If you're being technical, it's usually not a Taylor series, it's a minimax series. (The difference is that Taylor series minimize error at a given value, whereas minimax is trying to minimize maximum error in a range).
In most general math library implementations (e.g., the library in glibc, musl, etc.), the implementation of sin, as with most functions, is going to be a polynomial evaluation. See, e.g., https://github.com/kraj/musl/blob/kraj/master/src/math/__cos... for the implementation in musl, or https://github.com/bminor/glibc/blob/master/sysdeps/ieee754/... for glibc's implementation.
Of course, if you're not using a standard math library implementation, you're probably preferring speed over accuracy, and so you might use a lookup table and linear interpolation to get a very coarse approximation instead.
In Turns are Better than Radians (2022)bminor
glibc
C2015–2026
bminor / glibc · Archived
glibc
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| Period | Start (UTC) | End (exclusive, UTC) | Mentions | Submissions | Comments |
|---|---|---|---|---|---|
| 2015 | 2015-01-01 00:00:00 UTC | 2016-01-01 00:00:00 UTC | 1 | 0 | 1 |
| 2016 | 2016-01-01 00:00:00 UTC | 2017-01-01 00:00:00 UTC | 2 | 0 | 2 |
| 2017 | 2017-01-01 00:00:00 UTC | 2018-01-01 00:00:00 UTC | 0 | 0 | 0 |
| 2018 | 2018-01-01 00:00:00 UTC | 2019-01-01 00:00:00 UTC | 0 | 0 | 0 |
| 2019 | 2019-01-01 00:00:00 UTC | 2020-01-01 00:00:00 UTC | 3 | 0 | 3 |
| 2020 | 2020-01-01 00:00:00 UTC | 2021-01-01 00:00:00 UTC | 4 | 0 | 4 |
| 2021 | 2021-01-01 00:00:00 UTC | 2022-01-01 00:00:00 UTC | 10 | 0 | 10 |
| 2022 | 2022-01-01 00:00:00 UTC | 2023-01-01 00:00:00 UTC | 7 | 0 | 7 |
| 2023 | 2023-01-01 00:00:00 UTC | 2024-01-01 00:00:00 UTC | 8 | 0 | 8 |
| 2024 | 2024-01-01 00:00:00 UTC | 2025-01-01 00:00:00 UTC | 3 | 0 | 3 |
| 2025 | 2025-01-01 00:00:00 UTC | 2026-01-01 00:00:00 UTC | 6 | 0 | 6 |
| 2026 (partial) | 2026-01-01 00:00:00 UTC | 2027-01-01 00:00:00 UTC | 1 | 0 | 1 |
From the project README
An excerpt from the repository, fetched Nov 13, 2026.
Read the project’s introduction
This directory contains the sources of the GNU C Library.
See the file "version.h" for what release version you have.
The GNU C Library is the standard system C library for all GNU systems,
and is an important part of what makes up a GNU system. It provides the
system API for all programs written in C and C-compatible languages such
as C++ and Objective C; the runtime facilities of other programming
languages use the C library to access the underlying operating system.
In GNU/Linux systems, the C library works with the Linux kernel to
implement the operating system behavior seen by user applications.
In GNU/Hurd systems, it works with a microkernel and Hurd servers.
The GNU C Library implements much of the POSIX.1 functionality in the
GNU/Hurd system, using configurations i[4567]86-*-gnu and x86_64-gnu.
When working with Linux kernels, this version of the GNU C Library
requires Linux kernel version 3.2 or later.
Also note that the shared version of the libgcc_s library must be
installed for the pthread library to work correctly.
The GNU C Library supports these configurations for using Linux kernels:
aarch64*-*-linux-gnu
alpha*-*-linux-gnu
arc*-*-linux-gnu
arm-*-linux-gnueabi
csky-*-linux-gnuabiv2
hppa-*-linux-gnu
i[4567]86-*-linux-gnu
x86_64-*-linux-gnu Can build either x86_64 or x32
loongarch64-*-linux-gnu Hardware floating point, LE only.
m68k-*-linux-gnu
microblaze*-*-linux-gnu
mips-*-linux-gnu
mips64-*-linux-gnu
or1k-*-linux-gnu
powerpc-*-linux-gnu Hardware or software floating point, BE only.
powerpc64*-*-linux-gnu Big-endian and little-endian.
s390-*-linux-gnu
s390x-*-linux-gnu
riscv32-*-linux-gnu
riscv64-*-linux-gnu
sh[34]-*-linux-gnu
sparc*-*-linux-gnu
sparc64*-*-linux-gnu
If you are interested in doing a port, please contact the glibc
maintainers; see https://www.gnu.org/software/libc/ for more
information.
