Info Catalog cl: Numerical Functions cl: Numbers cl: Implementation Parameters

cl: Random Numbers

 
 8.3 Random Numbers
 ==================
 
 This package also provides an implementation of the Common Lisp random
 number generator.  It uses its own additive-congruential algorithm,
 which is much more likely to give statistically clean random numbers
 than the simple generators supplied by many operating systems.
 
  -- Function: cl-random number &optional state
      This function returns a random nonnegative number less than NUMBER,
      and of the same type (either integer or floating-point).  The STATE
      argument should be a ‘random-state’ object that holds the state of
      the random number generator.  The function modifies this state
      object as a side effect.  If STATE is omitted, it defaults to the
      internal variable ‘cl--random-state’, which contains a
      pre-initialized default ‘random-state’ object.  (Since any number
      of programs in the Emacs process may be accessing
      ‘cl--random-state’ in interleaved fashion, the sequence generated
      from this will be irreproducible for all intents and purposes.)
 
  -- Function: cl-make-random-state &optional state
      This function creates or copies a ‘random-state’ object.  If STATE
      is omitted or ‘nil’, it returns a new copy of ‘cl--random-state’.
      This is a copy in the sense that future sequences of calls to
      ‘(cl-random N)’ and ‘(cl-random N S)’ (where S is the new
      random-state object) will return identical sequences of random
      numbers.
 
      If STATE is a ‘random-state’ object, this function returns a copy
      of that object.  If STATE is ‘t’, this function returns a new
      ‘random-state’ object seeded from the date and time.  As an
      extension to Common Lisp, STATE may also be an integer in which
      case the new object is seeded from that integer; each different
      integer seed will result in a completely different sequence of
      random numbers.
 
      It is valid to print a ‘random-state’ object to a buffer or file
      and later read it back with ‘read’.  If a program wishes to use a
      sequence of pseudo-random numbers which can be reproduced later for
      debugging, it can call ‘(cl-make-random-state t)’ to get a new
      sequence, then print this sequence to a file.  When the program is
      later rerun, it can read the original run’s random-state from the
      file.
 
  -- Function: cl-random-state-p object
      This predicate returns ‘t’ if OBJECT is a ‘random-state’ object, or
      ‘nil’ otherwise.
 

Info Catalog cl: Numerical Functions cl: Numbers cl: Implementation Parameters