4BSD libc random number generator

Linear congruential generator LCG with modulus m = 2^31, multiplier a = 1103515245 and increment c = 12345. Outputs 31 bits of randomness with more randomness in higher bits. Generator have full 2^31 period.

Features

1. Classic BSD / VAX / ANSI-C C library random number generator.
2. 15-bit K&R version included
3. Zero dependencies.
4. Safe Rust.
5. Non viral BSD-3 License.
6. libc style API.

References

This generator is listed in OESIS database as A096553.

15-bit version

1. https://oeis.org/A061364 - seed 1
2. https://oeis.org/A096554 - seed 0

Licensing

This package uses Revised BSD license.

Originally 4.4BSD-Lite2 got released under BSD-4 but it got relicensed as BSD-3. Advertising cause got removed. More info at: https://www.dragonflybsd.org/docs/developer/DragonFly_BSD_License/

Credits

This product includes software developed by the University of California, Berkeley and its contributors.

Upstream code

Code comes and is tested against 4.4BSD stdlib

1. https://github.com/sergev/4.4BSD-Lite2/tree/master/usr/src/lib/libc/stdlib
2. https://github.com/freebsd/freebsd-src/blob/releng/4.11/lib/libc/stdlib/rand.c
3. https://cvsweb.openbsd.org/src/lib/libc/stdlib/
4. https://github.com/NetBSD/src/blob/trunk/lib/libc/stdlib/rand.c
5. https://gitweb.dragonflybsd.org/dragonfly.git/tree/5daa25b05ec172803258b0c1f1148cadfccdba9e:/lib/libc/stdlib

History

1. Included in 2.9BSD, 3BSD and 4BSD, 4.1cBSD libc.
2. Included in SysVR4.
3. Included in AT&T Bell Labs V7, V7M and V9.
4. Included in AT&T's Unix Support Group (USG) SysIII.
5. SunOS 4.1, OpenSolaris compat-4.1 library.
6. Included in Ultrix-3.1.
7. Included in 4.1-compat part of 4.2BSD libc.
   • Its not clear yet in which BSD version this random number generator first appeared.
   • 4.2BSD documentation talks about weakness of this generator. I believe they wanted to replace it with something else.
   • They removed it from main BSD libc and left it only in backward 4.1-compat library.
   • In 4.3BSD-Tahoe it is still in 4.1-compat.
   • In 2.11BSD (Last 16 bit BSD PDP-11 distribution) it is in 4.1-compat.
   • In 4.3BSD-Reno generator is part of main libc again.
8. FreeBSD 5 replaced this algorithm with minstd0.
9. DragonFlyBSD merged FreeBSD change.
10. It is still in current NetBSD-10 source tree.
11. It is still in OpenBSD source tree.
12. Included in glibc-2.26
13. Standard C library (VAX C)
14. It is backend of K&R stdlib 15-bit rand().