libc/src/stdlib/rand.cpp

   1 //===-- Implementation of rand --------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "src/stdlib/rand.h"
  10 #include "src/__support/common.h"
  11 #include "src/stdlib/rand_util.h"
  12
  13 namespace LIBC_NAMESPACE {
  14
  15 // An implementation of the xorshift64star pseudo random number generator. This
  16 // is a good general purpose generator for most non-cryptographics applications.
  17 LLVM_LIBC_FUNCTION(int, rand, (void)) {
  18   unsigned long x = rand_next;
  19   x ^= x >> 12;
  20   x ^= x << 25;
  21   x ^= x >> 27;
  22   rand_next = x;
  23   return static_cast<int>((x * 0x2545F4914F6CDD1Dul) >> 32) & RAND_MAX;
  24 }
  25
  26 } // namespace LIBC_NAMESPACE