alt.hn

2/7/2026 at 5:39:53 PM

SectorC: A C Compiler in 512 bytes (2023)

 https://xorvoid.com/sectorc.html

by valyala

2/8/2026 at 12:06:25 AM

If this implementation had existed in the 1980s, the C standard would have a rule that different tokens hashing to the same 16-bit value invoke undefined behavior, and optimizing compilers in the 2000s would simply optimize such tokens away to a no-op. ;)

by layer8

2/8/2026 at 3:53:15 AM

"you don't have -wTokenHashCollision enabled! it's your own foolish ignorance that triggered UB; the spec is perfectly clear!"

by RodgerTheGreat

2/8/2026 at 1:38:17 PM

Hey stop it with the ad hominems!

by fredrikholm

2/8/2026 at 12:37:23 AM

Too real! LMAO

by xorvoid

2/7/2026 at 8:56:27 PM

Oh, it looks like my X86-16 boot sector C compiler that I made recently [1]. Writing boot sector games has a nostalgic magic to it, when programming was actually fun and showed off your skills. It's a shame that the AI era has terribly devalued these projects.

[1] https://github.com/Mati365/ts-c-compiler

by mati365

2/8/2026 at 11:35:59 AM

Er, what? The article describes a compiler for a not-quite-C programming language which fits entirely in 512B. Your project, if I see this correctly, can optionally produce code meant to execute as boot sector.

Both interesting projects, but other than the words 'boot sector', 'C' and 'compiler', I don't see a similarity.

by guenthert

2/8/2026 at 5:50:08 AM

> when programming was actually fun and showed off your skills

Oh no. Now more people are able to do what I do. I'm not special anymore.

by w4yai

2/8/2026 at 6:03:32 AM

Seems like this is facetious but to me, “I’m not special” is a pretty valid thing to be sad about.

by mlsu

2/8/2026 at 7:30:24 AM

The two dos in "do what I do" do absolutely not carry the same meaning.

by tgv

2/7/2026 at 8:12:39 PM

I may be the author.. enjoy! It was an absolute blast making this!

by xorvoid

2/7/2026 at 8:47:01 PM

An interesting use case - for the compiler as-is or for the essentiall idea of barely-C - might be in bootstrapping chains, i.e. starting from tiny platform-specific binaries one could verify the disassembly of, and gradually building more complex tools, interpreters, and compiler, so that eventually you get to something like a version of GCC and can then build an entire OS distribution.

Examples:

https://github.com/cosinusoidally/mishmashvm/

and https://github.com/cosinusoidally/tcc_bootstrap_alt/

by einpoklum

2/7/2026 at 9:00:02 PM

It would be interesting to understand what non-toy programs can be coded in this subset of C. For example, could tcc be rewritten in this dialect?

by teo_zero

2/7/2026 at 8:20:15 PM

This is very nice. I'm currently writing a minimalist C compiler although my goal isn't fitting in a boot sector, it's more targeted at 8-bit systems with a lot more room than that.

This is a great demonstration of how simple the bare bones of C are, which I think is one reason I and many others find it so appealing despite how Spartan it is. C really evolved from B which was a demake of Fortran, if Ken Thompson is to be trusted.

by veltas

2/7/2026 at 8:44:20 PM

Would and how much would it shrink when if, while, and for were replaced by the simple goto routine? (after all, in assembly there is only jmp and no other fancy jump instruction (I assume) ).

And PS, it's "chose your own adventure". :-) I love minimalism.

by JamesTRexx

2/7/2026 at 9:29:22 PM

What fancy jumps are present in assembly depends on the CPU architecture. But there are always conditional jumps, like JNZ that jumps if the Zero flag isn't set.

by SAI_Peregrinus

2/8/2026 at 9:14:46 AM

The “fancy jump” is the branch instruction. As far as I know all ISAs have them. Even rv32i which is famously minimal has several branch instructions in addition to two forms of unconditional jump. Branches are typically used to construct if / for / while as well as && and || (because of short circuiting) and ternary (although some architectures may have special instructions for that that may or may not be faster than branches depending on the exact model). Without it you would have to use computed goto with a destination address computed without conditional execution using constant time techniques.

by MobiusHorizons

2/8/2026 at 1:03:16 AM

It only does if & while, not for. A goto in a single-pass thing would need separate handling for forwards vs backwards jumps, which involves keeping track of data per name (in a form where you can tell when it's not yet set; whereas if/while data is freely held in recursion stack). And you'd still need to handle at least `if ( expr ) goto foo;` to do any conditionals at all.

by dzaima

2/8/2026 at 1:01:10 AM

It's "choose your own adventure"

by direwolf20

2/8/2026 at 1:39:27 AM

thats the most important thing i noticed about the article, apart from the forth tokenising ideas.

by globalnode

2/8/2026 at 10:33:12 AM

This is the kind of project that reminds you how far removed modern development is from the actual machine. We pile abstractions on abstractions until "Hello World" needs 200MB of node_modules, and then someone fits a C compiler in 512 bytes.

