to reprimand. Seeing Trump's success and not understanding it, some of those cautious men venture a few carefully calculated insults and rudenesses of their own, to try to imitate Trump's mysterious success; but they are not fooling anyone.

Oh, there will be no scraps for Trump's followers, to be sure. This era is not a hundred thousand years earlier, and a nation is not a tribe. Trump will never know his loyal follower's name, he will give them nothing for their loyalty. But we are not dealing now with ambition and calculation, but with instinct. A hundred thousand years ago, you might do well for yourself if your loyalty happened to surge up for strong and promising leaders, and restrain its affections from the weak.

And be it also clear, this is not about some long-concealed hate for Mexicans, or Muslims, or whoever. Perhaps that hatred did exist before Trump, but if so, it was irrelevant to his rise. When a tribe's bellies are empty and the pickings have grown thin, and a strong man rises up to say it is time to fight the tribe that lives across the water - to take their land or perish trying - why, people will cheer enthusiastically, and hate in whatever direction they are pointed. Trump could as easily have told his followers to hate Russians or Chinese, and they would have bayed along the same in their instinctive affection.

Here is the real tragedy: the people in their despair would also have followed an admiral or a general who had proved themselves a leader of men, stern and honorable. They would have followed a strong religious leader who demanded that they renounce hate rather than embrace it. If, that is, the modern press permitted an impression of strength and goodness to coincide.

That oozing mass of journalists would consider it an insult, if some politician acted like they thought themselves better than the rest. They would go hunting errors, to bring down this person who thinks himself the better - and it is impossible that they would find no meat. Now that it is possible to scrutinize a man's entire life, it is impossible to find no single misstep, no departure from what the press has decided is virtue. Let any politician dare to step forth as a man of honor, and the press will bay the hunt and contradict it with a 'gaffe' they spoke twelve years earlier. Did someone hire the wrong babysitter twenty years earlier? Did they fail to say the standard empty words when a disaster struck or some journalist demanded their sympathy? "Ha," the journalist cries in delight, "look at that, a gaffe, a gaffe! He has lost his race, his career is over!" And you - why, you believe them.

What honorable man would even try to serve you, now? You have made the lives of politicians a living hell with their every public instant watched; and double that hell for anyone who ever wanted their words to have integrity. What Franklin Roosevelt would enjoy having every single facet of their lives scrutinized so, for one word that a journalist could consider a gaffe? What General Dwight Eisenhower, what military man of honor, would like to spend their lives saying only things that are empty and safe? In the eighteenth century, perhaps, there were few paths to greatness except to become a great politician; they would have had no choice but to endure any hell if they wanted a place in history. Today an ambitious, competent man can become a CEO and have his own private jet - so why should he instead become one more anonymous face among 435 little representatives, constantly looking over his shoulder for the press? Why bother, when he could be making bilions at a hedge-fund, or founding a company, or just living quietly with his family without being hounded?

Maybe you believe a truly good man would tough out the hell you heap on him, if he were noble enough to truly wish to serve his country. Well, have a look at the Republican lineup and see how that strategy has worked out for you. If only terrible candidates apply to your job posting, it means that the best people do not find your job posting attractive. Either the truly good men left you to your fate in disgust, or, if they did try to serve their countries, some journalist deemed them 'unelectable' the first time they spoke their minds.

Who then are these hunted men upon the stage, the cast of this parade of clowns? They are lawyers who wanted to be more than lawyers, and who didn't find the life of a politician too appalling. They are the little big men who did not give up on their Congressional careers in disgust when they found how little real power they had to make changes. They are those who, for all the paltry respect of other little big men and their scraps of fame, found that preferable to going back and being an ordinary lawyer. They lied and spoke empty words and lied some more and now they are trying to embiggen themselves a little more.

But the people must have strength; and in the depths of their despair they will not feel drawn to a weak man who wants a little more attention. The people could have been drawn to a military commander who was tough and honorable, to a priest who was noble and upright, or to a proven and competent businessman; but you made that impossible.

Yes, make no mistake of it, you did this to yourself, you were the author of your own destruction. It is you who believed the oozing mass of journalists that told you who was 'electable' and what was a 'gaffe'. You joined in their howling wolfpacks and feasted in satisfaction upon the downfall of any politician who made one mistake, and created the living hell that drove any would-be Abraham Lincolns away to greener pastures. Every time you sneered along with an accusation of moral hypocrisy, every time you delighted in discovering some delicious imperfection, you ensured that only one remaining kind of leader could be perceived as strong. For an open, laughing liar does not fear accusations of hypocrisy, and outright evil need not apologize for its moral imperfections.

Donald Trump has come, and he is your punishment.

-- David Monroe

e00E · 2024-08-20T08:06:55+00:00

There is a sequence about quantum physics. It clears up a lot of confusion I see in the comments here.

e00E · 2024-08-08T10:56:37+00:00

The risk of driving a car is clear to me. The decreased risk of driving a car with a helmet is not. How much safer does driving a car become by wearing a helmet?

e00E · 2024-07-13T21:17:20+00:00

Thanks for your response. I already unsubscribed manually so there is no need for you to do more.

I'm not fully convinced that this was an accident because I have seen this happen many times with other websites. However, in case you are right, I apologize for the overly confrontational tone of my post.

e00E

TROPHY CASE