Hacker News: stassats

New comment by stassats in "Cl-kawa: Scheme on Java on Common Lisp"

stassats — Wed, 25 Feb 2026 14:56:15 +0000

I did that to write simd routines for sbcl: https://github.com/sbcl/sbcl/blob/master/src/code/arm64-simd... Probably the best way of writing assembly, can evaluate the function immediately, use macros and any other code to emit instructions, even can print register values (instruction-level stepping would be even better, but too much work).

New comment by stassats in "Steel Bank Common Lisp"

stassats — Wed, 25 Feb 2026 14:28:35 +0000

Still 40 years to go.

New comment by stassats in "Steel Bank Common Lisp"

stassats — Wed, 25 Feb 2026 14:28:02 +0000

I have also seen some outright crashes on the new GC.

New comment by stassats in "Addressing the adding situation"

stassats — Tue, 02 Dec 2025 20:54:23 +0000

The tricks to avoid multiplication (and division) are probably worth a whole post.

  x * 6:
  lea eax, [rdi+rdi*2]
  add eax, eax

  x * 7:
  lea eax, [0+rdi*8]
  sub eax, edi
  
  x * 11:
  lea eax, [rdi+rdi*4]
  lea eax, [rdi+rax*2]

But with -Os you get imul eax, edi, 6

And on modern CPUs multiplication might not be actually all that slow (but there may be fewer multiply units).

New comment by stassats in "Addressing the adding situation"

stassats — Tue, 02 Dec 2025 14:53:27 +0000

The text mentions that it can also do multiplication but doesn't expand on that.

E.g. for x * 5 gcc issues lea eax, [rdi+rdi*4].

New comment by stassats in "ECL Runs Maxima in a Browser"

stassats — Mon, 03 Nov 2025 10:24:42 +0000

ABCL is really slow.

New comment by stassats in "Finding and Understanding Bugs in C Compilers (2011) [pdf]"

stassats — Wed, 01 Oct 2025 00:18:45 +0000

A good strategy if you don't care about fixing bugs.

New comment by stassats in "Walking around the compiler"

stassats — Fri, 26 Sep 2025 14:59:19 +0000

That shouldn't mean that it doesn't return a NaN. Things are generally not optimized away because of NaNs. E.g. in GCC, abs(c) > -1.0 is not folded, unless building with -ffast-math

New comment by stassats in "Walking around the compiler"

stassats — Fri, 26 Sep 2025 12:08:32 +0000

That fix has limited applicability. x * x is also a non-negative float. But abs(x * x) is not optimized. Or abs(abs(x)+1). GCC, for example, does know that.

New comment by stassats in "Quirks of Common Lisp Types"

stassats — Tue, 02 Sep 2025 23:10:39 +0000

(+ 2 (id "2")) may also produce a compile time warning. Nothing precludes from having a special rule for that. Like (+ 2 (print "2")) does warn.

New comment by stassats in "Ask HN: What toolchains are people using for desktop app development in 2025?"

stassats — Sun, 10 Aug 2025 17:09:29 +0000

> changes in the Qt project made the technique used by the Qt4 bindings impractical for Qt5 or Qt6 - at least that was my understanding when I looked into it.

It was hard to do reasonably with qt4 already. The best solution would be to support the C++ ABI natively, but that's never going to happen.

New comment by stassats in "Notes on Graham's ANSI Common Lisp (2024)"

stassats — Mon, 14 Jul 2025 14:46:00 +0000

> Why does SBCL not use LLVM?

Why doesn't GCC use LLVM? Why is Zig writing their own backend?

New comment by stassats in "Web Embeddable Common Lisp"

stassats — Wed, 25 Jun 2025 21:55:28 +0000

> lack of tail-call elimination

But lisp doesn't need TCO.

New comment by stassats in "Beware of Fast-Math"

stassats — Sat, 31 May 2025 10:45:23 +0000

You can turn them back into rationals, (rational (sqrt 2d0)) => 6369051672525773/4503599627370496

Or write your own operations that compute to the precision you want.

New comment by stassats in "A Common Lisp jq replacement"

stassats — Fri, 02 May 2025 13:35:48 +0000

>(safety 0)

Please, don't do that!

New comment by stassats in "Depending in Common Lisp – Using the CLOS dependent maintenance protocol (2022)"

stassats — Sat, 01 Mar 2025 21:24:21 +0000

>any system that relies on information that was typed into a REPL three-months ago and is now only stored in the binary state of that REPL and nowhere else is totally insane as a production product.

Nobody does that.

New comment by stassats in "Nvidia's Project Digits is a 'personal AI supercomputer'"

stassats — Tue, 07 Jan 2025 20:34:59 +0000

> roadrunner is petaflops of FP32

Isn't it actually FP64?

New comment by stassats in "The Alder Lake SHLX Anomaly"

stassats — Fri, 03 Jan 2025 18:01:16 +0000

Using EAX is one byte shorter, so it might be doing that inadvertently.

New comment by stassats in "Mark–Scavenge: Waiting for Trash to Take Itself Out"

stassats — Tue, 26 Nov 2024 04:01:01 +0000

Common Lisp. The dynamic-extent declaration allows for stack allocation.

New comment by stassats in "Bit-twiddling optimizations in Zed's Rope"

stassats — Wed, 20 Nov 2024 23:59:04 +0000

> because 64-bit ARMv8.0 lacks a POPCNT instruction

It does have this: https://developer.arm.com/documentation/ddi0596/2021-09/SIMD...

And GCC happily uses it https://godbolt.org/z/dTW46f9Kf