comparison: docs/Writerside/topics/hash_key.h.md
docs/Writerside/topics/hash_key.h.md
- changeset 1409
- 6856869e29f1
- parent 1400
- 7bc88ae62755
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| 1408:aaa440cd4125 | 1409:6856869e29f1 |
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| 12 uint32_t cx_hash_u32(uint32_t x); | 12 uint32_t cx_hash_u32(uint32_t x); |
| 13 uint64_t cx_hash_u64(uint64_t x); | 13 uint64_t cx_hash_u64(uint64_t x); |
| 14 | 14 |
| 15 CxHashKey cx_hash_key(const void *obj, size_t len); | 15 CxHashKey cx_hash_key(const void *obj, size_t len); |
| 16 CxHashKey cx_hash_key_str(const char *str); | 16 CxHashKey cx_hash_key_str(const char *str); |
| 17 CxHashKey cx_hash_key_ustr(const unsigned char *str); | |
| 17 CxHashKey cx_hash_key_bytes(const unsigned char *bytes, size_t len); | 18 CxHashKey cx_hash_key_bytes(const unsigned char *bytes, size_t len); |
| 18 CxHashKey cx_hash_key_cxstr(cxstring str); | 19 CxHashKey cx_hash_key_cxstr(cxstring str); |
| 19 CxHashKey cx_hash_key_u32(uint32_t x); | 20 CxHashKey cx_hash_key_u32(uint32_t x); |
| 20 CxHashKey cx_hash_key_u64(uint64_t x); | 21 CxHashKey cx_hash_key_u64(uint64_t x); |
| 21 | 22 |
| 27 The primary function for creating a `CxHashKey` structure from non-integers is `cx_hash_key()`. | 28 The primary function for creating a `CxHashKey` structure from non-integers is `cx_hash_key()`. |
| 28 The other functions effectively do the same, but | 29 The other functions effectively do the same, but |
| 29 | 30 |
| 30 * `cx_hash_key_bytes()` is strongly typed if you want to avoid passing `void*` | 31 * `cx_hash_key_bytes()` is strongly typed if you want to avoid passing `void*` |
| 31 * `cx_hash_key_str()` conveniently takes a C string and computes the length | 32 * `cx_hash_key_str()` conveniently takes a C string and computes the length |
| 33 * `cx_hash_key_ustr()` same as before, but for `unsigned char*` | |
| 32 * `cx_hash_key_cxstr()` conveniently takes a [UCX string](string.h.md) | 34 * `cx_hash_key_cxstr()` conveniently takes a [UCX string](string.h.md) |
| 33 | 35 |
| 34 In all cases, the hash will be available in the `hash` field of the returned structure. | 36 In all cases, the hash will be available in the `hash` field of the returned structure. |
| 35 | 37 |
| 38 > Usually you will never need to call any of the other functions directly. | |
| 39 > You can always create a `CxHashKey` structure by using the `CX_HASH_KEY()` macro | |
| 40 > (when the length of the key is implicitly clear) or by using the `cx_hash_key()` function. | |
| 41 > {style="note"} | |
| 42 | |
| 36 > UCX assigns the hash value `1574210520` to the `NULL` pointer. | 43 > UCX assigns the hash value `1574210520` to the `NULL` pointer. |
| 37 > This is a careful choice which is not standard MurmurHash2 and an extension to support `NULL` pointers. | 44 > This is a careful choice which is not standard MurmurHash2 and an extension to support `NULL` pointers. |
| 45 | |
| 46 Hashes from integers are created more efficiently by mixing up the bits to produce a good statistical distribution. | |
| 47 The function `cx_hash_u32()` and `cx_hash_u64()` are provided for this purpose and provide collision-free hashes. | |
| 48 The corresponding functions `cx_hash_key_u32()` and `cx_hash_key_u64()` can be used to create `CxHashKey` structures with those hashes. | |
| 49 | |
| 50 > Since integer hashes are collision-free, there is no need to store any `data` in the `CxHashKey` structure. | |
| 38 | 51 |
| 39 If you want to create a hash completely manually, | 52 If you want to create a hash completely manually, |
| 40 you can initialize the `data` and `len` members of `CxHashKey` | 53 you can initialize the `data` and `len` members of `CxHashKey` |
| 41 and call `cx_hash_murmur()`. | 54 and call `cx_hash_murmur()`. |
| 42 It is _not_ recommended to do so. | 55 It is _not_ recommended to do so. |
| 47 key.data = mystring; | 60 key.data = mystring; |
| 48 key.len = strlen(mystring); | 61 key.len = strlen(mystring); |
| 49 cx_hash_murmur(&key); | 62 cx_hash_murmur(&key); |
| 50 ``` | 63 ``` |
| 51 | 64 |
| 52 Hashes from integers are created more efficiently by mixing up the bits to produce a good statistical distribution. | |
| 53 The function `cx_hash_u32()` and `cx_hash_u64()` are provided for this purpose and provide collision-free hashes. | |
| 54 The corresponding functions `cx_hash_key_u32()` and `cx_hash_key_u64()` can be used to create `CxHashKey` structures with those hashes. | |
| 55 | |
| 56 > Since integer hashes are collision-free, there is no need to store any `data` in the `CxHashKey` structure. | |
| 57 | |
| 58 Hash keys are compared with `cx_hash_key_cmp()`. | 65 Hash keys are compared with `cx_hash_key_cmp()`. |
| 59 | 66 |
| 60 <seealso> | 67 <seealso> |
| 61 <category ref="apidoc"> | 68 <category ref="apidoc"> |
| 62 <a href="https://ucx.sourceforge.io/api/hash__key_8h.html">hash_key.h</a> | 69 <a href="https://ucx.sourceforge.io/api/hash__key_8h.html">hash_key.h</a> |
