;;; -*- lexical-binding: t -*-

;; for a buffer/file of tick-time integers
;; one at each line
;; this Elisp number cruncher
;; is used to process the tick times
;; in order to find out how much
;; the ticks deviated
;; from the desired, fixed-interrupt rate

;; for the particular trace
;; stats are presented
;; as well as every drift from the specified ideal
;; as an indicator of an inexact clock
;; or if this needs to be further analyzed

(require 'cl-macs)

(defun get-variance (mean)
  (save-excursion
    (goto-char 1)
    (let ((sum 0) (offsets 0))
      (cl-loop
       (let ((offset (thing-at-point 'number)))
         (if offset
             (progn
               (cl-incf offsets)
               (setq sum (+ sum (expt (- offset mean) 2)))
               (forward-line 1) )
           (cl-return) )))
      (/ sum offsets) )))

(defun tick-stats (desired-tick)
  (interactive "n desired tick: ")
  (save-excursion
    (goto-char 1)
    (let ((sum 0) (offsets 0) (max nil) (min nil) )
      (cl-loop
       (let((t0 (thing-at-point 'number)))
         (forward-line 1)
         (let((t1 (thing-at-point 'number)))
           (save-current-buffer
             (set-buffer (get-buffer-create "offsets.log"))
             (if t1
                 (let((offset (- t1 t0 desired-tick)))
                   (cl-incf offsets)
                   (setq sum (+ sum offset))
                   (if (or (not max) (> offset max)) (setq max offset))
                   (if (or (not min) (> min offset)) (setq min offset))
                   (insert (format "%d\n" offset)) )
               (progn
                 (goto-char 1)
                 (insert
                  (let*((mean      (/ sum offsets))
                        (variance  (get-variance mean)) )
                    (format
                     "readings: %d\nmean: %f\nvariance: %f\nstandard deviation: %f\nmin: %d\nmax: %d\n\n"
                     offsets mean variance (sqrt variance) min max)))
                 (write-file "stats.log")
                 (cl-return) )))))))))