text: /*
   *
   * Copyright 2016, Google Inc.
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions are
   * met:
   *
   *     * Redistributions of source code must retain the above copyright
   * notice, this list of conditions and the following disclaimer.
   *     * Redistributions in binary form must reproduce the above
   * copyright notice, this list of conditions and the following disclaimer
   * in the documentation and/or other materials provided with the
   * distribution.
   *     * Neither the name of Google Inc. nor the names of its
   * contributors may be used to endorse or promote products derived from
   * this software without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
   * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
   * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
   * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
   * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   *
   */
  
  #include "src/core/lib/support/backoff.h"
  
  #include <grpc/support/useful.h>
  
  void gpr_backoff_init(gpr_backoff *backoff, int64_t initial_connect_timeout,
                        double multiplier, double jitter,
                        int64_t min_timeout_millis, int64_t max_timeout_millis) {
    backoff->initial_connect_timeout = initial_connect_timeout;
    backoff->multiplier = multiplier;
    backoff->jitter = jitter;
    backoff->min_timeout_millis = min_timeout_millis;
    backoff->max_timeout_millis = max_timeout_millis;
    backoff->rng_state = (uint32_t)gpr_now(GPR_CLOCK_REALTIME).tv_nsec;
  }
  
  gpr_timespec gpr_backoff_begin(gpr_backoff *backoff, gpr_timespec now) {
    backoff->current_timeout_millis = backoff->initial_connect_timeout;
    const int64_t first_timeout =
        GPR_MAX(backoff->current_timeout_millis, backoff->min_timeout_millis);
    return gpr_time_add(now, gpr_time_from_millis(first_timeout, GPR_TIMESPAN));
  }
  
  /* Generate a random number between 0 and 1. */
  static double generate_uniform_random_number(uint32_t *rng_state) {
    *rng_state = (1103515245 * *rng_state + 12345) % ((uint32_t)1 << 31);
    return *rng_state / (double)((uint32_t)1 << 31);
  }
  
  gpr_timespec gpr_backoff_step(gpr_backoff *backoff, gpr_timespec now) {
    const double new_timeout_millis =
        backoff->multiplier * (double)backoff->current_timeout_millis;
    backoff->current_timeout_millis =
        GPR_MIN((int64_t)new_timeout_millis, backoff->max_timeout_millis);
  
    const double jitter_range_width = backoff->jitter * new_timeout_millis;
    const double jitter =
        (2 * generate_uniform_random_number(&backoff->rng_state) - 1) *
        jitter_range_width;
  
    backoff->current_timeout_millis =
        (int64_t)((double)(backoff->current_timeout_millis) + jitter);
  
    const gpr_timespec current_deadline = gpr_time_add(
        now, gpr_time_from_millis(backoff->current_timeout_millis, GPR_TIMESPAN));
  
    const gpr_timespec min_deadline = gpr_time_add(
        now, gpr_time_from_millis(backoff->min_timeout_millis, GPR_TIMESPAN));
  
    return gpr_time_max(current_deadline, min_deadline);
  }
  
  void gpr_backoff_reset(gpr_backoff *backoff) {
    backoff->current_timeout_millis = backoff->initial_connect_timeout;
  }
  