src/code/random.lisp

   1 ;;;; This software is part of the SBCL system. See the README file for
   2 ;;;; more information.
   3 ;;;;
   4 ;;;; This software is derived from the CMU CL system, which was
   5 ;;;; written at Carnegie Mellon University and released into the
   6 ;;;; public domain. The software is in the public domain and is
   7 ;;;; provided with absolutely no warranty. See the COPYING and CREDITS
   8 ;;;; files for more information.
   9
  10 (in-package "SB!KERNEL")
  11
  12 ;;; the size of the chunks returned by RANDOM-CHUNK
  13 (def!constant random-chunk-length 32)
  14
  15 ;;; the amount that we overlap chunks by when building a large integer
  16 ;;; to make up for the loss of randomness in the low bits
  17 (def!constant random-integer-overlap 3)
  18
  19 ;;; extra bits of randomness that we generate before taking the value MOD the
  20 ;;; limit, to avoid loss of randomness near the limit
  21 (def!constant random-integer-extra-bits 10)
  22
  23 ;;; the largest fixnum we can compute from one chunk of bits
  24 (def!constant random-fixnum-max
  25   (1- (ash 1 (- random-chunk-length random-integer-extra-bits))))
  26
  27 (sb!xc:defstruct (random-state (:constructor %make-random-state)
  28                                (:copier nil)) ; since shallow copy is wrong
  29   (state (init-random-state) :type (simple-array (unsigned-byte 32) (627))))