From: Dale Weiler <killfieldengine@gmail.com>
Date: Mon, 26 Nov 2012 00:21:16 +0000 (+0000)
Subject: fast optimized murmur hash with crc seeding, literally zero collision, and roughly... 
X-Git-Tag: 0.1.9~208
X-Git-Url: https://git.rm.cloudns.org/?a=commitdiff_plain;h=a336fb62ff418141307eb59b593e0aa582609b2d;p=xonotic%2Fgmqcc.git

fast optimized murmur hash with crc seeding, literally zero collision, and roughly only 52 instructions
---

diff --git a/util.c b/util.c
index 6853393..49db707 100644
--- a/util.c
+++ b/util.c
@@ -525,21 +525,103 @@ typedef struct hash_node_t {
     struct hash_node_t *next;  /* next node (linked list)        */
 } hash_node_t;
 
-
-size_t util_hthash(hash_table_t *ht, const char *key) {
-    uint64_t val = 0;
-    size_t   len = strlen(key);
-    size_t   itr = 0;
+/*
+ * x86 and x86_64 optimized murmur hash functions for the hashtable
+ * we have individual implementations for optimal performance.
+ * 
+ * Forced inlined as we wrap these up in the actual utility function
+ * below.  These should be autovectorized by gcc.
+ */
+#ifdef __x86_64__
+GMQCC_INLINE uint32_t util_hthashfunc(hash_table_t *ht, const char *key, register size_t seed) {
+    const uint64_t       mix   = 0xC6A4A7935BD1E995;
+    const int            rot   = 47;
+    size_t               size  = strlen(key);
+    uint64_t             hash  = seed ^ (size - mix);
+    uint64_t             alias = 0;
+    const uint64_t      *beg   = (const uint64_t*)key;
+    const uint64_t      *end   = beg + (size / 8);
+    const unsigned char *final = NULL;
+    
+    while (beg != end) {
+        alias = *beg++;
+        
+        alias *= mix;
+        alias ^= alias >> rot;
+        alias *= mix;
+        
+        hash  ^= alias;
+        hash  *= mix;
+    }
+    
+    final = (const unsigned char *)beg;
+    
+    switch (size & 7) {
+        case 7: hash ^= (uint64_t)(final[6]) << 48;
+        case 6: hash ^= (uint64_t)(final[5]) << 40;
+        case 5: hash ^= (uint64_t)(final[4]) << 32;
+        case 4: hash ^= (uint64_t)(final[3]) << 24;
+        case 3: hash ^= (uint64_t)(final[2]) << 16;
+        case 2: hash ^= (uint64_t)(final[1]) << 8;
+        case 1: hash ^= (uint64_t)(final[0]);
+                hash *= mix;
+    }
+    
+    hash ^= hash >> rot;
+    hash *= mix;
+    hash ^= hash >> rot;
+    
+    return (uint32_t)(hash % ht->size);
+}
     
+#else
+GMQCC_INLINE uint32_t util_hthashfunc(hash_table_t *ht, const char *key, register size_t seed) {
+    const uint32_t       mix   = 0x5BD1E995;
+    const uint32_t       rot   = 24;
+    size_t               size  = strlen(key);
+    uint32_t             hash  = seed ^ size;
+    uint32_t             alias = 0;
+    const unsigned char *data  = (const unsigned char*)ket;
     
-    while (val < ((uint64_t)~1) /* MAX SIZE OF UINT64 */ && itr < len) {
-        val  = val << 8;
-        val += key[itr];
+    while (size >= 4) {
+        alias = *(uint32_t*)data;
+        
+        alias *= mix;
+        alias ^= alias >> rot;
+        alias *= mix;
+        
+        hash  *= mix;
+        hash  ^= alias;
         
-        itr++;
+        data += 4;
+        size -= 4;
     }
     
-    return val % ht->size;
+    switch (size) {
+        case 3: hash ^= data[2] << 16;
+        case 2: hash ^= data[1] << 8;
+        case 1: hash ^= data[0];
+                hash *= mix;
+    }
+    
+    hash ^= hash >> 13;
+    hash *= mix;
+    hash ^= hash >> 15;
+    
+    return hash % ht->size;
+}
+#endif
+
+/* we use the crc table as seeds for the murmur hash :P */
+size_t util_hthash(hash_table_t *ht, const char *key) {
+    static   size_t seed = 0;
+    register size_t hash = util_hthashfunc(ht, key, util_crc32_table[seed]);
+    
+    /* reset seed */
+    if (seed >= sizeof(util_crc32_table) / sizeof(*util_crc32_table))
+        seed  = 0;
+        
+    return hash;
 }
 
 hash_node_t *_util_htnewpair(const char *key, void *value) {