hi,
here is a patch for file stolen from FreeBSD.

before:
$ time file /etc/passwd
/etc/passwd: ASCII text
   1.06s real    0.40s user    0.34s system 
after:
$ time file.patched /etc/passwd
/etc/passwd: ASCII text
   0.21s real    0.09s user    0.04s system 

diff -uNr file/apprentice.c file.patched/apprentice.c
--- file/apprentice.c	Sat Sep  4 20:51:09 1999
+++ file.patched/apprentice.c	Sat Sep  4 20:42:17 1999
@@ -56,7 +56,7 @@
 static void eatsize	__P((char **));
 
 static int maxmagic = 0;
-
+static int alloc_incr = 256;
 static int apprentice_1	__P((const char *, int));
 
 int
@@ -189,9 +189,9 @@
 	struct magic *m;
 	char *t, *s;
 
-#define ALLOC_INCR	20
 	if (nd+1 >= maxmagic){
-	    maxmagic += ALLOC_INCR;
+	    maxmagic += alloc_incr;
+
 	    if ((magic = (struct magic *) realloc(magic, 
 						  sizeof(struct magic) * 
 						  maxmagic)) == NULL) {
@@ -201,7 +201,8 @@
 		else
 			exit(1);
 	    }
-	    memset(&magic[*ndx], 0, sizeof(struct magic) * ALLOC_INCR);
+	    memset(&magic[*ndx], 0, sizeof(struct magic) * alloc_incr);
+	    alloc_incr *= 2;
 	}
 	m = &magic[*ndx];
 	m->flag = 0;
diff -uNr file/file.h file.patched/file.h
--- file/file.h	Sat Sep  4 20:51:09 1999
+++ file.patched/file.h	Sat Sep  4 20:33:21 1999
@@ -37,7 +37,7 @@
 #ifndef HOWMANY
 # define HOWMANY 8192		/* how much of the file to look at */
 #endif
-#define MAXMAGIS 1000		/* max entries in /etc/magic */
+#define MAXMAGIS 5000		/* max entries in /etc/magic */
 #define MAXDESC	50		/* max leng of text description */
 #define MAXstring 32		/* max leng of "string" types */