forked from OSchip/llvm-project
00582563be
Summary: This follows the addition of `GetRandom` with D34412. We remove our `/dev/urandom` code and use the new function. Additionally, change the PRNG for a slightly faster version. One of the issues with the old code is that we have 64 full bits of randomness per "next", using only 8 of those for the Salt and discarding the rest. So we add a cached u64 in the PRNG that can serve up to 8 u8 before having to call the "next" function again. During some integration work, I also realized that some very early processes (like `init`) do not benefit from `/dev/urandom` yet. So if there is no `getrandom` syscall as well, we have to fallback to some sort of initialization of the PRNG. Now a few words on why XoRoShiRo and not something else. I have played a while with various PRNGs on 32 & 64 bit platforms. Some results are below. LCG 32 & 64 are usually faster but produce respectively 15 & 31 bits of entropy, meaning that to get a full 64-bit, you would need to call them several times. The simple XorShift is fast, produces 32 bits but is mediocre with regard to PRNG test suites, PCG is slower overall, and XoRoShiRo is faster than XorShift128+ and produces full 64 bits. %%% root@tulip-chiphd:/data # ./randtest.arm [+] starting xs32... [?] xs32 duration: 22431833053ns [+] starting lcg32... [?] lcg32 duration: 14941402090ns [+] starting pcg32... [?] pcg32 duration: 44941973771ns [+] starting xs128p... [?] xs128p duration: 48889786981ns [+] starting lcg64... [?] lcg64 duration: 33831042391ns [+] starting xos128p... [?] xos128p duration: 44850878605ns root@tulip-chiphd:/data # ./randtest.aarch64 [+] starting xs32... [?] xs32 duration: 22425151678ns [+] starting lcg32... [?] lcg32 duration: 14954255257ns [+] starting pcg32... [?] pcg32 duration: 37346265726ns [+] starting xs128p... [?] xs128p duration: 22523807219ns [+] starting lcg64... [?] lcg64 duration: 26141304679ns [+] starting xos128p... [?] xos128p duration: 14937033215ns %%% Reviewers: alekseyshl Reviewed By: alekseyshl Subscribers: aemerson, kristof.beyls, llvm-commits Differential Revision: https://reviews.llvm.org/D35221 llvm-svn: 307798 |
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| cmake | ||
| docs | ||
| include | ||
| lib | ||
| test | ||
| unittests | ||
| www | ||
| .arcconfig | ||
| .gitignore | ||
| CMakeLists.txt | ||
| CODE_OWNERS.TXT | ||
| CREDITS.TXT | ||
| LICENSE.TXT | ||
| README.txt | ||
README.txt
Compiler-RT ================================ This directory and its subdirectories contain source code for the compiler support routines. Compiler-RT is open source software. You may freely distribute it under the terms of the license agreement found in LICENSE.txt. ================================