;;; -*- lexical-binding: t -*-
;;
;; this file:
;;   https://dataswamp.org/~incal/emacs-init/variance.el
;;
;; For a file with tick-time integers (one at each line)
;; compute how much the ticks deviates from the desired
;; fixed-interrupt rate.

(require 'cl-lib)

(defun get-variance (mean)
  (save-excursion
    (goto-char (point-min))
    (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) )
            (cl-return) )))
      (/ sum offsets) )))

(defun tick-stats (desired-tick)
  (interactive "n desired tick: ")
  (save-excursion
    (goto-char (point-min))
    (let ((sum     0)
          (offsets 0)
          (max)
          (min) )
      (cl-loop
        (let((t0 (thing-at-point 'number)))
          (forward-line)
          (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))
                    (when (or (not max) (> offset max)) (setq max offset))
                    (when (or (not min) (> min offset)) (setq min offset))
                    (insert (format "%d\n" offset)) )
                (goto-char (point-min))
                (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) ))))))))

(provide 'variance)