2001-09-20 Benjamin Kosnik <bkoz@redhat.com>

[pf3gnuchains/gcc-fork.git] / libiberty / hashtab.c

diff --git a/libiberty/hashtab.c b/libiberty/hashtab.c
index 97b717f..89bfe08 100644 (file)
--- a/libiberty/hashtab.c
+++ b/libiberty/hashtab.c
@@ -71,14 +71,6 @@ static PTR *find_empty_slot_for_expand  PARAMS ((htab_t, hashval_t));
 htab_hash htab_hash_pointer = hash_pointer;
 htab_eq htab_eq_pointer = eq_pointer;
 
-/* This avoids a warning that 4294967291 is signed for pre-ISO C systems and
-   unsigned for ISO C systems on 32-bit hosts.  */
-#ifdef __STDC__
-#define UL(num) num ## UL
-#else
-#define UL(num) ((unsigned long)(num/**/L))
-#endif
-
 /* The following function returns a nearest prime number which is
    greater than N, and near a power of two. */
 
@@ -89,37 +81,38 @@ higher_prime_number (n)
   /* These are primes that are near, but slightly smaller than, a
      power of two.  */
   static unsigned long primes[] = {
-    UL(2),
-    UL(7),
-    UL(13),
-    UL(31),
-    UL(61),
-    UL(127),
-    UL(251),
-    UL(509),
-    UL(1021),
-    UL(2039),
-    UL(4093),
-    UL(8191),
-    UL(16381),
-    UL(32749),
-    UL(65521),
-    UL(131071),
-    UL(262139),
-    UL(524287),
-    UL(1048573),
-    UL(2097143),
-    UL(4194301),
-    UL(8388593),
-    UL(16777213),
-    UL(33554393),
-    UL(67108859),
-    UL(134217689),
-    UL(268435399),
-    UL(536870909),
-    UL(1073741789),
-    UL(2147483647),
-    UL(4294967291),
+    (unsigned long) 2,
+    (unsigned long) 7,
+    (unsigned long) 13,
+    (unsigned long) 31,
+    (unsigned long) 61,
+    (unsigned long) 127,
+    (unsigned long) 251,
+    (unsigned long) 509,
+    (unsigned long) 1021,
+    (unsigned long) 2039,
+    (unsigned long) 4093,
+    (unsigned long) 8191,
+    (unsigned long) 16381,
+    (unsigned long) 32749,
+    (unsigned long) 65521,
+    (unsigned long) 131071,
+    (unsigned long) 262139,
+    (unsigned long) 524287,
+    (unsigned long) 1048573,
+    (unsigned long) 2097143,
+    (unsigned long) 4194301,
+    (unsigned long) 8388593,
+    (unsigned long) 16777213,
+    (unsigned long) 33554393,
+    (unsigned long) 67108859,
+    (unsigned long) 134217689,
+    (unsigned long) 268435399,
+    (unsigned long) 536870909,
+    (unsigned long) 1073741789,
+    (unsigned long) 2147483647,
+                                       /* 4294967291L */
+    ((unsigned long) 2147483647) + ((unsigned long) 2147483644),
   };
 
   unsigned long* low = &primes[0];
@@ -568,3 +561,42 @@ htab_collisions (htab)
 
   return (double) htab->collisions / (double) htab->searches;
 }
+
+/* Hash P as a null-terminated string.
+
+   Copied from gcc/hashtable.c.  Zack had the following to say with respect
+   to applicability, though note that unlike hashtable.c, this hash table
+   implementation re-hashes rather than chain buckets.
+
+   http://gcc.gnu.org/ml/gcc-patches/2001-08/msg01021.html
+   From: Zack Weinberg <zackw@panix.com>
+   Date: Fri, 17 Aug 2001 02:15:56 -0400
+
+   I got it by extracting all the identifiers from all the source code
+   I had lying around in mid-1999, and testing many recurrences of
+   the form "H_n = H_{n-1} * K + c_n * L + M" where K, L, M were either
+   prime numbers or the appropriate identity.  This was the best one.
+   I don't remember exactly what constituted "best", except I was
+   looking at bucket-length distributions mostly.
+   
+   So it should be very good at hashing identifiers, but might not be
+   as good at arbitrary strings.
+   
+   I'll add that it thoroughly trounces the hash functions recommended
+   for this use at http://burtleburtle.net/bob/hash/index.html, both
+   on speed and bucket distribution.  I haven't tried it against the
+   function they just started using for Perl's hashes.  */
+
+hashval_t
+htab_hash_string (p)
+     const PTR p;
+{
+  const unsigned char *str = (const unsigned char *) p;
+  hashval_t r = 0;
+  unsigned char c;
+
+  while ((c = *str++) != 0)
+    r = r * 67 + c - 113;
+
+  return r;
+}