From 91a86cdb31f8f68f6cebd42ac6dae202adc3f8fe Mon Sep 17 00:00:00 2001
From: "H. Peter Anvin" <hpa@zytor.com>
Date: Fri, 31 Aug 2007 07:23:31 +0000
Subject: [PATCH] tokhash: Speed up the rejection of unhashed values

Speed up the rejection of unhashed values (typically identifiers) by
filling unused hash slots with a large value (but not so large that
it is likely to overflow.)  This means those values will be rejected
already by the range check, not needing strcmp().
---
 perllib/phash.ph | 12 +++++++++---
 tokhash.pl       | 11 +++++++++--
 2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/perllib/phash.ph b/perllib/phash.ph
index 017155d7..e17874a1 100644
--- a/perllib/phash.ph
+++ b/perllib/phash.ph
@@ -156,10 +156,16 @@ sub gen_hash_n($$$) {
     # for the edge (which is our hash index.)  Since the graph is
     # acyclic, this is always doable.
     for ($i = 0; $i < $gsize; $i++) {
-	if (!$gr->has_vertex_attribute($i, "val")) {
-	    walk_graph($gr,$i,0); # First vertex in a cluster
+	if ($gr->degree($i)) {
+	    # This vertex has neighbors (is used)
+	    if (!$gr->has_vertex_attribute($i, "val")) {
+		walk_graph($gr,$i,0); # First vertex in a cluster
+	    }
+	    push(@g, $gr->get_vertex_attribute($i, "val"));
+	} else {
+	    # Unused vertex
+	    push(@g, undef);
 	}
-	push(@g, $gr->get_vertex_attribute($i, "val"));
     }
 
     # for ($i = 0; $i < $n; $i++) {
diff --git a/tokhash.pl b/tokhash.pl
index 4730a8ba..9afe61dd 100755
--- a/tokhash.pl
+++ b/tokhash.pl
@@ -148,17 +148,24 @@ print "\n";
 print "int nasm_token_hash(const char *token, struct tokenval *tv)\n";
 print "{\n";
 
+# Put a large value in unused slots.  This makes it extremely unlikely
+# that any combination that involves unused slot will pass the range test.
+# This speeds up rejection of unrecognized tokens, i.e. identifiers.
+$unused = 16383;
+
 print "\tstatic const int16_t hash1[$n] =\n";
 print "\t{\n";
 for ($i = 0; $i < $n; $i++) {
-    print "\t\t", ${$g}[${$f1}[$i]], ",\n";
+    my $h = ${$g}[${$f1}[$i]];
+    printf "\t\t%d,\n", defined($h) ? $h : $unused;
 }
 print "\t};\n\n";
 
 print "\tstatic const int16_t hash2[$n] =\n";
 print "\t{\n";
 for ($i = 0; $i < $n; $i++) {
-    print "\t\t", ${$g}[${$f2}[$i]], ",\n";
+    my $h = ${$g}[${$f2}[$i]];
+    printf "\t\t%d,\n", defined($h) ? $h : $unused;
 }
 print "\t};\n\n";