See the file INSTALL to find out how to configure, build, and install
the GNU C Library. You might also consider reading the WWW pages for
the C library at https://www.gnu.org/software/libc/.
The GNU C Library is (almost) completely documented by the Texinfo manual
found in the `manual/' subdirectory. The manual is still being updated
and contains some known errors and omissions; we regret that we do not
have the resources to work on the manual as much as we would like. For
corrections to the manual, please file a bug in the `manual' component,
following the bug-reporting instructions below. Please be sure to check
the manual in the current development sources to see if your problem has
already been corrected.
Please see https://www.gnu.org/software/libc/bugs.html for bug reporting
information. We are now using the Bugzilla system to track all bug reports.
This web page gives detailed information on how to report bugs properly.
The GNU C Library is free software. See the file COPYING.LIB for copying
conditions, and LICENSES for notices about a few contributions that require
these additional notices to be distributed. License copyright years may be
listed using range notation, e.g., 1996-2015, indicating that every year in
the range, inclusive, is a copyrightable year that would otherwise be listed
individually.
Read the full README on GitHubWhat Hacker News says
45 sourcesmemcpy (and the other string routines) are some of the library functions that most benefit from heavy optimisation and tuning for specific CPUs -- they get hit a lot, and careful adjustment of the code can get major performance wins by ensuring that the full memory bandwidth of the CPU is being used (which may involve using specific load instructions, deciding whether using the simd registers is better or not, and so on). So everybody who cares about performance optimises these routines pretty carefully, regardless of toolchain/OS. For instance the glibc versions are here:
https://github.com/bminor/glibc/tree/master/sysdeps/aarch64/...
and there are five versions specialised for either specific CPU models or for available architecture features.
In Ask HN: Why hasn't x86 caught up with Apple M series?That's fair, sorry for my casual language in a technically nuanced discussion. I hadn't looked at this in quite a while, but it was good to review. Thanks for the prompting.
https://github.com/bminor/glibc/blob/glibc-2.41/sysdeps/unix...
https://github.com/bminor/glibc/blob/glibc-2.41/sysdeps/unix...
In Path Isn't Real on LinuxYour process can be started in a paused state by a debugger, have new libraries and threads injected into it, and then resumed before a single instruction of your own binary has been executed... and debuggers are far from the only thing that will inject code into your processes. If you're willing to handwave that, pre-main constructors, etc. away, you can write something like this easily enough:
struct BeforeEnvFreeze(());
struct AfterEnvFreeze(());
impl BeforeEnvFreeze {
pub fn new() -> Self { /* singleton check using a static AtomicBool or something */ Self(()) }
pub fn freeze(self) -> AfterEnvFreeze { AfterEnvFreeze(()) }
pub fn set_env(&self, ...) { ... }
}
impl AfterEnvFreeze {
pub fn spawn_thread(&self, ...) { ... }
}
fn main() {
let a = BeforeEnvFreeze::new();
Read the rest
a.set_env(...);
a.set_env(...);
//b.spawn_thread(...); // not available
let b = a.freeze(); // consumes `a`
b.spawn_thread(...);
//a.set_env(...); // not available
}
Exercises left to the reader:
• Banning access to the relevant bits of Rust's stdlib, libc, etc. as a means of escaping this "safe" abstraction
• Conning your lead developer into accepting your handwave
• Setting up the appropriate VCS alerts so you have a chance to NAK "helpful" "utility" pull requests that undermine your "protections"
And of course, this all remains a hackaround for POSIX design flaws - your engineering time might be better spent ensuring or enforcing your libc is "fixed" via intentional memory leaks per e.g. https://github.com/bminor/glibc/commit/7a61e7f557a97ab597d6f... , which may ≈fix more than your Rust programs.
I'll take existence proofs [1] over personal insults but YMMV. You also may want to be careful assuming the expertise of people on this forum. Some people here are quite technical.
[1] https://github.com/bminor/glibc/commit/7a61e7f557a97ab597d6f...
In C stdlib isn't threadsafe and even safe Rust didn't save usIn the Rust std, `set_var` and `remove_var` will correctly require using an `unsafe {}` block in the next edition (2024). The documentation does now mention the safety issue but obviously it was a mistake to make these functions safe originally (albeit a mistake even higher level languages have made).
https://doc.rust-lang.org/stable/std/env/fn.set_var.html
There is a patch for glibc which makes `getenv` safe in more cases where the environment is modified but C still allows direct access to the environ so it can't be completely safe in the face of modification https://github.com/bminor/glibc/commit/7a61e7f557a97ab597d6f...
