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Weekend projects: getting silly with C

lcamtuf.substack.com

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Re: Weekend projects: getting silly with C

#5

Post by viraptor »

smusamashah wrote: post #3

Found these silly tricks by the author of this blog on twitter first. Switch statement can do loops too https://twitter.com/lcamtuf/status/1807129116980007037

Also on the actually social network https://infosec.exchange/@lcamtuf/112701486085621844

Re: Weekend projects: getting silly with C

#7

Post by nxobject »

If only there was a way of using setjmp/longjmp-style contexts instead of goto, un/winding the stack as required. So we could travel around in time... unfortunately you can't work with a setjmp buffer before it's actually created, unlike gotos.

Re: Weekend projects: getting silly with C

#8

Post by JohnMakin »

My undergrad was entirely in the C language and I’m very glad for it. Sometimes more modern languages can throw me for a loop, no pun intended, but the beauty (and horror) of C is that you are pretty close to the metal, it’s not very abstracted at all, and it allows you a lot of freedom (which is why it’s so foot gunny).

I will never love anything as much as I love C, but C development jobs lie in really weird fields I’m not interested in, and I’m fairly certain I am not talented enough. I have seen C wizardry up close that I know I simply cannot do. However, one of the more useful exercises I ever did was implement basic things like a file system, command line utilities like ls/mkdir etc. Sometimes they are surprisingly complex, sometimes no.

After you program in C for a while certain conventions meant to be extra careful kind of bubble up in languages in a way that seems weird to other people. for example I knew a guy that’d auto reject C PR’s if they didn’t use the syntax if (1==x) rather than if (x==1). The former will not compile if you accidentally use variable assignment instead of equality operator (which everyone has done at some point).

This tendency bites me a lot in some programming cultures, people (ime) tend to find this style of programming as overly defensive.

Re: Weekend projects: getting silly with C

#9

Post by tialaramex »

mgaunard wrote: post #2

aren't the switch shenanigans important to the duff's device?

Duff is relying on the fact you're allowed to intermingle the switch block and the loop in K&R C's syntax, the (common at the time but now generally frowned on or even prohibited in new languages) choice to drop-through cases if you don't explicitly break, and the related fact that C lets your loop jump back inside the switch.

Duff is trying to optimise MMIO, you wouldn't do anything close to this today even in C, not least because your MMIO is no longer similarly fast to your CPU instruction pace and for non-trivial amounts of data you have DMA (which Duff's hardware did not). In a modern language you also wouldn't treat "MMIO" as just pointer indirection, to make this stay working in C they have kept adding hacks to the type system rather than say OK, apparently this is an intrinsic, we should bake it into the freestanding mode of the stdlib.

Edited to add:

For my money the successor to Tom Duff's "Device" is WUFFS' "iterate loops" mechanism where you may specify how to partially unroll N steps of the loop, promising that this has equivalent results to running the main loop body N times but potentially faster. This makes it really easy for vectorisation to see what you're trying to do, while still handling those annoying corner cases where M % N != 0 correctly because that's the job of the tool, not the human.

Re: Weekend projects: getting silly with C

#10

Post by smackeyacky »

JohnMakin wrote: post #8

My undergrad was entirely in the C language and I’m very glad for it. Sometimes more modern languages can throw me for a loop, no pun intended, but the beauty (and horror) of C is that you are pretty close to the metal, it’s not very abstracted at all, and it allows you a lot of freedom (which is why it’s so foot gunny). I will never love anything as much as I love C, but C development jobs lie in really weird fields…

In an embedded environment, overly defensive is an asset
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