String 以最快的方式生成随机字符串

我目前正在使用：

(defvar my-charset
  (eval-when-compile
    (concat (number-sequence 48 57) (number-sequence 65 90) (number-sequence 97 122)))
  "Char set in terms of number list.")
(defvar my-charset-length
  (eval-when-compile
    (length (concat (number-sequence 48 57) (number-sequence 65 90) (number-sequence 97 122))))
  "Length of my-charset.")

(defun my-generate-string (&optional max-length min-length)
  "Generate a random string."
  (let (string)
    (dotimes (_i (+ (random (- (or max-length 10) (or min-length 5) -1)) (or min-length 5)))
      (push (aref my-charset (random my-charset-length)) string))
    (concat string)))

有什么方法可以加快速度吗

---

或者任何其他更快生成字符串的方法？

通过更有效地使用数据（和控制）结构，可以获得较小的性能增益

(defconst our-charset "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz")
(defconst our-charset-length (length our-charset))

(defun my-generate-string (&optional max-length min-length)
  "Generate a random string."
  (let (string)
    (dotimes (_i (+ (random (- (or max-length 10) (or min-length 5) -1)) (or min-length 5)))
      (push (aref our-charset (random our-charset-length)) string))
    (concat string)))

(defun our-generate-string (&optional max-length min-length)
  (let* ((max-length (or max-length 10))
         (min-length (or min-length 5))
         (length (+ min-length (random (- max-length min-length -1))))
         (string (make-string length ?0)))
    (dotimes (i length string)
      (aset string i
            (aref our-charset (random our-charset-length))))))

(defmacro measure-time (&rest body)
  `(let ((time (current-time)))
     ,@body
     (float-time (time-since time))))

(/
 (apply #'+
        (mapcar
         (lambda (ignore) (measure-time (my-generate-string 1000 999)))
         (number-sequence 0 999)))
 1000)
;; 0.0018966329990000002

(/
 (apply #'+
        (mapcar
         (lambda (ignore) (measure-time (our-generate-string 1000 999)))
         (number-sequence 0 999)))
 1000)
;; 0.0009833975549999997

根据硬件和随机性，您的结果可能会有所不同，但是

我们的生成字符串

应该更快

你可能还想稍微调整一下你的通话习惯

(defun our-randomized-string (charset length)
  (let ((charset-length (length charset))
        (string (make-string length ?0)))
    (dotimes (i length string)
      (aset string i
            (aref charset (random charset-length))))))

(/
 (apply #'+
        (mapcar
         (lambda (ignore) (measure-time (our-randomized-string our-charset 1000)))
         (number-sequence 0 999)))
 1000)
 ;; 0.0009300809320000015

请注意，

我们的随机化字符串

不一定比

我们的生成字符串

快，但是能够在函数外部修复参数而不是在函数内部确定参数可能最终会带来好处。在这个版本中，字符集的交换也比在另一个版本中更容易。

您需要多大的“随机性”？