The function random is a bit slow, can it be optimized?

[xizang]

Hi,
Random numbers are frequently used in machine learning algorithms, but the random function of sbcl is a bit slow. Can it be optimized?

(time (dotimes (i 1000000)
        (random 1.0 (make-random-state t))))
Evaluation took:
  135.454 seconds of real time
  135.443309 seconds of total run time (19.848173 user, 115.595136 system)
  [ Real times consist of 0.095 seconds GC time, and 135.359 seconds non-GC time. ]
  [ Run times consist of 0.093 seconds GC time, and 135.351 seconds non-GC time. ]
  99.99% CPU
  393,361,050,731 processor cycles
  3,423,087,968 bytes consed

In src/code/target-random.lisp

#-win32
(defun os-random-seed ()
  (or
   ;; On unices, we try to read from /dev/urandom and pass the results
   ;; to our (simple-array (unsigned-byte 32) (*)) processor below.
   ;; More than 256 bits would provide a false sense of security.
   ;; If you need more bits than that, you probably also need
   ;; a better algorithm too.
   (ignore-errors
    (with-open-file (r "/dev/urandom" :element-type '(unsigned-byte 32)
                                      :direction :input :if-does-not-exist :error)
      (let ((a (make-array '(8) :element-type '(unsigned-byte 32))))
        (aver (= 8 (read-sequence a r)))
        a)))
   (fallback-random-seed)
   ))

(defun fallback-random-seed ()
  ;; When /dev/urandom is not available, we make do with time and pid
  ;; Thread ID and/or address of a CONS cell would be even better, but...
  ;; [ADDRESS-BASED-COUNTER-VAL in 'target-sxhash' could be used here]
  (/show0 "No /dev/urandom, using randomness from time and pid")
  (+ (get-internal-real-time)
     (ash (sb-unix:unix-getpid) 32)))

Can these two functions be improved like this?
#-win32
(defun os-random-seed ()
  (or
   ;; On unices, we try to read from /dev/urandom and pass the results
   ;; to our (simple-array (unsigned-byte 32) (*)) processor below.
   ;; More than 256 bits would provide a false sense of security.
   ;; If you need more bits than that, you probably also need
   ;; a better algorithm too.
   (fallback-random-seed) ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; change this
   (ignore-errors
    (with-open-file (r "/dev/urandom" :element-type '(unsigned-byte 32)
                                      :direction :input :if-does-not-exist :error)
      (let ((a (make-array '(8) :element-type '(unsigned-byte 32))))
        (aver (= 8 (read-sequence a r)))
        a)))
   ))

(defun fallback-random-seed ()
  ;; When /dev/urandom is not available, we make do with time and pid
  ;; Thread ID and/or address of a CONS cell would be even better, but...
  ;; [ADDRESS-BASED-COUNTER-VAL in 'target-sxhash' could be used here]
  (/show0 "No /dev/urandom, using randomness from time and pid")
  (multiple-value-bind (sec usec)
      (get-time-of-day)
    (+ sec (ash usec 8))))

Now,

 (time (dotimes (i 1000000)
        (random 1.0 (make-random-state t))))
Evaluation took:
  3.991 seconds of real time
  3.993465 seconds of total run time (3.980038 user, 0.013427 system)
  [ Real times consist of 0.070 seconds GC time, and 3.921 seconds non-GC time. ]
  [ Run times consist of 0.069 seconds GC time, and 3.925 seconds non-GC time. ]
  100.05% CPU
  11,592,835,590 processor cycles
  2,543,946,064 bytes consed

Best regards！

[Stas Boukarev (stassats)]

Don't do (make-random-state t) on each iteration.