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foundationdb/fdbserver/art_impl.h

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/*
* art_impl.h
*
* This source file is part of the FoundationDB open source project
*
* Copyright 2013-2020 Apple Inc. and the FoundationDB project authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef ART_IMPL_H
#define ART_IMPL_H
using art_tree = VersionedBTree::art_tree;
using art_leaf = art_tree::art_leaf;
#define art_node art_tree::art_node
int art_tree::fat_leaf_offset[] = {
0, 0, 0, 0, 0,
sizeof(art_node4), sizeof(art_node16), sizeof(art_node48), sizeof(art_node256)};
int art_tree::node_sizes[] = {
0,
sizeof(art_node4), sizeof(art_node16), sizeof(art_node48), sizeof(art_node256),
sizeof(art_node4_kv), sizeof(art_node16_kv), sizeof(art_node48_kv), sizeof(art_node256_kv)};
VersionedBTree::art_iterator art_tree::insert(KeyRef &k, void *value) {
#define INIT_DEPTH 0
#define REPLACE 1
int old_val = 0;
art_leaf *l = iterative_insert(this->root, &this->root, k, value, INIT_DEPTH, &old_val, REPLACE);
if (!old_val) this->size++;
return VersionedBTree::art_iterator(l);
}
VersionedBTree::art_iterator art_tree::insert_if_absent(KeyRef &k, void *value, int *existing) {
#define INIT_DEPTH 0
#define DONTREPLACE 0
art_leaf *l = iterative_insert(this->root, &this->root, k, value, INIT_DEPTH, existing, DONTREPLACE);
if (!existing) this->size++;
return VersionedBTree::art_iterator(l);
}
VersionedBTree::art_iterator art_tree::lower_bound(const KeyRef &key) {
if (!size) return art_iterator(nullptr);
art_node *n = root;
art_leaf *res = nullptr;
int depth = 0;
art_bound_iterative(n, key, depth, &res, false);
return art_iterator(res);
}
VersionedBTree::art_iterator art_tree::upper_bound(const KeyRef &key) {
if (!size) return art_iterator(nullptr);
art_node *n = root;
art_leaf *res = nullptr;
int depth = 0;
art_bound_iterative(n, key, depth, &res, true);
return art_iterator(res);
}
struct stack_entry {
art_node *node;
unsigned char key;
stack_entry *prev;
stack_entry(art_node *n, unsigned char k, stack_entry *s) : node(n), key(k), prev(s) {
}
stack_entry() {
}
};
art_leaf *art_tree::minimum(art_node *n) {
// Handle base cases
if (!n) {
return NULL;
}
if (ART_IS_LEAF(n)) {
return ART_LEAF_RAW(n);
}
int idx;
switch (n->type) {
case ART_NODE4:
return minimum(((art_node4 *) n)->children[0]);
case ART_NODE16:
return minimum(((art_node16 *) n)->children[0]);
case ART_NODE48:
idx = 0;
while (!((art_node48 *) n)->keys[idx]) idx++;
idx = ((art_node48 *) n)->keys[idx] - 1;
return minimum(((art_node48 *) n)->children[idx]);
case ART_NODE256:
idx = 0;
while (!((art_node256 *) n)->children[idx]) idx++;
return minimum(((art_node256 *) n)->children[idx]);
case ART_NODE256_KV:
case ART_NODE48_KV:
case ART_NODE16_KV:
case ART_NODE4_KV:
return ART_FAT_NODE_LEAF(n);
default:
printf("%d\n", n->type);
UNSTOPPABLE_ASSERT(false);
}
}
art_leaf *art_tree::maximum(art_node *n) {
// Handle base cases
if (!n) return NULL;
if (ART_IS_LEAF(n)) return ART_LEAF_RAW(n);
int idx;
switch (n->type) {
case ART_NODE4:
case ART_NODE4_KV:
return maximum(((art_node4 *) n)->children[n->num_children - 1]);
case ART_NODE16:
case ART_NODE16_KV:
return maximum(((art_node16 *) n)->children[n->num_children - 1]);
case ART_NODE48:
case ART_NODE48_KV:
idx = 255;
while (!((art_node48 *) n)->keys[idx]) idx--;
idx = ((art_node48 *) n)->keys[idx] - 1;
return maximum(((art_node48 *) n)->children[idx]);
case ART_NODE256:
case ART_NODE256_KV:
idx = 255;
while (!((art_node256 *) n)->children[idx]) idx--;
return maximum(((art_node256 *) n)->children[idx]);
default:
UNSTOPPABLE_ASSERT(false);
}
}
void art_tree::art_bound_iterative(art_node *n, const KeyRef &k, int depth, art_leaf **result, bool strict) {
static stack_entry arena[ART_MAX_KEY_LEN]; //Single threaded implementation.
