wyhashmap example

misc/wyhashmap.cpp

@@ -0,0 +1,68 @@
+#include <stdint.h>
+#include <stdio.h>
+#include <iostream>
+#include <vector>
+#include "wyhash.h"
+
+/*  This is world's fastest hash map: 2x faster than bytell_hash_map.
+    It does not store the keys, but only the hash/signature of keys.
+    First we use pos=hash1(key) to approximately locate the bucket.
+    Then we search signature=hash2(key) from pos linearly.
+    If we find a bucket with matched signature we report the bucket
+    Or if we meet a bucket whose signature=0, we report a new position to insert
+    The signature collision probability is very low as we usually searched N~10 buckets.
+    By combining hash1 and hash2, we acturally have 128 bit anti-collision strength.
+    hash1 and hash2 can be the same function, resulting lower collision resistance but faster.
+    The signature is 64 bit, but can be modified to 32 bit if necessary for save space.
+    The above two can be activated by define WYHASHMAP_WEAK_SMALL_FAST
+    simple examples:
+*/
+
+#ifdef WYHASHMAP_WEAK_SMALL_FAST // for small hashmaps whose size < 2^24 and acceptable collision
+typedef uint32_t wyhashmap_t;
+#else
+typedef uint64_t wyhashmap_t;
+#endif
+
+///static inline size_t wyhashmap(wyhashmap_t *idx, size_t idx_size, const void *key, size_t key_size, uint8_t insert, uint64_t *secret){
+static inline size_t wyhashmap(wyhashmap_t *idx, size_t idx_size, const void *key, size_t key_size, uint8_t insert, const uint64_t secret[]){
+    size_t i=1; uint64_t h2; wyhashmap_t sig;
+    do{ sig=h2=wyhash(key,key_size,i,secret); i++; }while(_unlikely_(!sig));
+#ifdef WYHASHMAP_WEAK_SMALL_FAST
+    size_t i0=wy2u0k(h2,idx_size);
+#else
+    size_t i0=wy2u0k(wyhash(key,key_size,0,secret),idx_size);
+#endif
+    for(i=i0; i<idx_size&&idx[i]&&idx[i]!=sig; i++);
+    if(_unlikely_(i==idx_size)){
+        for(i=0; i<i0&&idx[i]&&idx[i]!=sig;  i++);
+        if(i==i0) return idx_size;
+    }
+    if(!idx[i]){
+        if(insert) idx[i]=sig;
+        else return idx_size;
+    }
+    return i;
+}
+//#endif
+
+#if 1 //WYHASHMAP_TEST
+int main()
+{
+    const size_t size = 213432;
+    std::vector<wyhashmap_t> idx(size); // allocate the index of fixed size. idx MUST be zeroed.
+    std::vector<value_class> value(size); // we only care about the index, user should maintain his own value vectors.
+    std::string key = "dhskfhdsj"; // the object to be inserted into idx
+    size_t pos = wyhashmap(idx.data(), idx.size(), key.c_str(), key.size(), 1, _wyp); // get the position and insert
+    if(pos<size)
+        value[pos]++; // we process the vallue
+    else
+        std::cerr<<"map is full\n";
+    pos = wyhashmap(idx.data(), idx.size(), key.c_str(), key.size(), 0, _wyp); // just lookup by setting insert=0
+    if(pos<size)
+        value[pos]++; // we process the vallue
+    else
+        std::cerr<<"the key does not exist\n";
+}
+#endif /* WYHASHMAP_TEST */
+