Happy new year!

[xonotic/gmqcc.git] / stat.c

diff --git a/stat.c b/stat.c
index 6987cf7b40a2f376f1bc6ac37dfe1ef3c49fe07d..24a3466a16e9c7f4f83b3354b157bb5bbb778aeb 100644 (file)
--- a/stat.c
+++ b/stat.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2012, 2013
+ * Copyright (C) 2012, 2013, 2014
  *     Dale Weiler
  *     Wolfgang Bumiller
  *
@@ -353,139 +353,11 @@ typedef struct hash_node_t {
     struct hash_node_t *next;  /* next node (linked list)        */
 } hash_node_t;
 
-/*
- * This is a patched version of the Murmur2 hashing function to use
- * a proper pre-mix and post-mix setup. Infact this is Murmur3 for
- * the most part just reinvented.
- *
- * Murmur 2 contains an inner loop such as:
- * while (l >= 4) {
- *      u32 k = *(u32*)d;
- *      k *= m;
- *      k ^= k >> r;
- *      k *= m;
- *
- *      h *= m;
- *      h ^= k;
- *      d += 4;
- *      l -= 4;
- * }
- *
- * The two u32s that form the key are the same value x (pulled from data)
- * this premix stage will perform the same results for both values. Unrolled
- * this produces just:
- *  x *= m;
- *  x ^= x >> r;
- *  x *= m;
- *
- *  h *= m;
- *  h ^= x;
- *  h *= m;
- *  h ^= x;
- *
- * This appears to be fine, except what happens when m == 1? well x
- * cancels out entierly, leaving just:
- *  x ^= x >> r;
- *  h ^= x;
- *  h ^= x;
- *
- * So all keys hash to the same value, but how often does m == 1?
- * well, it turns out testing x for all possible values yeilds only
- * 172,013,942 unique results instead of 2^32. So nearly ~4.6 bits
- * are cancelled out on average!
- *
- * This means we have a 14.5% (rounded) chance of colliding more, which
- * results in another bucket/chain for the hashtable.
- *
- * We fix it buy upgrading the pre and post mix ssystems to align with murmur
- * hash 3.
- */
-#if 1
-#define GMQCC_ROTL32(X, R) (((X) << (R)) | ((X) >> (32 - (R))))
-GMQCC_INLINE size_t util_hthash(hash_table_t *ht, const char *key) {
-    const unsigned char *data   = (const unsigned char *)key;
-    const size_t         len    = strlen(key);
-    const size_t         block  = len / 4;
-    const uint32_t       mask1  = 0xCC9E2D51;
-    const uint32_t       mask2  = 0x1B873593;
-    const uint32_t      *blocks = (const uint32_t*)(data + block * 4);
-    const unsigned char *tail   = (const unsigned char *)(data + block * 4);
-
-    size_t   i;
-    uint32_t k;
-    uint32_t h = 0x1EF0 ^ len;
-
-    for (i = -((int)block); i; i++) {
-        k  = blocks[i];
-        k *= mask1;
-        k  = GMQCC_ROTL32(k, 15);
-        k *= mask2;
-        h ^= k;
-        h  = GMQCC_ROTL32(h, 13);
-        h  = h * 5 + 0xE6546B64;
-    }
 
-    k = 0;
-    switch (len & 3) {
-        case 3:
-            k ^= tail[2] << 16;
-        case 2:
-            k ^= tail[1] << 8;
-        case 1:
-            k ^= tail[0];
-            k *= mask1;
-            k  = GMQCC_ROTL32(k, 15);
-            k *= mask2;
-            h ^= k;
-    }
-
-    h ^= len;
-    h ^= h >> 16;
-    h *= 0x85EBCA6B;
-    h ^= h >> 13;
-    h *= 0xC2B2AE35;
-    h ^= h >> 16;
-
-    return (size_t) (h % ht->size);
+size_t hash(const char *key);
+size_t util_hthash(hash_table_t *ht, const char *key) {
+    return hash(key) % ht->size;
 }
-#undef GMQCC_ROTL32
-#else
-/* We keep the old for reference */
-GMQCC_INLINE size_t util_hthash(hash_table_t *ht, const char *key) {
-    const uint32_t       mix   = 0x5BD1E995;
-    const uint32_t       rot   = 24;
-    size_t               size  = strlen(key);
-    uint32_t             hash  = 0x1EF0 /* LICRC TAB */  ^ size;
-    uint32_t             alias = 0;
-    const unsigned char *data  = (const unsigned char*)key;
-
-    while (size >= 4) {
-        alias  = (data[0] | (data[1] << 8) | (data[2] << 16) | (data[3] << 24));
-        alias *= mix;
-        alias ^= alias >> rot;
-        alias *= mix;
-
-        hash  *= mix;
-        hash  ^= alias;
-
-        data += 4;
-        size -= 4;
-    }
-
-    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 (size_t) (hash % ht->size);
-}
-#endif
 
 static hash_node_t *_util_htnewpair(const char *key, void *value) {
     hash_node_t *node;