Not saying we should all write boot sector code, but reading through projects like this is genuinely humbling. Great educational resource too.

by wzbtoolbox

2/8/2026 at 5:29:21 PM

This kind of comment reminds me of how broad "software development" is.

On other HN posts, they're stating something like "software development is dead", "LLM as a compiler", "Do you read compiled assembly?", and so on.

While some other posts like this contain huge mechanical sympathy and literally r/w the assembly directly.

by lock1

2/7/2026 at 8:56:27 PM

Compare that to the C compiler in 100,000 lines written by Claude in two weeks for $20,000 (I think was posted on HN just yesterday)

by mojuba

2/7/2026 at 9:31:09 PM

It's a fun comparison, but with the notable difference that that one can compile the Linux kernel and generate code for multiple different architectures, while this one can only compile a small proportion of valid C. It's a great project, but it's not so much a C compiler, as a compiler for a subset of C that allows all programs this compiler can compile to also be compiled by an actual C compiler, but not vice versa.

by vidarh

2/7/2026 at 10:15:35 PM

But can it compile "Hello, World" example from its own README.md?

https://github.com/anthropics/claudes-c-compiler/issues/1

by d_silin

2/7/2026 at 10:23:18 PM

It's fascinating how few people read past the issue title

by Retr0id

2/8/2026 at 2:26:23 AM

And this is exactly why coding with AI is not-so-slowly taking over.

Most people think they are more capable than they actually are.

by fooker

2/7/2026 at 10:24:20 PM

Noticed the part where all it requires is to actually have the headers in the right location?

by vidarh

2/7/2026 at 10:27:39 PM

"The location of Standard C headers do not need to be supplied to a conformant compiler."

From https://news.ycombinator.com/item?id=46920922 discussion.

by d_silin

2/7/2026 at 10:43:07 PM

And it doesn't for the compiler in question either. As long as the headers exist in the places it looks for them. No compiler magically knows where the headers are if you haven't placed them in the right location

by vidarh

2/7/2026 at 11:15:34 PM

stddef.h (et al) should be shipped by the compiler itself, and so it should know where it is. But they rely on gcc for it, hence it doesn't always know where to look. Seems totally fine for a prototype.

by Retr0id

2/7/2026 at 11:39:13 PM

Especially given they're not shipping anything. The GCC binaries can't find misplaced or not installed headers either.

by vidarh

2/8/2026 at 6:58:07 PM

Shipping GPL headers that explicitly state that they are part of GCC with a creative commons licensed compiler would probably make a lot of people rather unhappy, possibly even lawyers.

by josefx

2/7/2026 at 11:20:53 PM

Would you accept the same quality of implementation from a human team?

by d_silin

2/8/2026 at 1:11:18 AM

I've certainly encountered clang & gcc not finding or just not having header files a good couple times. Mostly around cross-compilation, but there was a period of time for which clang++ just completely failed to find any C++ headers on my system.

by dzaima

2/8/2026 at 2:25:25 AM

Yes, clang is famously in this category.

If you copy the clang binary to a random place in your filesystem, it will fail to compile programs that include standard headers.

by fooker

2/7/2026 at 11:37:16 PM

A compiler that can't magically know how to find headers that don't exist in the expected directory?

Yes, that is the case for pretty much every compiler. I suppose you could build the headers into the binary, but nobody does that.

by vidarh

2/8/2026 at 1:41:48 AM

Consider: content-addressed headers.

by tekne

2/8/2026 at 12:04:59 PM

Then you might as well embed the headers, since in that case you can't update the compiler and headers separately anyway.

by vidarh

2/8/2026 at 10:21:31 AM

Noticed the part where the exact instructions from the Readme were followed and it didn't work?

by HendrikHensen

2/8/2026 at 11:18:00 AM

So we're down to a missing or unclear description of a dependency in a README - note following the instructions worked for others -, from implications the compiler didn't work.

by vidarh

2/8/2026 at 1:24:53 AM

Well I'm pretty sure the author can make a compliant C compiler in a few more sectors.

by mojuba

2/8/2026 at 3:11:32 PM

I mean we know it can be done in little space, given the many tiny C compilers. I think what is most interesting about this one is exactly the creative shortcuts. It's an interesting design space for e.g. bootstrapping to impose extra restrictions.

by vidarh

2/7/2026 at 8:09:04 PM

The way hashing is used for tokens and for making a pseudo symbol table is such an elegant idea.

by sanufar

2/7/2026 at 8:48:48 PM

I think the same. Really nice project and good trick with hashing tokens.

PS. There left 21 bytes (21 * 0x00 - from 0x01e0 to 0x01fd). Maybe something can be packed there ;)

by fix4fun

2/8/2026 at 10:03:19 AM

I actually "shipped" a parser using the symbols' hash(as the only identifier) for a test tool once. Hopefully, the users never used enough symbols to collide 32-bits.

by avadodin

2/8/2026 at 3:03:48 PM

I've had the idea before. Was never quite brave enough to do it. It's elegant until it isn't....

by benj111

2/8/2026 at 9:08:33 AM

Such a great read! Reminds me of the bootsector OS I made some time ago[^1]

Maybe it's time to equip it with a C compiler...

