Duktape VS V7

Im my projects I search for single file libs.(like https://github.com/svaarala/duktape etc...)

Use lrand48(), or better, implement a high-quality RNG like PCG or splitmix64.

You can also refer to the Unicode routines of other small JS engines[1,2], those don’t use ICU either, although the implementations are mercilessly size-optimized (to put it politely) and restricted to what the target JS version requires (e.g. casemapping but no normalization).

[1] https://github.com/bellard/quickjs/blob/master/libunicode.c

[2] https://github.com/svaarala/duktape/blob/master/src-input/du...

> memcpy from bytes to a NaN should work fine

Signaling NaNs are explicitly undefined in C11 F.2.1.: "This specification does not define the behavior of signaling NaNs." - and in practice may be "quieted" by conversion to Quiet NaNs, changing their bit patterns. Fast math optimization flags will also break the hell out of your code by assuming NaNs are impossible. I want to say there are more circumstances where optimizers and compiler generated code can butcher your NaN payloads, but I'd be working off recollected hearsay and I can't find a source, so don't quote me on that.

NaN boxing is common enough that, if you take the right precautions, a modern compiler should probably support it, maybe. NaN boxing is uncommon enough that, if your codebase needs to be sufficiently portable, you need an opt out for when it breaks. Let's review duktape's scars:

https://github.com/svaarala/duktape/blob/123d9426d5e5b36d5da...

https://github.com/svaarala/duktape/blob/5252b7a50611a3cb8bf...

https://github.com/svaarala/duktape/blob/224a0b89ca08a36e37e...

Note that "the right precautions" involve unions and proper integer types to avoid optimizer-invoked rewrites of the value and debugging when things go wrong, not simply YOLOing bytes into a double via memcpy. Note that debugging when it all goes terribly wrong can be quite painful. I've personally had the misfortune of being forced to debug duktape being built with fast math optimizatoins enabled on one "rare" platform + build configuration that wasn't caught by duktape's #if defined(__FAST_MATH__) checks linked above (wasn't Clang nor GCC, so go figure it didn't make the same #define)

I was expecting this to be about Duktape <https://github.com/svaarala/duktape>, but heh, for sure no. I'd bet $1 there's no way youtube-dl would switch, but I wonder if yt-dlp would?

Fast math optimizations can break code like this by breaking isNaN.

I was porting a C++ project to a certain platform - and that platform enabled a -ffast-math equivalent by default in Release (but not Debug) builds! This broke duktape, a JS engine said project embedded, in some nasty and subtle ways. Instead of storing a number/pointer/??? (8 bytes) + type tag (4? bytes) for each dynamically typed JS value, duktape can bit-pack values into a single 8 byte "double" value by storing object/string handles as NaN values - this isn't an uncommon trick for dynamically typed scripting stuff:

https://github.com/svaarala/duktape/blob/c3722054ea4a4e50f48...

Naturally, the -ffast-math equivalent broke isNaN checks, which caused random object/string handles to be mistakenly reinterpreted as "numbers" - but only in Release builds, for this one particular platform, in one rarely taken branch, so neither QA nor CI caught it, leading to hours of manufacturing a repro case, stepping through an absurd amount of code, and then finally looking at the default build rules and facepalming.

Cursing the platform vendor under my breath, I overrode the defaults to align with the defaults of every other config x platform combination we already had: no fast math. If you want those optimizations, use SSE-friendly NaN-avoiding intrinsics - or, if you must use the compiler flags, ensure you do so consistently across build configs and platforms, perhaps limited to a few TUs or modules if possible. This allows you to have a chance at using your Debug builds to debug the resulting "optimizations".

Sure. For example, DukTape is an implementation of Javascript designed to be embedded in other projects. Google's V8 Javascript engine (used in Chrome), can also be embedded, see Node.Js for example.

- Duktape (4.8k stars)

I used such a succinct AST structure to implement a JavaScript parser and interpreter for a severely memory constrained environment (embedded): V7 (https://github.com/cesanta/v7)

We later switched to a ast->bytecode compilation step but for a while the implicit AST was directly traversed during interpretation.

Nice! A few years ago I took a stab at this problem space with https://github.com/cesanta/v7 ; with fun tricks like in-place compacting GC, stdlib JS object graph "frozen" in rom etc

https://github.com/cesanta/v7

Languages are not all equal nor do they all function in the same way, and that's not my opinion.

Javascript syntax itself is one thing, and you can certainly feel free to Javascriptify some C++ libraries and make it all look a certain way for specific tasks, while managing things behind the scenes, up to a point... but there is no getting around the fact that SOMEONE and some languages are needed to implement low level systems functionality.

the power of Cython or the Python C FFI is that it allows you to script/glue modular native code.

You then state "C++14 may have been ratified 7 years ago but it's not the target code your build chain spits out"

no, a C++ COMPILER spits out assembler code that then gets assembled and linked into an executable.

The C++ or C code corresponds directly to a given set of assembler instructions which correspond directly to CPU instructions.

You claim that Python programming of microcontrollers is mainstream, but this is not true nor possible. Python SCRIPTING of code modules (that cannot be written in Python) is certainly one way to assemble a system from pre-built legos.

If you refer to knowing what I'm talking about as gatekeeping and egoism, might I suggest that you insist less forcefully in the correctness of incorrect things you state? we could be done with this spat in short order if YOU would refrain from speaking falsehoods. lies.untrue things.

I look forward to your lisp c compiler. make sure that it's 100% lisp from the bottom up, or I'll consider you're having ceded my point. Consider that the lisp you author in has a garbage collection system that lisp cannot have written originally, nor has any semantics for the underlying memory structures of, but hey, I guess if one is committed to pretending that all languages are equal for all tasks, who am I to question ones self-identification with a given language.