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;; This file is part of GNUnet.
;; Copyright (C) 2001-2013, 2018 GNUnet e.V.
;;
;; GNUnet is free software: you can redistribute it and/or modify it
;; under the terms of the GNU Affero General Public License as published
;; by the Free Software Foundation, either version 3 of the License,
;; or (at your option) any later version.
;;
;; GNUnet is distributed in the hope that it will be useful, but
;; WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
;; Affero General Public License for more details.
;;
;; You should have received a copy of the GNU Affero General Public License
;; along with this program. If not, see <http://www.gnu.org/licenses/>.
;;
;; SPDX-License-Identifier: AGPL3.0-or-later
;; C file: util/time.c
;; Author: Christian Grothoff
;; Partially adapted to Scheme by Maxime Devos
;; Synopsis: procedures for handling time and time arithmetic
(define-library (gnu gnunet util time)
(export time-unit:zero time-unit:microsecond time-unit:millisecond
time-unit:second time-unit:minute time-unit:hour
standard-back-off)
(import (only (rnrs base)
assert integer? exact <= define begin min * max
and exact? >= /))
(begin
(define time-unit:zero 0)
(define time-unit:microsecond 1)
(define time-unit:millisecond 1000)
(define time-unit:second (* 1000 1000))
(define time-unit:minute (* 60 time-unit:second))
(define time-unit:hour (* 60 time-unit:minute))
(define (exact-natural? x)
(and (integer? x) (exact? x) (>= x 0)))
;; Treshold after which exponential backoff should not increase
;; (15 minutes).
(define standard-exponential-backoff-treshold
(/ time-unit:hour 4))
(define (standard-back-off relative-time)
"Perform our standard exponential back-off calculation, starting at
1 millisecond and then going by a factor of 2 up unto a maximum of 15 minutes.
The current backoff time is @var{relative-time}. Initially it is zero."
(assert (exact-natural? relative-time))
(min standard-exponential-backoff-treshold
(* 2 (max time-unit:millisecond relative-time))))))
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