;;;
;;; mt-random - Mersenne Twister interface
;;;
;;;   Copyright (c) 2000-2014  Shiro Kawai  <shiro@acm.org>
;;;
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;;;   modification, are permitted provided that the following conditions
;;;   are met:
;;;
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;;;      notice, this list of conditions and the following disclaimer.
;;;
;;;   2. Redistributions in binary form must reproduce the above copyright
;;;      notice, this list of conditions and the following disclaimer in the
;;;      documentation and/or other materials provided with the distribution.
;;;
;;;   3. Neither the name of the authors nor the names of its contributors
;;;      may be used to endorse or promote products derived from this
;;;      software without specific prior written permission.
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;;;

(define-module math.mt-random
  (use gauche.uvector)
  (export <mersenne-twister>
          mt-random-set-seed!
          mt-random-get-state
          mt-random-set-state!
          mt-random-real
          mt-random-real0
          mt-random-integer
          mt-random-fill-u32vector!
          mt-random-fill-f32vector!
          mt-random-fill-f64vector!)
  )
(select-module math.mt-random)

(dynamic-load "math--mt-random")

(define (%get-nword-random-int mt n)
  (let loop ([i 0] [r (%mt-random-uint32 mt)])
    (if (= i n)
      r
      (loop (+ i 1)
            (+ (ash r 32) (%mt-random-uint32 mt))))))

(define (mt-random-integer mt n)
  (when (not (positive? n)) (error "invalid range" n))
  (if (<= n #x100000000)
    (%mt-random-integer mt n)
    (let* ([siz (ash (integer-length n) -5)]
           [q   (quotient (ash 1 (* 32 (+ siz 1))) n)]
           [qn  (* q n)])
      (let loop ([r (%get-nword-random-int mt siz)])
        (if (< r qn)
          (quotient r q)
          (loop (%get-nword-random-int mt siz)))))))

