1  /* Fallback for fast jitter just return 0.
       2     Copyright (C) 2019-2023 Free Software Foundation, Inc.
       3     This file is part of the GNU C Library.
       4  
       5     The GNU C Library is free software; you can redistribute it and/or
       6     modify it under the terms of the GNU Lesser General Public
       7     License as published by the Free Software Foundation; either
       8     version 2.1 of the License, or (at your option) any later version.
       9  
      10     The GNU C Library is distributed in the hope that it will be useful,
      11     but WITHOUT ANY WARRANTY; without even the implied warranty of
      12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      13     Lesser General Public License for more details.
      14  
      15     You should have received a copy of the GNU Lesser General Public
      16     License along with the GNU C Library; if not, see
      17     <https://www.gnu.org/licenses/>.  */
      18  
      19  #ifndef _FAST_JITTER_H
      20  # define _FAST_JITTER_H
      21  
      22  # include <stdint.h>
      23  # include <hp-timing.h>
      24  
      25  /* Baseline just return 0.  We could create jitter using a clock or
      26     'random_bits' but that may imply a syscall and the goal of
      27     'get_fast_jitter' is minimal overhead "randomness" when such
      28     randomness helps performance.  Adding high overhead the function
      29     defeats the purpose.  */
      30  static inline uint32_t
      31  get_fast_jitter (void)
      32  {
      33  # if HP_TIMING_INLINE
      34    hp_timing_t jitter;
      35    HP_TIMING_NOW (jitter);
      36    return (uint32_t) jitter;
      37  # else
      38    return 0;
      39  # endif
      40  }
      41  
      42  #endif