mirror of
git://git.musl-libc.org/musl
synced 2025-01-13 10:21:30 +00:00
musl - an implementation of the standard library for Linux-based systems
20d01d83b5
due to the interface requirement of having the full state contained in a single object of type unsigned int, it is difficult to provide a reasonable-quality implementation; most good PRNGs are immediately ruled out because they need larger state. the old rand_r gave very poor output (very short period) in its lower bits; normally, it's desirable to throw away the low bits (as in rand()) when using a LCG, but this is not possible since the state is only 32 bits and we need 31 bits of output. glibc's rand_r uses the same LCG as musl's, but runs it for 3 iterations and only takes 10-11 bits from each iteration to construct the output value. this partially fixes the period issue, but introduces bias: not all outputs have the same frequency, and many do not appear at all. with such a low period, the bias is likely to be observable. I tried many approaches to "fix" rand_r, and the simplest I found which made it pass the "dieharder" tests was applying this transformation to the output. the "temper" function is taken from mersenne twister, where it seems to have been chosen for some rigorous properties; here, the only formal property I'm using is that it's one-to-one and thus avoids introducing bias. should further deficiencies in rand_r be reported, the obvious "best" solution is applying a 32-bit cryptographic block cipher in CTR mode. I identified several possible ciphers that could be used directly or adapted, but as they would be a lot slower and larger, I do not see a justification for using them unless the current rand_r proves deficient for some real-world use. |
||
|---|---|---|
| arch | ||
| crt | ||
| dist | ||
| include | ||
| lib | ||
| src | ||
| tools | ||
| .gitignore | ||
| configure | ||
| COPYRIGHT | ||
| INSTALL | ||
| Makefile | ||
| README | ||
| WHATSNEW | ||
musl libc - a new standard library to power a new generation of
Linux-based devices. musl is lightweight, fast, simple, free, and
strives to be correct in the sense of standards-conformance and
safety.
musl is an alternative to glibc, eglibc, uClibc, dietlibc, and klibc.
For reasons why one might prefer musl, please see the FAQ and libc
comparison chart on the project website,
http://www.musl-libc.org/
For installation instructions, see the INSTALL file.
Please refer to the COPYRIGHT file for details on the copyright and
license status of code included in musl (standard MIT license).
Greetings!
The 0.9.x release series for musl features interface coverage for all
interfaces defined in ISO C99 and POSIX 2008 base, along with a number
of non-standardized interfaces for compatibility with Linux, BSD, and
glibc functionality. As the release series progresses, we are
gradually adding support for incomplete functionality in existing
interfaces, additional functions that are deemed to be important due
to their use in real-world software, and support for new library and
language features in C11 such as thread-local storage, which is now
supported on all targets. In addition, support for additional target
cpu architectures is being added.
The number of packages build successfully against musl - either
out-of-the-box or with minor patches to address portability errors -
has exceeded 5000 and is steadily growing. In addition to application
compatibility testing, unit testing has been conducted using three
separate test frameworks and numerous additional standalone test cases
to verify the correctness of the implementation.
Included with this package is a gcc wrapper script (musl-gcc) which
allows you to build musl-linked programs using an existing gcc 3.x or
4.x toolchain on the host. There are also now at several mini
distributions (in the form of build scripts) which provide a
self-hosting musl-based toolchain and system root. These are much
better options than the wrapper script if you wish to use dynamic
linking or build packages with many library dependencies. See the musl
website for details.
The musl project is actively seeking contributors, mostly in the areas
of porting, testing, and application compatibility improvement. For
bug reports, support requests, or to get involved in development,
please visit #musl on Freenode IRC or subscribe to the musl mailing
list by sending a blank email to musl-subscribe AT lists DOT openwall
DOT com.
Thank you for using musl.
Cheers,
Rich Felker / dalias