I see no reason why this should be signed.
And cast to int may clobber big values!

diff -ur gawk-3.1.1.orig/awkgram.y gawk-3.1.1/awkgram.y
--- gawk-3.1.1.orig/awkgram.y	Tue Apr 16 13:40:13 2002
+++ gawk-3.1.1/awkgram.y	Wed May 22 10:54:37 2002
@@ -1124,7 +1124,7 @@
 	static int fd;
 	int n;
 	register char *scan;
-	static int len = 0;
+	static size_t len = 0;
 	static int did_newline = FALSE;
 	int newfile;
 	struct stat sbuf;
diff -ur gawk-3.1.1.orig/awk.h gawk-3.1.1/awk.h
--- gawk-3.1.1.orig/awk.h	Tue Apr 16 13:40:18 2002
+++ gawk-3.1.1/awk.h	Wed May 22 10:49:24 2002
@@ -922,7 +922,7 @@
 extern int os_is_setuid P((void));
 extern int os_setbinmode P((int fd, int mode));
 extern void os_restore_mode P((int fd));
-extern int optimal_bufsize P((int fd, struct stat *sbuf));
+extern size_t optimal_bufsize P((int fd, struct stat *sbuf));
 extern int ispath P((const char *file));
 extern int isdirpunct P((int c));
 /* io.c */
diff -ur gawk-3.1.1.orig/pc/gawkmisc.pc gawk-3.1.1/pc/gawkmisc.pc
--- gawk-3.1.1.orig/pc/gawkmisc.pc	Tue Apr 16 13:58:11 2002
+++ gawk-3.1.1/pc/gawkmisc.pc	Wed May 22 10:51:27 2002
@@ -103,7 +103,7 @@
 
 /* optimal_bufsize --- determine optimal buffer size */
 
-int
+size_t
 optimal_bufsize(fd, stb)
 int fd;
 struct stat *stb;
diff -ur gawk-3.1.1.orig/posix/gawkmisc.c gawk-3.1.1/posix/gawkmisc.c
--- gawk-3.1.1.orig/posix/gawkmisc.c	Tue Apr 16 13:58:41 2002
+++ gawk-3.1.1/posix/gawkmisc.c	Wed May 22 10:50:21 2002
@@ -62,7 +62,7 @@
 
 /* optimal_bufsize --- determine optimal buffer size */
 
-int
+size_t
 optimal_bufsize(fd, stb)
 int fd;
 struct stat *stb;
diff -ur gawk-3.1.1.orig/unsupported/atari/gawkmisc.atr gawk-3.1.1/unsupported/atari/gawkmisc.atr
--- gawk-3.1.1.orig/unsupported/atari/gawkmisc.atr	Thu Aug 16 11:07:48 2001
+++ gawk-3.1.1/unsupported/atari/gawkmisc.atr	Wed May 22 10:51:58 2002
@@ -79,7 +79,7 @@
 
 /* optimal_bufsize --- determine optimal buffer size */
 
-int
+size_t
 optimal_bufsize(fd, stb)
 int fd;
 struct stat *stb;
diff -ur gawk-3.1.1.orig/unsupported/tandem/tmisc.c gawk-3.1.1/unsupported/tandem/tmisc.c
--- gawk-3.1.1.orig/unsupported/tandem/tmisc.c	Sun Jan 28 14:49:25 2001
+++ gawk-3.1.1/unsupported/tandem/tmisc.c	Wed May 22 10:52:31 2002
@@ -90,7 +90,7 @@
 
 /* optimal_bufsize --- determine optimal buffer size */
 
-int
+size_t
 optimal_bufsize(fd, stb)
 int fd;
 struct stat *stb;
diff -ur gawk-3.1.1.orig/vms/gawkmisc.vms gawk-3.1.1/vms/gawkmisc.vms
--- gawk-3.1.1.orig/vms/gawkmisc.vms	Sun Jan 28 14:49:25 2001
+++ gawk-3.1.1/vms/gawkmisc.vms	Wed May 22 10:51:47 2002
@@ -70,7 +70,7 @@
 
 /* optimal_bufsize --- determine optimal buffer size */
 
-int
+size_t
 optimal_bufsize(fd, stb)
 int fd;
 struct stat *stb;
--- gawk-3.1.1.orig/awkgram.c	Tue Apr 16 14:02:08 2002
+++ gawk-3.1.1/awkgram.c	Wed May 22 11:33:15 2002
@@ -2705,7 +2705,7 @@
 	static int fd;
 	int n;
 	register char *scan;
-	static int len = 0;
+	static size_t len = 0;
 	static int did_newline = FALSE;
 	int newfile;
 	struct stat sbuf;