Slightly more cache-friendly hashing (WIP)

src/common/kernel/eressea.c

@@ -633,40 +633,6 @@ shipspeed (const ship * sh, const unit * u)
   return k;
 }
 
-/* erwartete Anzahl Einheiten x 2 */
-#define UMAXHASH 199999
-unit *unithash[UMAXHASH];
-
-void
-uhash (unit * u)
-{
-  assert(!u->nexthash || !"unit ist bereits gehasht");
-  u->nexthash = unithash[u->no % UMAXHASH];
-  unithash[u->no % UMAXHASH] = u;
-}
-
-void
-uunhash (unit * u)
-{
-  unit ** x = &(unithash[u->no % UMAXHASH]);
-  while (*x && *x!=u) x = &(*x)->nexthash;
-  assert(*x || !"unit nicht gefunden");
-  *x = u->nexthash;
-  u->nexthash=NULL;
-}
-
-unit *
-ufindhash (int i)
-{
-  assert(i>=0);
-  if (i>=0) {
-    unit * u = unithash[i % UMAXHASH];
-    while (u && u->no!=i) u = u->nexthash;
-    return u;
-  }
-  return NULL;
-}
-
 #define FMAXHASH 2039
 faction * factionhash[FMAXHASH];
 
@@ -1438,7 +1404,10 @@ findunitr (const region * r, int n)
 
 unit *findunit(int n)
 {
-  return findunitg(n, NULL);
+  if (n <= 0) {
+    return NULL;
+  }
+  return ufindhash(n);
 }
 
 unit *

src/common/kernel/eressea.h

@@ -39,8 +39,12 @@ extern "C" {
   
 #define ALLIED(f1, f2) (f1==f2 || (f1->alliance && f1->alliance==f2->alliance))
 
+/* for some good prime numbers, check http://www.math.niu.edu/~rusin/known-math/98/pi_x */
 #ifndef MAXREGIONS
-# define MAXREGIONS 262139 /* must be prime for hashing. 262139=last<2^18 */
+# define MAXREGIONS 262139 /* must be prime for hashing. */
+#endif
+#ifndef MAXUNITS
+# define MAXUNITS 524287 /* must be prime for hashing. */
 #endif
 
 #define MONSTER_FACTION 0 /* Die Partei, in der die Monster sind. */
@@ -274,11 +278,6 @@ void changeblockchaos(void);
 extern struct region *firstregion(struct faction * f);
 extern struct region *lastregion(struct faction * f);
 
-void inituhash(void);
-void uhash(struct unit * u);
-void uunhash(struct unit * u);
-struct unit *ufindhash(int i);
-
 void fhash(struct faction * f);
 void funhash(struct faction * f);
 

src/common/kernel/unit.c

@@ -67,6 +67,92 @@ attrib_type at_creator = {
     /* Rest ist NULL; temporäres, nicht alterndes Attribut */
 };
 
+#define UMAXHASH MAXUNITS
+static unit * unithash[UMAXHASH];
+static unit * delmarker = (unit*)unithash; /* a funny hack */
+
+#define HASH_STATISTICS 1
+#if HASH_STATISTICS
+static int hash_requests;
+static int hash_misses;
+#endif
+
+/* benchmark: 
+ * jenkins_hash: 5.25 misses/hit
+ * wang_hash:    5.33 misses/hit
+ */
+
+INLINE_FUNCTION unsigned int jenkins_hash(unsigned int a)
+{
+  a = (a+0x7ed55d16) + (a<<12);
+  a = (a^0xc761c23c) ^ (a>>19);
+  a = (a+0x165667b1) + (a<<5);
+  a = (a+0xd3a2646c) ^ (a<<9);
+  a = (a+0xfd7046c5) + (a<<3);
+  a = (a^0xb55a4f09) ^ (a>>16);
+  return a;
+}
+
+INLINE_FUNCTION unsigned int wang_hash(unsigned int a)
+{
+  a = ~a + (a << 15); // a = (a << 15) - a - 1;
+  a = a ^ (a >> 12);
+  a = a + (a << 2);
+  a = a ^ (a >> 4);
+  a = a * 2057; // a = (a + (a << 3)) + (a << 11);
+  a = a ^ (a >> 16);
+  return a;
+}
+
+#define HASH1(a, m) (jenkins_hash(a) % m)
+#define HASH2(a, m) 1
+/*
+#define HASH1(a, m) ((a) % m)
+#define HASH2(a, m) (m - 2 - a % (m-2))
+*/
+
+void
+uhash(unit * u)
+{
+  int key = HASH1(u->no, UMAXHASH), gk = HASH2(u->no, UMAXHASH);
+  while (unithash[key]!=NULL && unithash[key]!=delmarker && unithash[key]!=u) {
+    key = (key + gk) % UMAXHASH;
+  }
+  assert(unithash[key]!=u || !"trying to add the same unit twice");
+  unithash[key] = u;
+}
+
+void
+uunhash(unit * u)
+{
+  int key = HASH1(u->no, UMAXHASH), gk = HASH2(u->no, UMAXHASH);
+  while (unithash[key]!=NULL && unithash[key]!=u) {
+    key = (key + gk) % UMAXHASH;
+  }
+  assert(unithash[key]==u || !"trying to remove a unit that is not hashed");
+  unithash[key] = delmarker;
+}
+
+unit *
+ufindhash(int uid)
+{
+  assert(uid>=0);
+#if HASH_STATISTICS
+  ++hash_requests;
+#endif
+  if (uid>=0) {
+    int key = HASH1(uid, UMAXHASH), gk = HASH2(uid, UMAXHASH);
+    while (unithash[key]!=NULL && (unithash[key]==delmarker || unithash[key]->no!=uid)) {
+      key = (key + gk) % UMAXHASH;
+#if HASH_STATISTICS
+      ++hash_misses;
+#endif
+    }
+    return unithash[key];
+  }
+  return NULL;
+}
+
 #define DMAXHASH 7919
 typedef struct dead {
   struct dead * nexthash;

src/common/kernel/unit.h

@@ -77,7 +77,6 @@ extern int countheroes(const struct faction * f);
 
 typedef struct unit {
   struct unit *next; /* needs to be first entry, for region's unitlist */
-	struct unit *nexthash;
   struct unit *nextF; /* nächste Einheit der Partei */
   struct region *region;
   int no;
@@ -217,6 +216,10 @@ extern void stripunit(struct unit * u);
 extern void name_unit(struct unit *u);
 extern struct unit * create_unit(struct region * r1, struct faction * f, int number, const struct race * rc, int id, const char * dname, struct unit *creator);
 
+extern void uhash(struct unit * u);
+extern void uunhash(struct unit * u);
+extern struct unit *ufindhash(int i);
+
 extern struct attrib_type at_creator;
 #ifdef __cplusplus
 }