stack_entry *head = nullptr, *tmp, *curr_arena = arena;
int ret;
art_node **child;
unsigned char *key = (unsigned char *) k.begin();
while (n) {
ret = check_bound_node(n, k, &depth, result, strict);
if (ret == ART_I_FOUND) {
return;
}
if (ret == ART_I_BACKTRACK) break;
if (ret == ART_I_DEPTH) {
head = new(curr_arena++) stack_entry(n, key[depth], head);
//if the child is NULL, then we have to look right; i.e., we start backtracking
child = find_child(n, key[depth]);
if (!child)break;
n = *child;
depth = depth + 1;
//else go on
} else {
UNSTOPPABLE_ASSERT(false);
}
}
art_node *next;
while (head) {
n = head->node;
find_next(n, head->key, &next);
if (next) {
*result = minimum(next);
break;
} else {
tmp = head;
head = head->prev;
}
}
}
int art_tree::check_bound_node(art_node *n, const KeyRef &k, int *depth_p, art_leaf **result, bool strict) {
if (ART_IS_LEAF(n)) {
int ret = art_bound_leaf(n, k, *depth_p, result);
*result = ART_LEAF_RAW(n);
if (ret == ART_LEAF_SMALLER_KEY || (ret == ART_LEAF_MATCH_KEY && strict)) {
*result = (*result)->next;
}
return ART_I_FOUND;
}
int depth = *depth_p;
const int key_len = k.size();
if (n->type < ART_NODE4_KV) {
const uint32_t n_partial_len = n->partial_len;
//Case 1: the search ends on this node
if (key_len <= (depth + n_partial_len)) {
//Easy case w/o checking prefix:
if (0 == n_partial_len) {
*result = minimum(n);
return ART_I_FOUND;
} else {
//The Whole prefix is the set of bytes after the first depth bytes and up to partial_len
art_leaf *min_leaf;
int prefix_differs = signed_prefix_mismatch(n, k, depth, &min_leaf, true);
if (prefix_differs < 0) {//our key is greater than or equal to the partial prefix. I.e., this subtree
//only stores smaller keys.
