rapidyaml
glibc
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rapidyaml | glibc | |
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13 | 45 | |
517 | 1,203 | |
- | 4.6% | |
5.7 | 9.8 | |
6 days ago | 6 days ago | |
C++ | C | |
MIT License | GNU General Public License v3.0 or later |
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For example, an activity of 9.0 indicates that a project is amongst the top 10% of the most actively developed projects that we are tracking.
rapidyaml
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Faces.js, a JavaScript library for generating vector-based cartoon faces
Interesting, I hadn't come across extism before. How hard would it be to package https://github.com/biojppm/rapidyaml in this way? (And do you have a extism for dummies guide?)
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A convenient C string API, friendly alongside classic C strings.
The inability, or brittleness, to embed NUL bytes into the string, for once. Zeroed bytes can be valid as an internal bytes of a longer encoded character. And the inefficiency of tempting every caller to rederive the string length on every use, leading to such bugs as quadratic parsing behavior with sscanf. The extra register for an explicit length is a very minute price to pay compared to that.
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Funniest line of code you wrote while making a game?
Although you still have the other problem of sscanf, where read times can become quadratic.
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yaml-cpp VS rapidyaml - a user suggested alternative
2 projects | 5 Feb 2022
- Since this is about json parsing and the tdarr json db can take ungodly times to load, maybe it's relevant?
- Parsing can become accidentally quadratic because of sscanf
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"Expanded and Enhanced"
You are really simplifying that issue. A lot of it has to be how the implementation of sscanf works and it's super easy to abuse by complete accident when a lot of data needs to be read and parsed to correct values. See more here: https://github.com/biojppm/rapidyaml/issues/40
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Accidentally quadratic: When Python is faster than C++
Leading to eye-rolling problems like these: https://github.com/biojppm/rapidyaml/issues/40
glibc
- I cut GTA Online loading times by 70% (2021)
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Cray-1 performance vs. modern CPUs
I wonder if you’re using a different definition of ‘vectorized’ from the one I would use. For example glibc provides a vectorized strlen. Here is the sse version: https://github.com/bminor/glibc/blob/master/sysdeps/x86_64/m...
It’s pretty simple to imagine how to write an unoptimized version: read a vector from the start of the string, compare it to 0, convert that to a bitvector, test for equal to zero, then loop or clz and finish.
I would call this vectorized because it operates on 16 bytes (sse) at a time.
There are a few issues:
1. You’re still spending a lot of time in the scalar code checking loop conditions.
2. You’re doing unaligned reads which are slower on old processors
3. You may read across a cache line forcing you to pull a second line into cache even if the string ends before then.
4. You may read across a page boundary which could cause a segfault if the next page is not accessible
So the fixes are to do 64-byte (ie cache line) aligned accesses which also means page-aligned (so you won’t read from a page until you know the string doesn’t end in the previous page). That deals with alignment problems. You read four vector registers at a time but this doesn’t really cost much more if the string is shorter as it all comes from one cache line. Another trick in the linked code is that it first finds the cache line by reading the first 16 bytes then merging in the next 3 groups with unsigned-min, so it only requires one test against a zero vector instead of 4. Then it finds the zero in the cache line. You need to do a bit of work in the first iteration to become aligned. With AVX, you can use mask registers on reads to handle that first step instead.
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Setenv Is Not Thread Safe and C Doesn't Want to Fix It
That was also my thought. To my knowledge `/etc/localtime` is the creation of Arthur David Olson, the founder of the tz database (now maintained by IANA), but his code never read `/etc/localtime` multiple times unless `TZ` environment variable was changed. Tzcode made into glibc but Ulrich Drepper changed it to not cache `/etc/localtime` when `TZ` is unset [1]; I wasn't able to locate the exact rationale, given that the commit was very ancient (1996-12) and no mailing list archive is available for this time period.
[1] https://github.com/bminor/glibc/commit/68dbb3a69e78e24a778c6...
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CTF Writeup: Abusing select() to factor RSA
That's not really what the problem is. The actual code is fine.
The issue is that the definition of `fd_set` has a constant size [1]. If you allocate the memory yourself, the select() system call will work with as many file descriptors as you care to pass to it. You can see that both glibc [2] and the kernel [3] support arbitrarily large arrays.
[1] https://github.com/bminor/glibc/blob/master/misc/sys/select....
[2] https://github.com/bminor/glibc/blob/master/sysdeps/unix/sys...
[3] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin...
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How are threads created in Linux x86_64
The source code for that is here.
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Using Uninitialized Memory for Fun and Profit (2008)
Expanding macro gives three GCC function attributes [2]: `__attribute__ ((malloc))`, `__attribute__ ((alloc_size(1)))` and `__attribute__ ((warn_unused_result))`. They are required for GCC (and others recognizing them) to actually ensure that they behave as the standard dictates. Your own malloc-like functions won't be treated same unless you give similar attributes.
[1] https://github.com/bminor/glibc/blob/807690610916df8aef17cd1...
[2] https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attribute...
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“csinc”, the AArch64 instruction you didn’t know you wanted
IFunc relocations is what enables glibc to dynamically choose the best memcpy routine to use at runtime based on the CPU.
see https://github.com/bminor/glibc/blob/glibc-2.31/sysdeps/x86_...
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memmove() implementation in strictly conforming C -- possible?
memmove can be very well implemented in pure C, libc implementations usually have a "generic" (meaning, architecture independent) fallback. Here is musl generic implementation and its x86-64 assembly implementation. For glibc, implementation is a bit more complex, having multiple architectures implemented, but you could find a generic implementation with these two files: memmove.c and generic/memcopy.h.
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Fedora 38 LLVM vs. Team Fortress 2
Yeah, looks like the Q_strcat(pszContentPath, "/"); is invalid, as glibc has only allocated exactly enough to fit the path in the buffer returned by realpath().
Interestingly, the open group spec says that a null argument to realpath is "Implementation defined" [0]
And the linux (glibc) man pages say it allocates a buffer "Up to PATH_MAX" [1]
I guess "strlen(path)" is "Up to PATH_MAX", but the man page seems unclear - you could read that as implying the buffer is always allocated to PATH_MAX size, but that's not what seems to be happening, just effectively calling strdup() [2]. I have no idea how to feed back to the linux man pages, but might be worth clarifying there.
[0] https://pubs.opengroup.org/onlinepubs/009696799/functions/re...
[1] https://linux.die.net/man/3/realpath
[2] https://github.com/bminor/glibc/blob/0b9d2d4a76508fdcbd9f421...
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Method implementations
For the actual sources you will have to look at one of the mirrors of the C standard library, such as https://github.com/bminor/glibc/tree/master/sysdeps/ieee754/dbl-64
What are some alternatives?
wasm3 - 🚀 A fast WebAssembly interpreter and the most universal WASM runtime
musl - Unofficial mirror of etalabs musl repository. Updated daily.
json-c - https://github.com/json-c/json-c is the official code repository for json-c. See the wiki for release tarballs for download. API docs at http://json-c.github.io/json-c/
cosmopolitan - build-once run-anywhere c library
degasolv - Democratize dependency management.
dns - DNS library in Go
Vrmac - Vrmac Graphics, a cross-platform graphics library for .NET. Supports 3D, 2D, and accelerated video playback. Works on Windows 10 and Raspberry Pi4.
0.30000000000000004 - Floating Point Math Examples
JitFromScratch - Example project from my talks in the LLVM Social Berlin and C++ User Group
ctl - The C Template Library