Import guile-1.8 as multiple upstream tarball component

[lilypond.git] / guile18 / ice-9 / hcons.scm

diff --git a/guile18/ice-9/hcons.scm b/guile18/ice-9/hcons.scm
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+;;; installed-scm-file
+
+;;;;   Copyright (C) 1995, 1996, 1998, 2001, 2003, 2006 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 2.1 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, write to the Free Software
+;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+;;;; 
+
+\f
+(define-module  (ice-9 hcons)
+  :export (hashq-cons-hash hashq-cons-assoc hashq-cons-get-handle
+          hashq-cons-create-handle! hashq-cons-ref hashq-cons-set! hashq-cons
+          hashq-conser make-gc-buffer))
+
+\f
+;;; {Eq? hash-consing}
+;;;
+;;; A hash conser maintains a private universe of pairs s.t. if 
+;;; two cons calls pass eq? arguments, the pairs returned are eq?.
+;;;
+;;; A hash conser does not contribute life to the pairs it returns.
+;;;
+
+(define (hashq-cons-hash pair n)
+  (modulo (logxor (hashq (car pair) 4194303)
+                 (hashq (cdr pair) 4194303))
+         n))
+
+(define (hashq-cons-assoc key l)
+  (and (not (null? l))
+       (or (and (pair? l)              ; If not a pair, use its cdr?
+               (pair? (car l))
+               (pair? (caar l))
+               (eq? (car key) (caaar l))
+               (eq? (cdr key) (cdaar l))
+               (car l))
+          (hashq-cons-assoc key (cdr l)))))
+
+(define (hashq-cons-get-handle table key)
+  (hashx-get-handle hashq-cons-hash hashq-cons-assoc table key))
+
+(define (hashq-cons-create-handle! table key init)
+  (hashx-create-handle! hashq-cons-hash hashq-cons-assoc table key init))
+
+(define (hashq-cons-ref table key)
+  (hashx-ref hashq-cons-hash hashq-cons-assoc table key #f))
+
+(define (hashq-cons-set! table key val)
+  (hashx-set! hashq-cons-hash hashq-cons-assoc table key val))
+
+(define (hashq-cons table a d)
+  (car (hashq-cons-create-handle! table (cons a d) #f)))
+
+(define (hashq-conser hash-tab-or-size)
+  (let ((table (if (vector? hash-tab-or-size)
+                  hash-tab-or-size
+                  (make-doubly-weak-hash-table hash-tab-or-size))))
+    (lambda (a d) (hashq-cons table a d))))
+
+
+\f
+
+(define (make-gc-buffer n)
+  (let ((ring (make-list n #f)))
+    (append! ring ring)
+    (lambda (next)
+      (set-car! ring next)
+      (set! ring (cdr ring))
+      next)))