return ART_I_BACKTRACK;
} else {//our key is less than or equal to the partial prefix. So this subtree stores our bound (modulo null leaf)
if (min_leaf == (art_leaf *) ART_MIN_LEAF_UNSET) {
min_leaf = minimum(n);
}
*result = min_leaf;
return ART_I_FOUND;
}
}
}
//Case 2: the search has to go deeper
//First, look if you have any prefix. If you do, you have to check this prefix before checking your children
if (n_partial_len) {
art_leaf *min_leaf;
int prefix_differs = signed_prefix_mismatch(n, k, depth, &min_leaf, true);
if (prefix_differs == 0) {
//The partial prefix matches (0 ==> match)
//The mismatch happens after the prefix covered by the node, so it is fine to check its children
*depth_p += n->partial_len;
return ART_I_DEPTH;
} else {
//The mismatch happens in the prefix of this node. Now there are two options
//1. The subtree stores smaller keys. Have to backtrack
if (prefix_differs < 0) {
return ART_I_BACKTRACK;
} else {
if (min_leaf == (art_leaf *) ART_MIN_LEAF_UNSET) {
min_leaf = minimum(n);
}
*result = min_leaf;
return ART_I_FOUND;
}
}
}
return ART_I_DEPTH;
} else {
if (key_len <= depth + n->partial_len) {//Case 1: the key ends here
art_leaf *l = ART_FAT_NODE_LEAF(n);
// Check if the expanded path matches
int m = leaf_matches_signed(l, k, depth);
if (!m) {
// We have a match. If the bound is not strict, we save the result
if (!strict) {
*result = l;
return ART_I_FOUND;
} else {//Assuming --as we do-- that we have a child, the smallest child in the subtree is the bound
*result = minimum_kv(n);
return ART_I_FOUND; //We have found the bound. We use this return value so that the value
//We set as result is propagated directly
}
}
if (m < 0) {
// The key in the fat node is smaller than the desired key
// This means that the target key does not exist.
// Also, it means that this subtree as a whole is smaller than the target key
// So the bound has to be searched by my daddy
return ART_I_BACKTRACK;
} else {
*result = l;
return ART_I_FOUND;
}
}
if (n->partial_len) {
art_leaf *l = ART_FAT_NODE_LEAF(n);
//Note we know target key *does not* end here, so we just need to check the prefix
//To avoid distinguishing whether the prefix is larger or smaller than min, we compare with the leaf
//That is readily available w/o issuing a "min"
//The fat leaf key includes the prefix for sure
int cmp = memcmp(((unsigned char *) k.begin()) + depth, ((unsigned char *) l->key.begin()) + depth, n->partial_len);
if (cmp < 0) {//Target key is smaller, fat key is then the smallest key larger than current key
*result = l;
return ART_I_FOUND;
} else if (cmp > 0) {//Target key is larger than key and hence than subtree. Ask daddy to go right
return ART_I_BACKTRACK;
}
//If prefix is the same, then go in depth with the updated depth value
*depth_p += n->partial_len;
return ART_I_DEPTH;
}
return ART_I_DEPTH;
}
}
int art_tree::art_bound_leaf(art_node *n, const KeyRef &k, int depth, art_leaf **result) {
n = (art_node *) ART_LEAF_RAW(n);
// Check if the expanded path matches
int m = leaf_matches_signed((art_leaf *) n, k, depth);
if (0 == m) return ART_LEAF_MATCH_KEY;
if (m < 0) return ART_LEAF_SMALLER_KEY;
return ART_LEAF_LARGER_KEY;
}
int art_tree::leaf_matches_signed(art_leaf *n, const KeyRef &k, int depth) {
const int key_len = k.size();
const unsigned char *key = k.begin();
int common_length = min(n->key.size() - depth, key_len - depth);
// Compare the keys starting at the depth
int cmp = memcmp((n->key.begin()) + depth, key + depth, common_length);
if (cmp)return cmp;
return n->key.size() - key_len;
}
int art_tree::leaf_matches(const art_leaf *n, const KeyRef &k, int depth) {
const int key_len = k.size();
// Fail if the key lengths are different
if (n->key.size() != (uint32_t) key_len) return 1;
const unsigned char *key = k.begin();
// Compare the keys starting at the depth
return memcmp(((unsigned char *) (n->key).begin()) + depth, key + depth, key_len - depth);
}
int art_tree::signed_prefix_mismatch(art_node *n, const KeyRef &k, int depth, art_leaf **min_leaf, bool find_min) {
int all_to_check = min(n->partial_len, k.size() - depth);
int max_cmp = min(ART_MAX_PREFIX_LEN, all_to_check);
//Mark the leaf as unset right away, so that if you don't return in the first loop AND you don't enter the
//Second loop, the leaf is marked correctly as unset
*min_leaf = (art_leaf *) ART_MIN_LEAF_UNSET;
int idx;
for (idx = 0; idx < max_cmp; idx++) {
if (n->partial[idx] != k.begin()[depth + idx]) {
return ((int) n->partial[idx]) - ((int) (k.begin()[depth + idx]));
}
}
//So far they are the same.
