thodg/libgit2/src/rand.h

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• Hash : 3c53796c
  Author :
  Date : 2022-02-07T19:38:32
  

  rand: introduce git_rand PRNG
  
  Introduce `git_rand`, a PRNG based on xoroshiro256**, a fast,
  all-purpose pseudo-random number generator: https://prng.di.unimi.it
  
  The PRNG will be seeded by the system's entropy store when possible,
  falling back to current time and system data (pid, uptime, etc).
  Inspiration for this was taken from libressl, but since our PRNG is
  not used for cryptographic purposes (and indeed currently only generates
  a unique temp file name that is written in a protected directory),
  this should be more than sufficient.
  
  Our implementation of xoroshiro256** was taken almost strictly from
  the original author's sources, but was tested against PractRand to
  ensure that there were no foolish mistranslations:
  
  ```
  RNG_test using PractRand version 0.94
  RNG = RNG_stdin64, seed = unknown
  test set = core, folding = standard (64 bit)
  
  rng=RNG_stdin64, seed=unknown
  length= 256 megabytes (2^28 bytes), time= 2.9 seconds
    no anomalies in 210 test result(s)
  
  rng=RNG_stdin64, seed=unknown
  length= 512 megabytes (2^29 bytes), time= 6.2 seconds
    no anomalies in 226 test result(s)
  
  rng=RNG_stdin64, seed=unknown
  length= 1 gigabyte (2^30 bytes), time= 12.7 seconds
    no anomalies in 243 test result(s)
  
  rng=RNG_stdin64, seed=unknown
  length= 2 gigabytes (2^31 bytes), time= 25.4 seconds
    no anomalies in 261 test result(s)
  
  rng=RNG_stdin64, seed=unknown
  length= 4 gigabytes (2^32 bytes), time= 50.6 seconds
    no anomalies in 277 test result(s)
  
  rng=RNG_stdin64, seed=unknown
  length= 8 gigabytes (2^33 bytes), time= 104 seconds
    no anomalies in 294 test result(s)
  ```
  

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• src/rand.h

• /*
   * Copyright (C) the libgit2 contributors. All rights reserved.
   *
   * This file is part of libgit2, distributed under the GNU GPL v2 with
   * a Linking Exception. For full terms see the included COPYING file.
   */
  #ifndef INCLUDE_rand_h__
  #define INCLUDE_rand_h__
  
  #include "common.h"
  
  /**
   * Initialize the random number generation subsystem.  This will
   * seed the random number generator with the system's entropy pool,
   * if available, and will fall back to the current time and
   * system information if not.
   */
  int git_rand_global_init(void);
  
  /**
   * Seed the pseudo-random number generator.  This is not needed to be
   * called; the PRNG is seeded by `git_rand_global_init`, but it may
   * be useful for testing.  When the same seed is specified, the same
   * sequence of random numbers from `git_rand_next` is emitted.
   *
   * @param seed the seed to use
   */
  void git_rand_seed(uint64_t seed);
  
  /**
   * Get the next pseudo-random number in the sequence.
   *
   * @return a 64-bit pseudo-random number
   */
  uint64_t git_rand_next(void);
  
  #endif
  

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