From: Stephen Adams <edu/mit/csail/zurich/adams>
Date: Sun, 30 Apr 1995 15:09:15 +0000 (+0000)
Subject: Changed COMPUTE-KEY-HASH to compute hash value optimistically and only
X-Git-Tag: 20090517-FFI~6365
X-Git-Url: https://birchwood-abbey.net/git?a=commitdiff_plain;h=3830d715002318763e687808a9f69798f1fe1b9c;p=mit-scheme.git

Changed COMPUTE-KEY-HASH to compute hash value optimistically and only
go into the SET-INTERRUPT-ENABLES! guarded loop if, as a post-check,
the table needs rehashing.

On a test case (the new compiler on list.scm) this reduces the
profiled time in SET-INTERRUPT-ENABLES! from 9.9% to 3.4%
---

diff --git a/v7/src/runtime/hashtb.scm b/v7/src/runtime/hashtb.scm
index e9387f38e..c11e9cb13 100644
--- a/v7/src/runtime/hashtb.scm
+++ b/v7/src/runtime/hashtb.scm
@@ -1,8 +1,8 @@
 #| -*-Scheme-*-
 
-$Id: hashtb.scm,v 1.20 1994/10/28 05:58:22 jawilson Exp $
+$Id: hashtb.scm,v 1.21 1995/04/30 15:09:15 adams Exp $
 
-Copyright (c) 1990-94 Massachusetts Institute of Technology
+Copyright (c) 1990-1995 Massachusetts Institute of Technology
 
 This material was developed by the Scheme project at the Massachusetts
 Institute of Technology, Department of Electrical Engineering and
@@ -688,20 +688,24 @@ MIT in each case. |#
 (define (compute-key-hash table key)
   (let ((key-hash (table-key-hash table)))
     (if (table-rehash-after-gc? table)
-	(let ((interrupt-mask (set-interrupt-enables! interrupt-mask/none)))
-	  (let loop ()
-	    (if (table-needs-rehash? table)
-		(begin
+	(let ((hash (key-hash key (vector-length (table-buckets table)))))
+	  (if (not (table-needs-rehash? table))
+	      hash
+	      (let ((interrupt-mask
+		     (set-interrupt-enables! interrupt-mask/none)))
+		(let loop ()
 		  (rehash-table! table)
 		  (if (< (table-count table) (table-shrink-size table))
 		      (begin
 			(set-interrupt-enables! interrupt-mask/gc-ok)
 			(shrink-table! table)
 			(set-interrupt-enables! interrupt-mask/none)
-			(loop))))))
-	  (let ((hash (key-hash key (vector-length (table-buckets table)))))
-	    (set-interrupt-enables! interrupt-mask)
-	    hash))
+			(if (table-needs-rehash? table)
+			    (loop)))))
+		(let ((hash
+		       (key-hash key (vector-length (table-buckets table)))))
+		  (set-interrupt-enables! interrupt-mask)
+		  hash))))
 	(key-hash key (vector-length (table-buckets table))))))
 
 (define-integrable (eq-hash-mod key modulus)