In C stdlib isn't threadsafe and even safe Rust didn't save usDepending on how you count, the ratio might not be that small. A lot of hot code are written in hand-coded inline assembly, so in terms of CPU cycles run it's probably non-negligible.
i.e. take a look at the glibc implementation of 'strcmp` [0]
[0] https://github.com/bminor/glibc/blob/master/sysdeps/x86_64/m...
In Don't Clobber the Frame PointerThe last argument would be on the stack instead of in a register which is where the kernel expects to find the arguments. But a proper syscall implementation would handle this just fine (e.g. <https://github.com/bminor/glibc/blob/ba60be873554ecd141b55ea...>), so I don't think there's anything sus about it.
In Linux Syscall SupportThat's not my reading.
> If the urandom source has not yet been initialized, then getrandom() will block, unless GRND_NONBLOCK is specified in flags.
And glibc's implementation doesn't specify any flags. https://github.com/bminor/glibc/blob/e67f8e6dbd5ec98578a775b...
Where as GRND_RANDOM is about switching to the random source instead of the urandom source.
> GRND_RANDOM
> If this bit is set, then random bytes are drawn from the random source (i.e., the same source as the /dev/random device) instead of the urandom source....
The combo seems to imply both sources can block, urandom is just less likely to.
https://man7.org/linux/man-pages/man2/getrandom.2.html
In Getentropy() vs. RAND_bytes()Most of the standard C library implementations, including FreeBSD's libc [0] and glibc [1] have sscanf implemented like that, by calling fscanf on a dummy FILE object (with its size populated by strlen() at every call, no caching).
Of course, there are implementations whose authors thought about that and decided to do the reasonable thing instead, e.g. musl [2] and Plauger's old stdlib [3].
[0] https://github.com/lattera/freebsd/blob/master/lib/libc/stdi...
[1] https://github.com/bminor/glibc/blob/dff8da6b3e89b986bb7f6b1... , https://github.com/bminor/glibc/blob/dff8da6b3e89b986bb7f6b1... , https://github.com/bminor/glibc/blob/dff8da6b3e89b986bb7f6b1... — two additional files and five times as much code compared to FreeBSD's implementation for pretty much the same functionality, wow.
[2] https://git.musl-libc.org/cgit/musl/tree/src/stdio/
Read the rest
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 whi
Read the rest
ch 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.
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...
In Setenv Is Not Thread Safe and C Doesn't Want to Fix ItDoes rust also add an pthread_atfork handler? Otherwise, it seems likely still unsafe for rust to claim to support calling fork (for execv) or posix_spawn, as most libc call realloc on the `environ` contents, but do not appear to take any care to ensure that (v)fork/posix_spawn doesn't happen concurrently with that. Worse yet, the `posix_spawnp` API takes an `envp` parameter and expects you to pass it the global pointer `environ`, which is completely unsynchronized across that fork call. It is not obvious to me that this is a security gap, but certainly it seems to me that this would violate rust's safety claim, if it is not taking added precautions there.
The Apple Libc appears to just unconditionally drops the environ lock in the child (https://github.com/apple-oss-distributions/Libc/blob/c5a3293...), while glibc doesn't appear to even
Read the rest
bother with that (https://github.com/bminor/glibc/blob/6ae7b5f43d4b13f24606d71...)
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 (well, in the kernel case you'll run into other limitations... but no memory corruption).
[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...
In CTF Writeup: Abusing select() to factor RSAAs one safety measure, compiling with -DFORTIFY_SOURCE > 0 will enable checks on the FD_SET etc macros:
https://github.com/bminor/glibc/commit/a0f33f996f7986dbf3763...
The kernel side interface probably won't change because apparently legitimate apps have been allocating fd_sets on the heap to monitor fds > 1024 and they don't want to break those:
https://sourceware.org/bugzilla/show_bug.cgi?id=10352#c7
The underlying problem was also discussed in an article by Lennart Poettering (of systemd fame) and posted to HN back in 2021:
https://news.ycombinator.com/item?id=27215690
https://0pointer.net/blog/file-descriptor-limits.html
In CTF Writeup: Abusing select() to factor RSAShowing the 15 most recent of 45 sources. Enable JavaScript to search and browse every indexed mention.