//There are two cases now. They are the same BUT we have to check after ART_MAX_PREFIX_LEN, or they are the same
//and there's nothing more to check.
if (all_to_check <= ART_MAX_PREFIX_LEN)return 0;
//Else, we need to go deeper and check the bytes after ART_MAX_PREFIX_LEN
int remaining = all_to_check - ART_MAX_PREFIX_LEN;
// If the prefix is short we can avoid finding a leaf
if (remaining > 0) {
// Prefix is longer than what we've checked, find a leaf
art_leaf *l = find_min ? minimum(n) : maximum(n);
*min_leaf = l;
//We have to compare the last partial_len - ART_MAX_PREFIX_LEN bytes
//If the minimum is below me, then it has at least my same prefix, so I can safely check
//all its bytes from depth to depth+remaining
for (; idx < ART_MAX_PREFIX_LEN + remaining; idx++) {
if (l->key.begin()[idx + depth] != k.begin()[depth + idx]) {
return ((int) l->key.begin()[idx + depth]) - ((int) k.begin()[depth + idx]);
}
}
}
return 0;
}
art_leaf *art_tree::minimum_kv(art_node *n) {
// Handle base cases
if (!n) {
return NULL;
}
if (ART_IS_LEAF(n)) {
return ART_LEAF_RAW(n);
}
int idx;
switch (n->type) {
case ART_NODE4_KV:
return minimum(((art_node4 *) n)->children[0]);
case ART_NODE16_KV:
return minimum(((art_node16 *) n)->children[0]);
case ART_NODE48_KV:
idx = 0;
while (!((art_node48 *) n)->keys[idx]) idx++;
idx = ((art_node48 *) n)->keys[idx] - 1;
return minimum(((art_node48 *) n)->children[idx]);
case ART_NODE256_KV:
idx = 0;
while (!((art_node256 *) n)->children[idx]) idx++;
return minimum(((art_node256 *) n)->children[idx]);
default:
UNSTOPPABLE_ASSERT(false);
}
}
art_node **art_tree::find_child(art_node *n, unsigned char c) {
int i, mask, bitfield;
union {
art_node4 *p1;
art_node16 *p2;
art_node48 *p3;
art_node256 *p4;
} p;
switch (n->type) {
case ART_NODE4:
case ART_NODE4_KV:
p.p1 = (art_node4 *) n;
switch (n->num_children) {
case 4:
if (p.p1->keys[3] == c) { return &p.p1->children[3]; }
case 3:
if (p.p1->keys[2] == c) { return &p.p1->children[2]; }
case 2:
if (p.p1->keys[1] == c) { return &p.p1->children[1]; }
/*
* We need a case 1. Otherwise this could happen: we could be looking for char '0'
* On a node with 0 children (root node). Since the node has been zeroed on allocation,
* we get that key[0] is exactly '0', and we think we have found a child. Duh.
*/
case 1:
if (p.p1->keys[0] == c) { return &p.p1->children[0]; }
default:
break;
}
break;
{
case ART_NODE16:
case ART_NODE16_KV:
__m128i cmp;
p.p2 = (art_node16 *) n;
// Compare the key to all 16 stored keys
cmp = _mm_cmpeq_epi8(_mm_set1_epi8(c),
_mm_loadu_si128((__m128i *) p.p2->keys));
// Use a mask to ignore children that don't exist
mask = (1 << n->num_children) - 1;
bitfield = _mm_movemask_epi8(cmp) & mask;
/*
* If we have a match (any bit set) then we can
* return the pointer match using ctz to get
* the index.
