commit 1765f0ae0b8932a4977c181c07d174f124143cef
from: Florian Westphal <fw@strlen.de>
date: Sun Jun 26 22:16:37 2011 UTC

hash: use more recent lookup3 algorithm instead of lookup2

Bob Jenkins published a newer hash function in May 2006, it has
better distribution.

See http://burtleburtle.net/bob/hash/doobs.html for lengthy
comparisions.

commit - 7f8d0ea5a3e927b8b6dd84eae63849ae17cdf5ae
commit + 1765f0ae0b8932a4977c181c07d174f124143cef
blob - 113133d20c7f75019b35297aba13904cf32e4c79
blob + 7b7976c9a330ac29e63135215ba96429e4f02505
--- src/ngircd/hash.c
+++ src/ngircd/hash.c
@@ -26,8 +26,7 @@
 #include "exp.h"
 #include "hash.h"
 
-static UINT32 jenkins_hash PARAMS((register UINT8 *k, register UINT32 length,
-				   register UINT32 initval));
+static UINT32 jenkins_hash PARAMS((UINT8 *k, UINT32 length, UINT32 initval));
 
 /**
  * Calculate hash value for a given string.
@@ -46,66 +45,74 @@ Hash( const char *String )
 } /* Hash */
 
 /*
- * This hash function originates from lookup2.c of Bob Jenkins
- * (URL: <http://burtleburtle.net/bob/c/lookup2.c>):
+ * This hash function originates from lookup3.c of Bob Jenkins
+ * (URL: <http://burtleburtle.net/bob/c/lookup3.c>):
  * --------------------------------------------------------------------
- * 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.
+ * lookup3.c, by Bob Jenkins, May 2006, Public Domain.
+ * These are functions for producing 32-bit hashes for hash table lookup.
+ * hashword(), hashlittle(), hashlittle2(), hashbig(), mix(), and final()
+ * 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's in
+ * the public domain.  It has no warranty.
  * --------------------------------------------------------------------
  * Not all of his functions are used here.
  */
 
-#define hashsize(n) ((UINT32)1<<(n))
+#define hashsize(n) ((uint32_t)1<<(n))
 #define hashmask(n) (hashsize(n)-1)
+#define rot(x,k) (((x)<<(k)) | ((x)>>(32-(k))))
 
 #define 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); \
+	a -= c;  a ^= rot(c, 4);  c += b; \
+	b -= a;  b ^= rot(a, 6);  a += c; \
+	c -= b;  c ^= rot(b, 8);  b += a; \
+	a -= c;  a ^= rot(c,16);  c += b; \
+	b -= a;  b ^= rot(a,19);  a += c; \
+	c -= b;  c ^= rot(b, 4);  b += a; \
 } /* mix */
 
+#define final(a,b,c) \
+{ \
+	c ^= b; c -= rot(b,14); \
+	a ^= c; a -= rot(c,11); \
+	b ^= a; b -= rot(a,25); \
+	c ^= b; c -= rot(b,16); \
+	a ^= c; a -= rot(c,4);  \
+	b ^= a; b -= rot(a,14); \
+	c ^= b; c -= rot(b,24); \
+}
+
 static UINT32
-jenkins_hash( register UINT8 *k, register UINT32 length, register UINT32 initval )
+jenkins_hash(UINT8 *k, UINT32 length, UINT32 initval)
 {
 	/* k: the key
 	 * length: length of the key
 	 * initval: the previous hash, or an arbitrary value
 	 */
+	UINT32 a,b,c;
 
-	register UINT32 a,b,c,len;
-
 	/* Set up the internal state */
-	len = length;
-	a = b = 0x9e3779b9;	/* the golden ratio; an arbitrary value */
-	c = initval;		/* the previous hash value */
+	a = b = c = 0xdeadbeef + length + initval;
 
 	/* handle most of the key */
-	while (len >= 12)
-	{
+	while (length > 12) {
 		a += (k[0] +((UINT32)k[1]<<8) +((UINT32)k[2]<<16) +((UINT32)k[3]<<24));
 		b += (k[4] +((UINT32)k[5]<<8) +((UINT32)k[6]<<16) +((UINT32)k[7]<<24));
 		c += (k[8] +((UINT32)k[9]<<8) +((UINT32)k[10]<<16)+((UINT32)k[11]<<24));
 		mix(a,b,c);
-		k += 12; len -= 12;
+		length -= 12;
+		k += 12;
 	}
 
-	/* handle the last 11 bytes */
-	c += length;
-	switch( (int)len )	/* all the case statements fall through */
+	/*-------------------------------- last block: affect all 32 bits of (c) */
+	switch(length)                   /* all the case statements fall through */
+
 	{
-		case 11: c+=((UINT32)k[10]<<24);
-		case 10: c+=((UINT32)k[9]<<16);
-		case 9 : c+=((UINT32)k[8]<<8);
-		/* the first byte of c is reserved for the length */
+		case 12: c+=((UINT32)k[11])<<24;
+		case 11: c+=((UINT32)k[10]<<16);
+		case 10: c+=((UINT32)k[9]<<8);
+		case 9 : c+=k[8];
 		case 8 : b+=((UINT32)k[7]<<24);
 		case 7 : b+=((UINT32)k[6]<<16);
 		case 6 : b+=((UINT32)k[5]<<8);
@@ -114,11 +121,10 @@ jenkins_hash( register UINT8 *k, register UINT32 lengt
 		case 3 : a+=((UINT32)k[2]<<16);
 		case 2 : a+=((UINT32)k[1]<<8);
 		case 1 : a+=k[0];
-		/* case 0: nothing left to add */
+			 break;
+		case 0 : return c;
 	}
-	mix(a,b,c);
-
-	/* report the result */
+	final(a,b,c);
 	return c;
 } /* jenkins_hash */