ice-9/hcons.scm

   1 ;;; installed-scm-file
   2
   3 ;;;;    Copyright (C) 1995, 1996, 1998, 2001 Free Software Foundation, Inc.
   4 ;;;;
   5 ;;;; This program is free software; you can redistribute it and/or modify
   6 ;;;; it under the terms of the GNU General Public License as published by
   7 ;;;; the Free Software Foundation; either version 2, or (at your option)
   8 ;;;; any later version.
   9 ;;;;
  10 ;;;; This program is distributed in the hope that it will be useful,
  11 ;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 ;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13 ;;;; GNU General Public License for more details.
  14 ;;;;
  15 ;;;; You should have received a copy of the GNU General Public License
  16 ;;;; along with this software; see the file COPYING.  If not, write to
  17 ;;;; the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
  18 ;;;; Boston, MA 02111-1307 USA
  19 ;;;;
  20 ;;;; As a special exception, the Free Software Foundation gives permission
  21 ;;;; for additional uses of the text contained in its release of GUILE.
  22 ;;;;
  23 ;;;; The exception is that, if you link the GUILE library with other files
  24 ;;;; to produce an executable, this does not by itself cause the
  25 ;;;; resulting executable to be covered by the GNU General Public License.
  26 ;;;; Your use of that executable is in no way restricted on account of
  27 ;;;; linking the GUILE library code into it.
  28 ;;;;
  29 ;;;; This exception does not however invalidate any other reasons why
  30 ;;;; the executable file might be covered by the GNU General Public License.
  31 ;;;;
  32 ;;;; This exception applies only to the code released by the
  33 ;;;; Free Software Foundation under the name GUILE.  If you copy
  34 ;;;; code from other Free Software Foundation releases into a copy of
  35 ;;;; GUILE, as the General Public License permits, the exception does
  36 ;;;; not apply to the code that you add in this way.  To avoid misleading
  37 ;;;; anyone as to the status of such modified files, you must delete
  38 ;;;; this exception notice from them.
  39 ;;;;
  40 ;;;; If you write modifications of your own for GUILE, it is your choice
  41 ;;;; whether to permit this exception to apply to your modifications.
  42 ;;;; If you do not wish that, delete this exception notice.
  43 ;;;;
  44
  45 \f
  46 (define-module  (ice-9 hcons)
  47   :export (hashq-cons-hash hashq-cons-assoc hashq-cons-get-handle
  48            hashq-cons-create-handle! hashq-cons-ref hashq-cons-set! hashq-cons
  49            hashq-conser make-gc-buffer))
  50
  51 \f
  52 ;;; {Eq? hash-consing}
  53 ;;;
  54 ;;; A hash conser maintains a private universe of pairs s.t. if
  55 ;;; two cons calls pass eq? arguments, the pairs returned are eq?.
  56 ;;;
  57 ;;; A hash conser does not contribute life to the pairs it returns.
  58 ;;;
  59
  60 (define (hashq-cons-hash pair n)
  61   (modulo (logxor (hashq (car pair) 4194303)
  62                   (hashq (cdr pair) 4194303))
  63           n))
  64
  65 (define (hashq-cons-assoc key l)
  66   (and (not (null? l))
  67        (or (and (pair? l)               ; If not a pair, use its cdr?
  68                 (pair? (car l))
  69                 (pair? (caar l))
  70                 (eq? (car key) (caaar l))
  71                 (eq? (cdr key) (cdaar l))
  72                 (car l))
  73            (hashq-cons-assoc key (cdr l)))))
  74
  75 (define (hashq-cons-get-handle table key)
  76   (hashx-get-handle hashq-cons-hash hashq-cons-assoc table key #f))
  77
  78 (define (hashq-cons-create-handle! table key init)
  79   (hashx-create-handle! hashq-cons-hash hashq-cons-assoc table key init))
  80
  81 (define (hashq-cons-ref table key)
  82   (hashx-ref hashq-cons-hash hashq-cons-assoc table key #f))
  83
  84 (define (hashq-cons-set! table key val)
  85   (hashx-set! hashq-cons-hash hashq-cons-assoc table key val))
  86
  87 (define (hashq-cons table a d)
  88   (car (hashq-cons-create-handle! table (cons a d) #f)))
  89
  90 (define (hashq-conser hash-tab-or-size)
  91   (let ((table (if (vector? hash-tab-or-size)
  92                    hash-tab-or-size
  93                    (make-doubly-weak-hash-table hash-tab-or-size))))
  94     (lambda (a d) (hashq-cons table a d))))
  95
  96
  97 \f
  98
  99 (define (make-gc-buffer n)
 100   (let ((ring (make-list n #f)))
 101     (append! ring ring)
 102     (lambda (next)
 103       (set-car! ring next)
 104       (set! ring (cdr ring))
 105       next)))