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;;; srfi-27.scm - Sources of Random Bits
;;;
;;; Copyright (c) 2000-2010 Shiro Kawai <shiro@acm.org>
;;;
;;; Redistribution and use in source and binary forms, with or without
;;; modification, are permitted provided that the following conditions
;;; are met:
;;;
;;; 1. Redistributions of source code must retain the above copyright
;;; 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.
;;;
;;; THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
;;; "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
;;; LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
;;; A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
;;; OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
;;; SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
;;; TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
;;; PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
;;; LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
;;; NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
;;; SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
;;;
;; Implements SRFI-27 interface on top of math.mt-random module.
(define-module srfi-27
(use math.mt-random)
(use srfi-4)
(export random-integer random-real default-random-source
make-random-source random-source?
random-source-state-ref random-source-state-set!
random-source-randomize! random-source-pseudo-randomize!
random-source-make-integers random-source-make-reals
))
(select-module srfi-27)
;; Assumes random source is <mersenne-twister> random object for now.
;; It is possible that I extend the implementation so that users can
;; specify the class of random source in future.
(define-constant random-source <mersenne-twister>)
;; Operations on random source
(define (make-random-source) (make random-source))
(define (random-source? obj) (is-a? obj random-source))
(define default-random-source (make-random-source))
(define (random-source-state-ref source)
(mt-random-get-state source))
(define (random-source-state-set! source state)
(mt-random-set-state! source state))
;; Randomize
(define (random-source-randomize! source)
(unless (random-source? source)
(error "random source required, but got" source))
(mt-random-set-seed! source
(let1 s (* (inexact->exact (sys-time)) (sys-getpid))
(logior s (ash s -16)))))
(define (random-source-pseudo-randomize! source i j)
;; This procedure is effectively required to map integers (i,j) into
;; a seed value in a deterministic way. Talking advantage of the fact
;; that Mersenne Twister can take vector of numbers.
;; interleave-i and interleave-j creates a list of integers, each
;; is less than 2^32, consisted by interleaving each 32-bit chunk of i and j.
(define (interleave-i i j lis)
(if (zero? i)
(if (zero? j) lis (interleave-j 0 j (cons 0 lis)))
(receive (q r) (quotient&remainder i #x100000000)
(interleave-j q j (cons r lis)))))
(define (interleave-j i j lis)
(if (zero? j)
(if (zero? i) lis (interleave-i i 0 (cons 0 lis)))
(receive (q r) (quotient&remainder j #x100000000)
(interleave-i i q (cons r lis)))))
;; main body
(unless (random-source? source)
(error "random source required, but got" source))
(when (or (not (integer? i)) (not (integer? j))
(negative? i) (negative? j))
(errorf "indices must be non-negative integers: ~s, ~s" i j))
(mt-random-set-seed! source
(list->u32vector (interleave-i i j '(#xffffffff))))
)
;; Obtain generators from random source.
(define (random-source-make-integers source)
(unless (random-source? source)
(error "random source required, but got" source))
(lambda (n) (mt-random-integer source n)))
(define (random-source-make-reals source . maybe-unit)
(unless (random-source? source)
(error "random source required, but got" source))
(if (null? maybe-unit)
(lambda () (mt-random-real source))
(let1 unit (car maybe-unit)
(unless (< 0 unit 1)
(error "unit must be between 0.0 and 1.0 (exclusive), but got" unit))
(let* ((1/unit (/. unit))
(range (ceiling->exact 1/unit)))
(lambda ()
(/ (random-integer range) 1/unit))))))
;; Default random generators.
(define-values (random-integer random-real)
(let1 src default-random-source
(values (lambda (n) (mt-random-integer src n))
(lambda () (mt-random-real src)))))
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