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rax.h
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rax.h
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#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, void **old);
int raxRemove(rax *rax, unsigned char *s, size_t len, void **old);
void *raxFind(rax *rax, unsigned char *s, size_t len);
void raxFree(rax *rax);
void raxStart(raxIterator *it, rax *rt);
int raxSeek(raxIterator *it, const char *op, unsigned char *ele, size_t len);
int raxNext(raxIterator *it);
int raxPrev(raxIterator *it);
int raxRandomWalk(raxIterator *it, size_t steps);
int raxCompare(raxIterator *iter, const char *op, unsigned char *key, size_t key_len);
void raxStop(raxIterator *it);
void raxShow(rax *rax);
#endif