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Diffstat (limited to 'src/mesa/main/hash.h')
-rw-r--r-- | src/mesa/main/hash.h | 56 |
1 files changed, 56 insertions, 0 deletions
diff --git a/src/mesa/main/hash.h b/src/mesa/main/hash.h index b44959eb13e..02960e3b356 100644 --- a/src/mesa/main/hash.h +++ b/src/mesa/main/hash.h @@ -35,6 +35,62 @@ #include "glheader.h" #include "imports.h" +/** + * Magic GLuint object name that gets stored outside of the struct hash_table. + * + * The hash table needs a particular pointer to be the marker for a key that + * was deleted from the table, along with NULL for the "never allocated in the + * table" marker. Legacy GL allows any GLuint to be used as a GL object name, + * and we use a 1:1 mapping from GLuints to key pointers, so we need to be + * able to track a GLuint that happens to match the deleted key outside of + * struct hash_table. We tell the hash table to use "1" as the deleted key + * value, so that we test the deleted-key-in-the-table path as best we can. + */ +#define DELETED_KEY_VALUE 1 + +/** @{ + * Mapping from our use of GLuint as both the key and the hash value to the + * hash_table.h API + * + * There exist many integer hash functions, designed to avoid collisions when + * the integers are spread across key space with some patterns. In GL, the + * pattern (in the case of glGen*()ed object IDs) is that the keys are unique + * contiguous integers starting from 1. Because of that, we just use the key + * as the hash value, to minimize the cost of the hash function. If objects + * are never deleted, we will never see a collision in the table, because the + * table resizes itself when it approaches full, and thus key % table_size == + * key. + * + * The case where we could have collisions for genned objects would be + * something like: glGenBuffers(&a, 100); glDeleteBuffers(&a + 50, 50); + * glGenBuffers(&b, 100), because objects 1-50 and 101-200 are allocated at + * the end of that sequence, instead of 1-150. So far it doesn't appear to be + * a problem. + */ +static inline bool +uint_key_compare(const void *a, const void *b) +{ + return a == b; +} + +static inline uint32_t +uint_hash(GLuint id) +{ + return id; +} + +static inline uint32_t +uint_key_hash(const void *key) +{ + return uint_hash((uintptr_t)key); +} + +static inline void * +uint_key(GLuint id) +{ + return (void *)(uintptr_t) id; +} +/** @} */ /** * The hash table data structure. |