;;; -*- lexical-binding: t -*-
;;
;; this file:
;;   https://dataswamp.org/~incal/emacs-init/epwgen.el
;;
;; 48 bits, alphabet length n, password length l
;; 2^48     = n^l            <=>
;; 48*ln(2) = l*ln(n)        <=>
;; l        = 48*ln(2)/ln(n)

(defun epwgen-password-length (bits abc)
  (let ((abc-len (if (numberp abc)
                     abc
                   (when (listp abc)
                     (length abc) ))))
    (when abc-len
      (/ (* bits (log 2)) (log abc-len)) )))

;; (epwgen-password-length 48 60)       ;  8.1
;; (epwgen-password-length 48 '(a b c)) ; 30.3
;; (epwgen-password-length 10 '(a b))   ; 10.0

(defun urandom (bits)
  (interactive "nbits: ")
  (let*((bytes     (/ bits 8))
        (bytes-opt (format "--bytes=%s" bytes)) )
    (with-temp-buffer
      (set-buffer-multibyte nil)
      (call-process "head" "/dev/urandom" t nil bytes-opt)
      (string-to-list
       (buffer-substring-no-properties (point-min) (point-max)) ))))
;; (urandom 100)

(provide 'epwgen)