What Is a Hashmap?
A hash table (also called a hash table) is a data structure that is accessed directly according to a key value. That is, it accesses records by mapping key values to a location in the table to speed up lookups. This mapping function is called a hash function, and the array holding the records is called a hash table.
- If the keyword is k , its value is stored in the storage location of f (k) . As a result, the searched records can be obtained directly without comparison. This correspondence relationship f is called a hash function, and the table established according to this idea is a hash table.
- It is possible to get the same hash address for different keywords, that is, k1 k2 , and f (k1) = f (k2) . This phenomenon is called collision. Keywords with the same function value are called synonyms for the hash function. In summary, according to the hash function f (k) and the method of dealing with conflicts, a set of keywords is mapped to a limited continuous address set (interval), and the "image" of the keywords in the address set is used as a record In the storage location of a table, this kind of table is called a hash table. This mapping process is called hash table or hash, and the resulting storage location is called a hash address.
- If for any keyword in the keyword set, the probability that the hash function maps to any address in the address set is equal, such a hash function is called a uniform hash function (Uniform Hash function). Is to make the key through the hash function to get a "random address", thereby reducing conflicts.
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- The above is some basic prerequisite knowledge about hash and its related. So what role does he play in emule?
- Everyone knows that emule is based on P2P (short for Peer-to-peer, which refers to software for peer-to-peer connection), and it uses the "multi-source file transfer protocol" (
- (The famous ELFhash algorithm) [3]
int ELFhash (char * key) { unsigned long h = 0; while (* key) { h = (h << 4) + * key ++; unsigned long g = h & 0xF0000000L; if (g) h ^ = g >> 24; h & = ~ g; } return h% MOD; }