[1]: https://github.com/shikaan/osle

by shikaan

2/8/2026 at 2:34:12 AM

This is so cool!

Fun fact, Tiny C Compiler was derived from such a C compiler submitted to the the International Obfuscated C Code Contest.

https://www.ioccc.org/2001/bellard/index.html

by fooker

2/8/2026 at 5:53:04 AM

Meh, I did an entire awk interpreter in two lines:

  #!/bin/sh
  echo "awk: bailing out" >&2

by pseudohadamard

2/8/2026 at 7:46:54 AM

For me is not interesting because it fits in 512 bytes, it's interesting because it's very simple. I think it would be a great introduction to learning about compilers.

by DeathArrow

2/8/2026 at 5:17:42 AM

There seems to be a good amount of interest for a boot sector compiler!!

If you're running on Linux, adjust the qemu call to use alsa rather than coreaudio.

I generated a pull request for this on Github. If the author is happy enough with my verbose shell scripting style :-) it might get included.

by kreelman

2/8/2026 at 4:08:50 AM

C-subset, to be precise; but microcomputer C compilers were in the tens of KB range, for one that can actually compile real C.

by userbinator

2/8/2026 at 8:04:04 PM

Brilliant! I love the stealing of Forth ideas to power this. Forth’s minimalism is highly underrated.

by drob518

2/8/2026 at 9:43:21 AM

> Big Insight #2 is that atoi() behaves as a (bad) hash function on ordinary text. It consumes characters and updates a 16-bit integer.

I could have sworn I remembered atoi() being defined to return 0 for invalid input (i.e. text not representing an integer in base ten).

by zahlman

2/8/2026 at 4:43:04 PM

That would be true of one using a libc, but in a boot sector, you only have the bios, so the atoi being referenced is the one defined in c near the beginning of the article

by MobiusHorizons

2/8/2026 at 6:32:32 PM

Ah, I somehow skipped over that exact code block on first read.

by zahlman

2/8/2026 at 7:33:37 PM

This is really beautiful (I feel like this sort of project is outsider art), thank you for sharing.

by alittlebee

2/8/2026 at 6:17:07 PM

Great read. It would be neat to see a mini operating system under 1 kb of code.

by hgs3

2/7/2026 at 9:22:43 PM

Why is it called a C Compiler if it's a subset of C?

by SeanSullivan86

2/8/2026 at 8:01:01 AM

[flagged]

by userbinator

2/8/2026 at 11:56:06 AM

Why is your visceral reaction is to frame it as a quest for truth versus a great suppression of truth? Everything alright up there?

Literal second sentence in the article, in case it wasn't incredibly obvious to people anyways:

> It supports a subset of C that is large enough to write real and interesting programs.

I'm all for more boring headlines, but this characterization is ridiculous.

by perching_aix

2/8/2026 at 8:42:09 PM

I've had enough of headlines that overpromise and underdeliver. It's essentially false advertising. It's not like the word "subset" would put it over the length limit.

by userbinator

2/7/2026 at 8:47:29 PM

> I wrote a fairly straight-forward and minimalist lexer and it took >150 lines of C code

was it supposed to be "<150"?

by NooneAtAll3

2/7/2026 at 9:01:54 PM

They're saying the naive implementation was more than 150 lines of C code (300-450 bytes), i.e. too big.

by owalt

2/8/2026 at 5:28:36 AM

Nice, now you can dd it to your boot sector and ... Wait, it is 2026, there are 1000 ways of booting and memory mapping on so-called unified ARM architecture @,@

by wbsun

2/7/2026 at 9:40:20 PM

Lacking support for structs, I think this is too minimalistic to be called "a C compiler".

by gonzus

2/8/2026 at 3:10:29 PM

Weren't structs a fairly late addition to C?

And anyway, isn't that kind of missing the point. 512 bytes isn't much. Your comment is nearly a 5th of that budget.

by benj111

2/7/2026 at 11:46:48 PM

you bootstrap it into a library you can include optionally, duh

by pilord314

2/8/2026 at 8:01:54 AM

[flagged]

by userbinator

2/8/2026 at 11:58:06 AM

> but it seems there are others here who don't want to speak of the truth

Or you know, just didn't get hung up on the blatantly obvious thing not being explicitly disclaimed right in the title, only in the preamble?

by perching_aix

2/8/2026 at 8:43:14 PM

Not telling the whole truth, little-by-little, this is how honesty crumbles.

by userbinator

2/7/2026 at 10:02:13 PM

Nice. Very K&R-ish. Not a bad thing.

by kayo_20211030

2/8/2026 at 10:36:51 AM

[dead]

by MORPHOICES