vyodaiken

14 ms·

91.
by vyodaiken 7y ago
It's super simple. You have a network where sometimes messages don't get delivered. One agent (process, site ... ) sends a message m to a collection of other agents distributed around the network. How can the sender be sure that
92.
by vyodaiken 7y ago
I wrote a little simulation. Paxos rarely gets stuck with a small number of proposers/acceptors, but jams up solid once you get to, I forget, 10 or 20. Here it is: https://www.yodaiken.com/wp-content/uploads/2
93.
by vyodaiken 7y ago
Paxos livelocks (doesn’t work). So Lamport suggests electing a coordinator via timeouts(since flp is a joke). But if you can elect via timeouts you don’t need paxos at all. QED The really annoying thing is that "Paxos Made Simple&quot
94.
by vyodaiken 7y ago
Paxos is wrong, as Lamport explains on page 7 of "Paxos made simple", but apparently nobody reads that far.
95.
by vyodaiken 8y ago
great
96.
by vyodaiken 8y ago
That's nice. So when the Zetas take your land, it's all good?
97.
by vyodaiken 8y ago
So right to property means I can burn tires on "my" land and pour benzene into the water table? And property titles are maintained by magic pixies and enforced by private police? And I love the idea that crying fire in a theater i
98.
by vyodaiken 8y ago
Even the C standard still pays lip service to the notion of C as high level assembler. The notion that C should be an abstract high level language insulated from the machine is foreign both to the language design and usage. C is not design
99.
by vyodaiken 8y ago
I can't imagine it is ever the intent of the programmer that if(i+1 < i)x be there simply as decoration to be removed by the compiler. If the compiler can deduce that the test will evaluate as false (or true), it is perfectly reason
100.
by vyodaiken 8y ago
Why do you assume we want either Pascal ("wrapping semantics") or random-"optimizations". Those are not the choices. It's actually very easy for the compiler to detect that it is a check to avoid overflow, it's
101.
by vyodaiken 8y ago
>OK, then that definition excludes register allocation as a permitted optimization Oh come on.
102.
by vyodaiken 8y ago
But the purported massive difference of the video disappears on those versions too. So that's the big proof of the efficacy of UB driven "optimization" - one additional assembler instruction in the clang code, some movslq vs
103.
by vyodaiken 8y ago
>The point of giving that example is to show that there are studies that examine the benefit of undefined behavior, Of course, that is exactly what Regehr's paper does not show. It shows that a modification of Clang/LVM UB oper
104.
by vyodaiken 8y ago
-fwrapv gives you the desired C semantics.
105.
by vyodaiken 8y ago
That's correct, but I fault the Standard committee for not rejecting the peculiar interpretation that allows Compiler developers to assume e.g. overflow does not happen while emitting code that does overflow.
106.
by vyodaiken 8y ago
You are joking, right? Regehr's paper covers a proposed CHANGE to Clang/LVM UB behavior, while I was asking for studies that show advantages of UB "optimization" itself. The numbers show minor changes of performance on a
107.
by vyodaiken 8y ago
Do you have a single published study showing that the UB "optimizations" benefit real programs? I typed in the example code and current Clang generates exactly the same assembly for both u and not u integers - which is correct. So
108.
by vyodaiken 8y ago
Wait a second: both ARM and IA-64 have 32 bit operations.
109.
by vyodaiken 8y ago
Again: not a single study with a benchmark, just an anecdote that actually means the opposite of what is intended. The authors of Bzip had to write non-idiomatic code to prevent UB "optimization" from breaking their code, and thi
110.
by vyodaiken 8y ago
The rule allows both the union trick and a totally hacky char type exception (this was added because the standards authors found out that their rule was inconsistent and instead of backing it out, tried to hack it up). 7 An object shall hav
111.
by vyodaiken 8y ago
There is no practical use for those UB "optimizations".
112.
by vyodaiken 8y ago
Just a reminder that there are ZERO published studies showing that these UB "optimizations" have significant value for any real programs. They impose a bizarre notion of C semantics that is not compatible with the language design.
113.
According to Clang C, -2147483648 is sometimes not negative(yodaiken.com)
3 points by vyodaiken 8y ago|0 comments
114.
by vyodaiken 8y ago
absence of an example device is a strong strike against the Bloomberg article.
115.
by vyodaiken 8y ago
That seems entirely circular.
116.
by vyodaiken 8y ago
You're missing my point.
117.
by vyodaiken 8y ago
>Again, it seems unlikely that this was the sticking point. Look at the proof - page after page of work showing how to encode and decode formal propositions using primitive recursive functions. >E.g. Hilbert understood mathematics as
118.
by vyodaiken 8y ago
What made the theorem hard is not the details, which are simple, it's the conceptual leap to thinking about mathematical statements as mathematical objects - something that is much easier for us than for mathematicians of Godel's
119.
by vyodaiken 8y ago
no "self" in C.
120.
by vyodaiken 8y ago
There is no connection between Ayn Rand and pragmatism.

More ›