Reimplement PRIME-NUMBERS-STREAM to use less space.

diff --git a/v7/src/runtime/stream.scm b/v7/src/runtime/stream.scm
index 2a0c6d50d2d7c845b4bd32aca545558dd702e3e3..440339ddc3078abd0c84b055a95b24ac5e081c37 100644 (file)
--- a/v7/src/runtime/stream.scm
+++ b/v7/src/runtime/stream.scm
@@ -1,9 +1,9 @@
 #| -*-Scheme-*-
 
-$Id: stream.scm,v 14.18 2003/09/30 04:22:59 cph Exp $
+$Id: stream.scm,v 14.19 2004/06/12 02:15:48 cph Exp $
 
 Copyright 1986,1987,1988,1989,1992,1995 Massachusetts Institute of Technology
-Copyright 1998,2003 Massachusetts Institute of Technology
+Copyright 1998,2003,2004 Massachusetts Institute of Technology
 
 This file is part of MIT/GNU Scheme.
 
@@ -265,22 +265,29 @@ USA.
   (cons-stream
    2
    (letrec
-       ((primes
-        (cons-stream
-         (cons 3 9)
-         (let filter ((integer 5))
-           (let loop ((primes primes))
-             (let ((prime (car primes)))
-               (cond ((< integer (cdr prime))
-                      (cons-stream (cons integer (square integer))
-                                   (filter (+ integer 2))))
-                     ((= 0 (remainder integer (car prime)))
-                      (filter (+ integer 2)))
-                     (else
-                      (loop (force (cdr primes)))))))))))
-     (let loop ((primes primes))
-       (cons-stream (car (car primes))
-                   (loop (force (cdr primes))))))))
+       ((primes (cons-stream 3 (fixnum-filter 5)))
+       (fixnum-filter
+        (let ((limit (fix:- (largest-fixnum) 2)))
+          (lambda (n)
+            (if (fix:<= n limit)
+                (let loop ((ps primes))
+                  (cond ((fix:< n (fix:* (car ps) (car ps)))
+                         (cons-stream n (fixnum-filter (fix:+ n 2))))
+                        ((fix:= 0 (fix:remainder n (car ps)))
+                         (fixnum-filter (fix:+ n 2)))
+                        (else
+                         (loop (force (cdr ps))))))
+                (generic-filter n)))))
+       (generic-filter
+        (lambda (n)
+          (let loop ((ps primes))
+            (cond ((< n (square (car ps)))
+                   (cons-stream n (generic-filter (+ n 2))))
+                  ((= 0 (remainder n (car ps)))
+                   (generic-filter (+ n 2)))
+                  (else
+                   (loop (force (cdr ps)))))))))
+     primes)))
 
 (define (initialize-package!)
   (let ((reset-primes!