2004-07-09 Paul Jakma <paul@dishone.st>

        * jhash.{c,h}: New files. Bob Jenkins' public domain hashing
          function, as implemented in linux kernel by David Miller.

1 files changed, 170 insertions, 0 deletions

diff --git a/lib/jhash.c b/lib/jhash.c
new file mode 100644
index 00000000..071fed6e
--- /dev/null
+++ b/lib/jhash.c
@@ -0,0 +1,170 @@
+/* jhash.h: Jenkins hash support.
+ *
+ * Copyright (C) 1996 Bob Jenkins (bob_jenkins@burtleburtle.net)
+ *
+ * http://burtleburtle.net/bob/hash/
+ *
+ * These are the credits from Bob's sources:
+ *
+ * lookup2.c, by Bob Jenkins, December 1996, Public Domain.
+ * hash(), hash2(), hash3, and mix() are externally useful functions.
+ * Routines to test the hash are included if SELF_TEST is defined.
+ * You can use this free for any purpose.  It has no warranty.
+ *
+ * Copyright (C) 2003 David S. Miller (davem@redhat.com)
+ *
+ * I've modified Bob's hash to be useful in the Linux kernel, and
+ * any bugs present are surely my fault.  -DaveM
+ */
+
+#include "zebra.h"
+#include "jhash.h"
+
+/* The golden ration: an arbitrary value */
+#define JHASH_GOLDEN_RATIO  0x9e3779b9
+
+/* NOTE: Arguments are modified. */
+#define __jhash_mix(a, b, c) \
+{ \
+  a -= b; a -= c; a ^= (c>>13); \
+  b -= c; b -= a; b ^= (a<<8); \
+  c -= a; c -= b; c ^= (b>>13); \
+  a -= b; a -= c; a ^= (c>>12);  \
+  b -= c; b -= a; b ^= (a<<16); \
+  c -= a; c -= b; c ^= (b>>5); \
+  a -= b; a -= c; a ^= (c>>3);  \
+  b -= c; b -= a; b ^= (a<<10); \
+  c -= a; c -= b; c ^= (b>>15); \
+}
+
+/* The most generic version, hashes an arbitrary sequence
+ * of bytes.  No alignment or length assumptions are made about
+ * the input key.
+ */
+u_int32_t
+jhash (void *key, u_int32_t length, u_int32_t initval)
+{
+  u_int32_t a, b, c, len;
+  u_int8_t *k = key;
+
+  len = length;
+  a = b = JHASH_GOLDEN_RATIO;
+  c = initval;
+
+  while (len >= 12)
+    {
+      a +=
+        (k[0] + ((u_int32_t) k[1] << 8) + ((u_int32_t) k[2] << 16) +
+         ((u_int32_t) k[3] << 24));
+      b +=
+        (k[4] + ((u_int32_t) k[5] << 8) + ((u_int32_t) k[6] << 16) +
+         ((u_int32_t) k[7] << 24));
+      c +=
+        (k[8] + ((u_int32_t) k[9] << 8) + ((u_int32_t) k[10] << 16) +
+         ((u_int32_t) k[11] << 24));
+
+      __jhash_mix (a, b, c);
+
+      k += 12;
+      len -= 12;
+    }
+
+  c += length;
+  switch (len)
+    {
+    case 11:
+      c += ((u_int32_t) k[10] << 24);
+    case 10:
+      c += ((u_int32_t) k[9] << 16);
+    case 9:
+      c += ((u_int32_t) k[8] << 8);
+    case 8:
+      b += ((u_int32_t) k[7] << 24);
+    case 7:
+      b += ((u_int32_t) k[6] << 16);
+    case 6:
+      b += ((u_int32_t) k[5] << 8);
+    case 5:
+      b += k[4];
+    case 4:
+      a += ((u_int32_t) k[3] << 24);
+    case 3:
+      a += ((u_int32_t) k[2] << 16);
+    case 2:
+      a += ((u_int32_t) k[1] << 8);
+    case 1:
+      a += k[0];
+    };
+
+  __jhash_mix (a, b, c);
+
+  return c;
+}
+
+/* A special optimized version that handles 1 or more of u_int32_ts.
+ * The length parameter here is the number of u_int32_ts in the key.
+ */
+u_int32_t
+jhash2 (u_int32_t * k, u_int32_t length, u_int32_t initval)
+{
+  u_int32_t a, b, c, len;
+
+  a = b = JHASH_GOLDEN_RATIO;
+  c = initval;
+  len = length;
+
+  while (len >= 3)
+    {
+      a += k[0];
+      b += k[1];
+      c += k[2];
+      __jhash_mix (a, b, c);
+      k += 3;
+      len -= 3;
+    }
+
+  c += length * 4;
+
+  switch (len)
+    {
+    case 2:
+      b += k[1];
+    case 1:
+      a += k[0];
+    };
+
+  __jhash_mix (a, b, c);
+
+  return c;
+}
+
+
+/* A special ultra-optimized versions that knows they are hashing exactly
+ * 3, 2 or 1 word(s).
+ *
+ * NOTE: In partilar the "c += length; __jhash_mix(a,b,c);" normally
+ *       done at the end is not done here.
+ */
+u_int32_t
+jhash_3words (u_int32_t a, u_int32_t b, u_int32_t c, u_int32_t initval)
+{
+  a += JHASH_GOLDEN_RATIO;
+  b += JHASH_GOLDEN_RATIO;
+  c += initval;
+
+  __jhash_mix (a, b, c);
+
+  return c;
+}
+
+u_int32_t
+jhash_2words (u_int32_t a, u_int32_t b, u_int32_t initval)
+{
+  return jhash_3words (a, b, 0, initval);
+}
+
+u_int32_t
+jhash_1word (u_int32_t a, u_int32_t initval)
+{
+  return jhash_3words (a, 0, 0, initval);
+}