*/
if (bitfield)
return &p.p2->children[ctz(bitfield)];
break;
}
case ART_NODE48:
case ART_NODE48_KV:
p.p3 = (art_node48 *) n;
i = p.p3->keys[c];
if (i)
return &p.p3->children[i - 1];
break;
case ART_NODE256:
case ART_NODE256_KV:
p.p4 = (art_node256 *) n;
if (p.p4->children[c])
return &p.p4->children[c];
break;
default:
UNSTOPPABLE_ASSERT(false);
}
return NULL;
}
void art_tree::find_next(art_node *n, unsigned char c, art_node **out) {
int i, mask, bitfield;
union {
art_node4 *p1;
art_node16 *p2;
art_node48 *p3;
art_node256 *p4;
} p;
*out = nullptr;
switch (n->type) {
case ART_NODE4:
case ART_NODE4_KV:
p.p1 = (art_node4 *) n;
switch (n->num_children) {//unrolling loop
case 4:
if (p.p1->keys[0] > c) {
*out = p.p1->children[0];
break;
}
if (p.p1->keys[1] > c) {
*out = p.p1->children[1];
break;
}
if (p.p1->keys[2] > c) {
*out = p.p1->children[2];
break;
}
if (p.p1->keys[3] > c) {
*out = p.p1->children[3];
break;
}
break;
case 3:
if (p.p1->keys[0] > c) {
*out = p.p1->children[0];
break;
}
if (p.p1->keys[1] > c) {
*out = p.p1->children[1];
break;
}
if (p.p1->keys[2] > c) {
*out = p.p1->children[2];
break;
}
break;
case 2:
if (p.p1->keys[0] > c) {
*out = p.p1->children[0];
break;
}
if (p.p1->keys[1] > c) {
*out = p.p1->children[1];
break;
}
break;
//We add a case 1 just in case... (see previous similar comment)
case 1:
if (p.p1->keys[0] > c) {
*out = p.p1->children[0];
break;
}
default:
break;
}
break;
{
case ART_NODE16:
case ART_NODE16_KV:
__m128i cmp;
p.p2 = (art_node16 *) n;
//We did not find the child corresponding to the key. Let's see if we have a next at least
// Compare the key to all 16 stored keys for Greater than
cmp = _mm_cmplt_epu8(_mm_set1_epi8(c), _mm_loadu_si128((__m128i *) p.p2->keys));
// Use a mask to ignore children that don't exist
mask = (1 << n->num_children) - 1;
bitfield = _mm_movemask_epi8(cmp) & mask;
if (bitfield) {
//ALL children greater than char have their bit set
//We need the smallest one
//let's get the least significant bit that is set in the bitfield
int one = ctz(bitfield);
*out = p.p2->children[one];
}
break;
}
case ART_NODE48:
case ART_NODE48_KV: {
p.p3 = (art_node48 *) n;
if (c == 255)break;
unsigned char cc = c + 1;
do {
i = p.p3->keys[cc];
if (i) {
*out = p.p3->children[i - 1];
break;
}
++cc;
} while (cc > 0); //cc wraps around at 256
break;
}
case ART_NODE256:
case ART_NODE256_KV: {
p.p4 = (art_node256 *) n;
unsigned char cc = c + 1;
if (c == 255)break;
do {
if (p.p4->children[cc]) {
*out = p.p4->children[cc];
break;
}
++cc;
} while (cc > 0); //cc wraps around at 256
break;
}
default:
UNSTOPPABLE_ASSERT(false);
}
}
void art_tree::recursive_delete_binary(art_node *n, art_node **ref, const KeyRef &k, int depth) {
// Bail if the prefix does not match
unsigned char *key = (unsigned char *) k.begin();
unsigned int key_len = (unsigned int) k.size();
if (n->partial_len) {
int prefix_len = check_prefix(n, k, depth);
if (prefix_len != min(ART_MAX_PREFIX_LEN, n->partial_len)) {
return;
}
depth = depth + n->partial_len;
}
// Find child node
art_node **child = find_child(n, key[depth]);
