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Diffstat (limited to 'src/rax.h')
| -rw-r--r-- | src/rax.h | 158 |
1 files changed, 158 insertions, 0 deletions
diff --git a/src/rax.h b/src/rax.h new file mode 100644 index 000000000..76330e0de --- /dev/null +++ b/src/rax.h @@ -0,0 +1,158 @@ +#ifndef RAX_H +#define RAX_H + +#include <stdint.h> + +/* Representation of a radix tree as implemented in this file, that contains + * the strings "foo", "foobar" and "footer" after the insertion of each + * word. When the node represents a key inside the radix tree, we write it + * between [], otherwise it is written between (). + * + * This is the vanilla representation: + * + * (f) "" + * \ + * (o) "f" + * \ + * (o) "fo" + * \ + * [t b] "foo" + * / \ + * "foot" (e) (a) "foob" + * / \ + * "foote" (r) (r) "fooba" + * / \ + * "footer" [] [] "foobar" + * + * However, this implementation implements a very common optimization where + * successive nodes having a single child are "compressed" into the node + * itself as a string of characters, each representing a next-level child, + * and only the link to the node representing the last character node is + * provided inside the representation. So the above representation is turend + * into: + * + * ["foo"] "" + * | + * [t b] "foo" + * / \ + * "foot" ("er") ("ar") "foob" + * / \ + * "footer" [] [] "foobar" + * + * However this optimization makes the implementation a bit more complex. + * For instance if a key "first" is added in the above radix tree, a + * "node splitting" operation is needed, since the "foo" prefix is no longer + * composed of nodes having a single child one after the other. This is the + * above tree and the resulting node splitting after this event happens: + * + * + * (f) "" + * / + * (i o) "f" + * / \ + * "firs" ("rst") (o) "fo" + * / \ + * "first" [] [t b] "foo" + * / \ + * "foot" ("er") ("ar") "foob" + * / \ + * "footer" [] [] "foobar" + * + * Similarly after deletion, if a new chain of nodes having a single child + * is created (the chain must also not include nodes that represent keys), + * it must be compressed back into a single node. + * + */ + +#define RAX_NODE_MAX_SIZE ((1<<29)-1) +typedef struct raxNode { + uint32_t iskey:1; /* Does this node contain a key? */ + uint32_t isnull:1; /* Associated value is NULL (don't store it). */ + uint32_t iscompr:1; /* Node is compressed. */ + uint32_t size:29; /* Number of children, or compressed string len. */ + /* Data layout is as follows: + * + * If node is not compressed we have 'size' bytes, one for each children + * character, and 'size' raxNode pointers, point to each child node. + * Note how the character is not stored in the children but in the + * edge of the parents: + * + * [header strlen=0][abc][a-ptr][b-ptr][c-ptr](value-ptr?) + * + * if node is compressed (strlen != 0) the node has 1 children. + * In that case the 'size' bytes of the string stored immediately at + * the start of the data section, represent a sequence of successive + * nodes linked one after the other, for which only the last one in + * the sequence is actually represented as a node, and pointed to by + * the current compressed node. + * + * [header strlen=3][xyz][z-ptr](value-ptr?) + * + * Both compressed and not compressed nodes can represent a key + * with associated data in the radix tree at any level (not just terminal + * nodes). + * + * If the node has an associated key (iskey=1) and is not NULL + * (isnull=0), then after the raxNode pointers poiting to the + * childen, an additional value pointer is present (as you can see + * in the representation above as "value-ptr" field). + */ + unsigned char data[]; +} raxNode; + +typedef struct rax { + raxNode *head; + uint64_t numele; + uint64_t numnodes; +} rax; + +/* Stack data structure used by raxLowWalk() in order to, optionally, return + * a list of parent nodes to the caller. The nodes do not have a "parent" + * field for space concerns, so we use the auxiliary stack when needed. */ +#define RAX_STACK_STATIC_ITEMS 32 +typedef struct raxStack { + void **stack; /* Points to static_items or an heap allocated array. */ + size_t items, maxitems; /* Number of items contained and total space. */ + /* Up to RAXSTACK_STACK_ITEMS items we avoid to allocate on the heap + * and use this static array of pointers instead. */ + void *static_items[RAX_STACK_STATIC_ITEMS]; + int oom; /* True if pushing into this stack failed for OOM at some point. */ +} raxStack; + +/* Radix tree iterator state is encapsulated into this data structure. */ +#define RAX_ITER_STATIC_LEN 128 +#define RAX_ITER_JUST_SEEKED (1<<0) /* Iterator was just seeked. Return current + element for the first iteration and + clear the flag. */ +#define RAX_ITER_EOF (1<<1) /* End of iteration reached. */ +#define RAX_ITER_SAFE (1<<2) /* Safe iterator, allows operations while + iterating. But it is slower. */ +typedef struct raxIterator { + int flags; + rax *rt; /* Radix tree we are iterating. */ + unsigned char *key; /* The current string. */ + void *data; /* Data associated to this key. */ + size_t key_len; /* Current key length. */ + size_t key_max; /* Max key len the current key buffer can hold. */ + unsigned char key_static_string[RAX_ITER_STATIC_LEN]; + raxNode *node; /* Current node. Only for unsafe iteration. */ + raxStack stack; /* Stack used for unsafe iteration. */ +} raxIterator; + +/* A special pointer returned for not found items. */ +extern void *raxNotFound; + +/* Exported API. */ +rax *raxNew(void); +int raxInsert(rax *rax, unsigned char *s, size_t len, void *data); +int raxRemove(rax *rax, unsigned char *s, size_t len); +void *raxFind(rax *rax, unsigned char *s, size_t len); +void raxFree(rax *rax); +void raxStart(raxIterator *it, rax *rt); +int raxSeek(raxIterator *it, unsigned char *ele, size_t len, const char *op); +int raxNext(raxIterator *it, unsigned char *stop, size_t stoplen, char *op); +int raxPrev(raxIterator *it, unsigned char *stop, size_t stoplen, char *op); +void raxStop(raxIterator *it); +void raxShow(rax *rax); + +#endif |