comparison: docs/Writerside/topics/hash_key.h.md
docs/Writerside/topics/hash_key.h.md
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- docs/3.1
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- 1a8fe7b7dd8a
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| 1144:b23d07fff6ca | 1145:1a8fe7b7dd8a |
|---|---|
| 1 # Hash Function | 1 # Hash Function |
| 2 | 2 |
| 3 UCX implements the MurmurHash2 algorithm for computing hashes that are primarily used for [CxMap](map.h.md). | 3 UCX implements the MurmurHash2 algorithm for computing hashes that are primarily used for [CxMap](map.h.md). |
| 4 But it can be used for arbitrary custom scenarios, too. | 4 But it can be used for arbitrary custom scenarios, too. |
| 5 | 5 |
| 6 There are four functions which all generate a `CxHashKey` structure for given data. | 6 ## Overview |
| 7 ```C | |
| 8 #include <cx/hash_key.h> | |
| 7 | 9 |
| 8 * `cx_hash_key()` takes an arbitrary pointer and a length | 10 void cx_hash_murmur(CxHashKey *key); |
| 9 * `cx_hash_key_bytes()` takes an `unsigned char*` and a length | 11 CxHashKey cx_hash_key(const void *obj, size_t len); |
| 10 * `cx_hash_key_str()` takes a usual C string | 12 CxHashKey cx_hash_key_str(const char *str); |
| 11 * `cx_hash_key_cxstr()` takes a [UCX string](string.h.md) | 13 CxHashKey cx_hash_key_bytes(const unsigned char *bytes, size_t len); |
| 14 CxHashKey cx_hash_key_cxstr(cxstring str); | |
| 15 ``` | |
| 12 | 16 |
| 13 The hash is then available in the `hash` field of the returned structure. | 17 ## Description |
| 18 | |
| 19 The primary function for creating a `CxHashKey` structure is `cx_hash_key()`. | |
| 20 The other functions do effectively the same, but | |
| 21 | |
| 22 * `cx_hash_key_bytes()` is strongly typed if you want to avoid passing `void*` | |
| 23 * `cx_hash_key_str()` conveniently takes a C string and computes the length on its own | |
| 24 * `cx_hash_key_cxstr()` conveniently takes a [UCX string](string.h.md) | |
| 25 | |
| 26 In all cases, the hash will be available in the `hash` field of the returned structure. | |
| 14 | 27 |
| 15 <note> | 28 <note> |
| 16 UCX assigns the hash value <code>1574210520</code> to the <code>NULL</code> pointer. | 29 UCX assigns the hash value <code>1574210520</code> to the <code>NULL</code> pointer. |
| 17 This is a careful choice which is not standard MurmurHash2 and an extension to support <code>NULL</code> pointers. | 30 This is a careful choice which is not standard MurmurHash2 and an extension to support <code>NULL</code> pointers. |
| 18 </note> | 31 </note> |
| 27 CxHashKey key; | 40 CxHashKey key; |
| 28 key.data = mystring; | 41 key.data = mystring; |
| 29 key.len = strlen(mystring); | 42 key.len = strlen(mystring); |
| 30 cx_hash_murmur(&key); | 43 cx_hash_murmur(&key); |
| 31 ``` | 44 ``` |
| 45 | |
| 46 <seealso> | |
| 47 <category ref="apidoc"> | |
| 48 <a href="https://ucx.sourceforge.io/api/hash__key_8h.html">hash_key.h</a> | |
| 49 </category> | |
| 50 </seealso> |
