Viewing profile — purplesyringa

To expand on this, the imprecision arises the moment you write 0.1 (decimal) in source code and the compiler converts it to binary; the arithmetic itself is (mostly) exact. So as l…

`log_a x The topic of the post is that in PHP and Lua (without LuaJIT), sometimes this inequality doesn't hold, and instead we get `log_a x > log_b x`, which is very incorrect and …

I sort of needed to do that. I needed to compress data with an approximately geometric distribution, and as part of that process I needed to invert its CDF, which is `CDF = 1 - (1 …

That's interesting! On my PC it reproduces under Lua 5.5 (`log_a x > log_b x`), but not under LuaJIT (`log_a x = log_b x`). I took a look at LuaJIT's implementation ( https://githu…

Thank you! This point has been driving me mad for the last couple of years. While answering a sibling comment, I found a paper analyzing various libms for their precision: https://…

Thank you! I completely agree with this, floats are treated as a lot more magical than they actually are. I myself often rely on their exact guarantees for fun tricks (e.g. fast pr…

The log base is a parameter, not a function, so that doesn't typecheck. Multivariate monotonicity isn't really a popular term, as far as I'm aware, so I'm not aware of good termino…

Python, PHP, and Rust do indeed use libm. Not LLVM's libm specifically, though, but rather just about anything they can find in runtime, and those libraries can have suboptimal acc…

> PHP uses a JIT from Lua. Wow, TIL! I was certain this is a mistake, but apparently PHP uses DynAsm ( https://wiki.php.net/rfc/jit ), which was developed for LuaJIT ( https://luaj…

Yeah, I simplified it a little. Though I must say I'm surprised pretty much every library I looked at uses the natural logarithm specifically, and not log2, which would seemingly b…

> small source files How small are we talking? We've had great success with bzip-style compression on ~400 KB (about 20% better than gzip), but I don't know if it scales well. It's…

We considered it, but that requires knowing the path to the file and being able to open it, which I don't think is possible in general (e.g. if the file is loaded with `loadstring`…

Thanks! I relayed this to Yuki and we'll make sure to fix the issues. > You can include the start delimiter in the string: At first I had no clue why we thought that didn't work, i…

> the fence basically means "resolve all funny business with this variable before proceeding" Thanks, that's a good explanation! I understand it better now. > What I'd actually wor…

> A huge part of the problem here is that you're playing with the 8-bit registers. [...] That's an interesting thought, though in this particular case I think it's a little misguid…

The right-shift is the problem. You need to shift right by `j * 8`, which itself requires a shift to compute (`j better than a load, but it's still noticeable.

I knew the loop was latency-bound and I couldn't easily decrease the latency, so I knew I had to somehow avoid the dependency chain at all. I remembered that CPUs predict some prop…

The optimization in the post is only advantageous if `next_j[i][j] == j` holds often enough. Without prior knowledge, the compiler can't know if it's going to improve performance, …

That would be great, if only it worked as intended! From the perspective of an optimizing compiler, `a == b ? a : b` is worse than `b` regardless of the probability you assign to `…

Thanks!

My brain does not understand how one can see `(+ a b)` in text and read it as `a b +`. I suppose you can argue that moving operators to the right and removing all parentheses conve…

There used to be hype about Wasm, now it's a technology as any other. It's still used, and used a lot; it just doesn't get focused on as much.

> tl;dr: the LISP syntax is just syntax sugar. The textual format is as "stack-like" as the binary format. Not that you're technically wrong, but I think you're begging the questio…

There's just so many "but"s to this that I can't in good faith recommend people to treat floats as deterministic, even though I'd very much love to do so (and I make such assumptio…

And here are the constants for the ostensibly more useful 54x54->108 product: https://play.rust-lang.org/?version=stable&mode=release&edit... I tried to go even higher, but the bou…