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;;; srfi-27.scm --- Sources of Random Bits
;; Copyright (C) 2010 Free Software Foundation, Inc.
;; This library is free software; you can redistribute it and/or
;; modify it under the terms of the GNU Lesser General Public
;; License as published by the Free Software Foundation; either
;; version 3 of the License, or (at your option) any later version.
;; This library is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
;; Lesser General Public License for more details.
;; You should have received a copy of the GNU Lesser General Public
;; License along with this library. If not, see
;; <http://www.gnu.org/licenses/>.
;;; Commentary:
;; This module is fully documented in the Guile Reference Manual.
;;; Code:
(define-module (srfi srfi-27)
#: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)
#:use-module (srfi srfi-9))
(cond-expand-provide (current-module) '(srfi-27))
(define-record-type :random-source
(%make-random-source state)
random-source?
(state random-source-state set-random-source-state!))
(define (make-random-source)
(%make-random-source (seed->random-state 0)))
(define (random-source-state-ref s)
(random-state->datum (random-source-state s)))
(define (random-source-state-set! s state)
(set-random-source-state! s (datum->random-state state)))
(define (random-source-randomize! s)
(let ((time (gettimeofday)))
(set-random-source-state! s (seed->random-state
(+ (* (car time) 1e6) (cdr time))))))
(define (random-source-pseudo-randomize! s i j)
(set-random-source-state! s (seed->random-state (i+j->seed i j))))
(define (i+j->seed i j)
(logior (ash (spread i 2) 1)
(spread j 2)))
(define (spread n amount)
(let loop ((result 0) (n n) (shift 0))
(if (zero? n)
result
(loop (logior result
(ash (logand n 1) shift))
(ash n -1)
(+ shift amount)))))
(define (random-source-make-integers s)
(lambda (n)
(random n (random-source-state s))))
(define random-source-make-reals
(case-lambda
((s)
(lambda ()
(let loop ()
(let ((x (random:uniform (random-source-state s))))
(if (zero? x)
(loop)
x)))))
((s unit)
(or (and (real? unit) (< 0 unit 1))
(error "unit must be real between 0 and 1" unit))
(random-source-make-reals s))))
(define default-random-source (make-random-source))
(define random-integer (random-source-make-integers default-random-source))
(define random-real (random-source-make-reals default-random-source))
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