mfbt/tests/TestRandomNum.cpp

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
   5  * You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #include "mozilla/RandomNum.h"
   8 #include <vector>
   9
  10 /*
  11
  12  * We're going to check that random number generation is sane on a basic
  13  * level - That is, we want to check that the function returns success
  14  * and doesn't just keep returning the same number.
  15  *
  16  * Note that there are many more tests that could be done, but to really test
  17  * a PRNG we'd probably need to generate a large set of randoms and
  18  * perform statistical analysis on them. Maybe that's worth doing eventually?
  19  *
  20  * For now we should be fine just performing a dumb test of generating 5
  21  * numbers and making sure they're all unique. In theory, it is possible for
  22  * this test to report a false negative, but with 5 numbers the probability
  23  * is less than one-in-a-trillion.
  24  *
  25  */
  26
  27 #define NUM_RANDOMS_TO_GENERATE 5
  28
  29 using mozilla::Maybe;
  30 using mozilla::RandomUint64;
  31
  32 static uint64_t getRandomUint64OrDie() {
  33   Maybe<uint64_t> maybeRandomNum = RandomUint64();
  34
  35   MOZ_RELEASE_ASSERT(maybeRandomNum.isSome());
  36
  37   return maybeRandomNum.value();
  38 }
  39
  40 static void TestRandomUint64() {
  41   // The allocator uses RandomNum.h too, but its initialization path allocates
  42   // memory. While the allocator itself handles the situation, we can't, so
  43   // we make sure to use an allocation before getting a Random number ourselves.
  44   std::vector<uint64_t> randomsList;
  45   randomsList.reserve(NUM_RANDOMS_TO_GENERATE);
  46
  47   for (uint8_t i = 0; i < NUM_RANDOMS_TO_GENERATE; ++i) {
  48     uint64_t randomNum = getRandomUint64OrDie();
  49
  50     for (uint64_t num : randomsList) {
  51       MOZ_RELEASE_ASSERT(randomNum != num);
  52     }
  53
  54     randomsList.push_back(randomNum);
  55   }
  56 }
  57
  58 int main() {
  59   TestRandomUint64();
  60   return 0;
  61 }