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Original commit message from CVS: 2005-06-23 Andy Wingo <wingo@pobox.com> * tests/network-clock.scm: * tests/network-clock-utils.scm: A network clock simulator. Something of an algorithmic testbed before doing something in C.
150 lines
4 KiB
Scheme
150 lines
4 KiB
Scheme
;; GStreamer
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;; Copyright (C) 2005 Andy Wingo <wingo at pobox.com>
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;; This program is free software; you can redistribute it and/or
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;; modify it under the terms of the GNU General Public License as
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;; published by the Free Software Foundation; either version 2 of
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;; the License, or (at your option) any later version.
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;;
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;; This program is distributed in the hope that it will be useful,
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;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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;; GNU General Public License for more details.
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;;
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;; You should have received a copy of the GNU General Public License
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;; along with this program; if not, contact:
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;;
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;; Free Software Foundation Voice: +1-617-542-5942
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;; 59 Temple Place - Suite 330 Fax: +1-617-542-2652
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;; Boston, MA 02111-1307, USA gnu@gnu.org
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;;; Commentary:
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;;
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;; Utilities for the network clock simulator.
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;;
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;;; Code:
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;; General utilities.
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(define (iround x)
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(if (inexact? x)
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(inexact->exact (round x))
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x))
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(define (filter proc l)
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(cond
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((null? l) '())
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((proc (car l)) (cons (car l) (filter proc (cdr l))))
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(else (filter proc (cdr l)))))
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(define (sum l)
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(apply + l))
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(define (avg . nums)
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(/ (sum nums) (length nums)))
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(define (sq x)
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(* x x))
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;; Linear least squares.
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;;
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;; See http://mathworld.wolfram.com/LeastSquaresFitting.html
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;; returns (values slope intercept r-squared)
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(define (least-squares x y)
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(let ((n (length x)))
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(let ((xbar (apply avg x))
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(ybar (apply avg y)))
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(let ((sxx (- (sum (map sq x)) (* n (sq xbar))))
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(syy (- (sum (map sq y)) (* n (sq ybar))))
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(sxy (- (sum (map * x y)) (* n xbar ybar))))
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(let ((slope (/ sxy sxx)))
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(values
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slope
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(- ybar (* slope xbar))
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(/ (sq sxy) (* sxx syy))))))))
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;; Streams: lists with lazy cdrs.
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(define-macro (stream-cons kar kdr)
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`(cons ,kar (delay ,kdr)))
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(define (stream-cdr stream)
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(force (cdr stream)))
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(define (stream-car stream)
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(car stream))
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(define (stream-null? stream)
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(null? stream))
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(define (stream-ref stream n)
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(if (zero? n)
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(stream-car stream)
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(stream-ref (stream-cdr stream) (1- n))))
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(define (stream->list stream n)
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(let lp ((in stream) (out '()) (n n))
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(if (zero? n)
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(reverse! out)
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(lp (stream-cdr in) (cons (stream-car in) out) (1- n)))))
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(define (stream-skip stream n)
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(if (zero? n)
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stream
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(stream-skip (stream-cdr stream) (1- n))))
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(define (stream-sample stream n)
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(stream-cons (stream-car stream)
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(stream-sample (stream-skip stream n) n)))
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(define (stream-map proc . streams)
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(stream-cons (apply proc (map stream-car streams))
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(apply stream-map proc (map stream-cdr streams))))
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(define (arithmetic-series start step)
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(stream-cons start (arithmetic-series (+ start step) step)))
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(define (scale-stream stream factor)
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(stream-map (lambda (t) (* t factor)) *absolute-time*))
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(define (stream-while pred proc . streams)
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(if (apply pred (map stream-car streams))
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(begin
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(apply proc (map stream-car streams))
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(apply stream-while pred proc (map stream-cdr streams)))))
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(define (stream-of val)
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(stream-cons val (stream-of val)))
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(define (periodic-stream val period)
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(let ((period (iround (max 1 (* *sample-frequency* period)))))
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(let lp ((n 0))
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(if (zero? n)
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(stream-cons val (lp period))
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(stream-cons #f (lp (1- n)))))))
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;; Queues with a maximum length.
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(define *q-length* 32)
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(define (make-q l)
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(cons l (last-pair l)))
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(define (q-head q)
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(car q))
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(define (q-tail q)
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(car q))
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(define (q-push q val)
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(let ((tail (cons val '())))
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(if (null? (q-tail q))
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(make-q tail)
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(let ((l (append! (q-head q) tail)))
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(if (> (length (q-head q)) *q-length*)
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(make-q (cdr (q-head q)))
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q)))))
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