jpegqs

9 ms·

31.
by jpegqs 5y ago
So far I've got these results: Allwinner H616 (Cortex-A53) 64-bit mode linux-5.15.7.tar.xz : 25.12 --> 24.43 (+3%) linux-firmware-20211027.tar.xz : 22.80 --> 21.63 (+5%) Maybe on more complex ARM processors the
32.
by jpegqs 5y ago
Cool, but it doesn't generate SBB in real code, but instead gives me something like this: xorl %r11d, %r11d cmpl %r12d, %eax seta %r11b And if I do both of these, side by side: tmp = rc.code < rc_bound ? ~0 :
33.
by jpegqs 5y ago
I tried it and realized that predicated instructions are removed from aarch64, which I was not aware of (because I rarely work with ARM). That sucks. But I'll try to do it without them.
34.
by jpegqs 5y ago
Can be done, ARM has better support for predicated instructions. May be done without using inline assembly. But I guess ARM CPUs can also have a smaller branch penalty, which means less speedup from such a patch. You can try it by replacing
35.
by jpegqs 5y ago
It would be great to have builtin for CMOV. But I also want GCC to utilize the hack with the SBB instruction when I write something like: (unsigned)a < (unsigned)b ? ~0 : 0 Instead of three instructions what it generates.
36.
by jpegqs 5y ago
LZMA compression (used in 7-zip, XZ, LZMA2) is known as one of the best, but it has a noticeable drawback - it's slow. I tried to improve the decompression speed by removing excessive branching at decoding of every bit from the compres
37.
Show HN: 10-40% faster LZMA decoder using x86 CMOVcc(gist.github.com)
205 points by jpegqs 5y ago|68 comments
38.
by jpegqs 5y ago
I'm porting Linux packages that compile for GCC/Clang to an EDG frontend based compiler and I need to remove forced -Werror from build scripts because different compilers have different warnings (and even false warnings due to com
39.
by jpegqs 5y ago
I made a windows port on github, you can try exploit that. ".//machine:foo/bar/baz" - will it work if the dot is added at the beginning?
40.
by jpegqs 5y ago
And now it compiles on Windows, at least with Msys2. I'm updating the code on github.
41.
by jpegqs 5y ago
It won't be a problem in this code because "%" is not handled. But could be a vulnerability for more implemented HTTP servers, and a few days ago I got this idea too.
42.
by jpegqs 5y ago
Yes, that's a vulnerability, I have fixed it on github.
43.
by jpegqs 5y ago
Thanks for noticing this, I fixed it on github. However, it seems that browsers are simply ignoring CRs. So that "\n\n" is enough.
44.
by jpegqs 5y ago
Thanks, I forgot about that. It would be very helpful to have some extra space for fixes.
45.
by jpegqs 5y ago
Good point, I need add something like b[3]='.', an then use b+3 as a path, not b+5, to fix that vulnerability. Update: I fixed this on github.
46.
by jpegqs 5y ago
I can explain it: m = n ? /* if (n != 0) */ /* adds index.html if path ends with "/" (means the filename is omitted), otherwise copies zero */ strcpy(b+i-1,b[i-2]-'/'?&qu
47.
by jpegqs 5y ago
It's calculated that strcpy() should never cause a buffer overflow here.
48.
by jpegqs 5y ago
I tried to make it secure and protect from such things. If someone finds vulnerabilities, please let me know.
49.
by jpegqs 5y ago
I have provided protection against this.
50.
by jpegqs 5y ago
It's cool if you can read code like this without issue. I'm chasing Kolmogorov complexity, rather than obfuscation. I add things like this to fill gaps in a specific shape.
51.
by jpegqs 5y ago
This is what I am arguing about with another IOCCC winner. What can be called obfuscation, and where are its boundaries.
52.
Show HN: Micro HTTP server in 22 lines of C(twitter.com)
223 points by jpegqs 5y ago|100 comments
53.
by jpegqs 5y ago
Can be both, a string and a function: char main [/*x86*/] __attribute__ ((section(".text")) )="WTYH)9Zj8_j7H)9]R" "H)9^\350\0\0\0\0H)1^R" "H))Z8<2u\366j&
54.
Fitting a FORTH in 512 bytes(niedzejkob.p4.team)
190 points by jpegqs 5y ago|57 comments
55.
POKEGB: A gameboy emulator that only plays Pokemon Blue, in 62 lines of C++(twitter.com)
2 points by jpegqs 5y ago|0 comments
56.
by jpegqs 6y ago
Location: Novosibirsk, Russia Remote: Yes Willing to relocate: Probably not Technologies: C/Assembly, SIMD (SSE/AVX/NEON/HVX and others), OpenCL, OpenMP Résumé/CV: https://www.linkedin.com/in/il
57.
Show HN: Obfuscated C code (IOCCC style) that I wrote last year(github.com)
4 points by jpegqs 6y ago|0 comments
58.
IOCCC 2020 Source Code Released(ioccc.org)
5 points by jpegqs 6y ago|0 comments
59.
by jpegqs 6y ago
The better way to check for buffer overflow here is "((unsigned T)i < n)". But the "(i >= 0 && i < n)" way that I used in this example - I have seen many times. So hackers can scan open source software c
60.
by jpegqs 6y ago
Thank you, I didn't know about this compiler option. Checked that the code works as expected with this option.

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