if (!child) return;
//The child contains the key to be deleted in two cases
//1. The child is a leaf (and the key matches)
//2. THe child is a fat node (and the key ands in the node and the key matches)
// If the child is leaf, delete from this node
if (ART_IS_LEAF(*child)) {
art_leaf *l = ART_LEAF_RAW(*child);
if (!leaf_matches(l, k, depth)) {
remove_child(n, ref, key[depth], child, depth);
if (l->prev) {
l->prev->next = l->next;
}
if (l->next) {
l->next->prev = l->prev;
}
return;
}
return;
} else {
// Fat node and key ends within the child
// Note that the predicate is on the child node, so at depth+1
if ((*child)->type >= ART_NODE4_KV && (key_len == depth + 1 + (*child)->partial_len)) {
//Check if key matches
art_leaf *l = ART_FAT_NODE_LEAF((*child));
//Return NULL if key does not match
if (leaf_matches(l, k, depth + 1)) {
return;
}
//Set prev and next, since the leaf is going away
if (l->prev) {
l->prev->next = l->next;
}
if (l->next) {
l->next->prev = l->prev;
}
//Remove the fat child. This also triggers compaction
//NOTE: we are removing the fat leaf on our child, which is at depth+1!!!
remove_fat_child(*child, child, depth + 1);
return;
}
// Recurse if key is not supposed to be in the child. The child is going to be an internal node
recursive_delete_binary(*child, child, k, depth + 1);
}
}
int art_tree::check_prefix(const art_node *n, const KeyRef &k, int depth) {
int max_cmp = min(min(n->partial_len, ART_MAX_PREFIX_LEN), k.size() - depth);
int idx;
for (idx = 0; idx < max_cmp; idx++) {
if (n->partial[idx] != ((unsigned char *) k.begin())[depth + idx])
return idx;
}
return idx;
}
//Remove a LEAF from a node256/node256kv
void art_tree::remove_child256(art_node256 *n, art_node **ref, unsigned char c) {
n->children[c] = NULL;
n->n.num_children--;
// Resize to a node48 on underflow, not immediately to prevent
// trashing if we sit on the 48/49 boundary
if (n->n.num_children == 37) {
art_node48 *new_node;
if (n->n.type == ART_NODE256_KV) {
new_node = (art_node48 *) alloc_node(ART_NODE48_KV);
ART_FAT_NODE_LEAF(&new_node->n) = ART_FAT_NODE_LEAF(&n->n);
} else {
new_node = (art_node48 *) alloc_node(ART_NODE48);
}
*ref = (art_node *) new_node;
copy_header((art_node *) new_node, (art_node *) n);
int pos = 0;
for (int i = 0; i < 256; i++) {
if (n->children[i]) {
new_node->children[pos] = n->children[i];
new_node->keys[i] = pos + 1;
pos++;
}
}
}
}
void art_tree::remove_fat_child256(art_node256_kv *n, art_node **ref) {
//Delete the child by turning the fat node to a normal internal node
n->n.n.type = ART_NODE256;
*ref = (art_node *) n;
}
//Remove a LEAF from a node48/node48kv
void art_tree::remove_child48(art_node48 *n, art_node **ref, unsigned char c) {
int pos = n->keys[c];
n->keys[c] = 0;
n->children[pos - 1] = NULL;
n->n.num_children--;
if (n->n.num_children == 12) {
art_node16 *new_node;
if (n->n.type == ART_NODE48_KV) {
new_node = (art_node16 *) alloc_node(ART_NODE16_KV);
ART_FAT_NODE_LEAF(&new_node->n) = ART_FAT_NODE_LEAF(&n->n);
} else {
new_node = (art_node16 *) alloc_node(ART_NODE16);
}
*ref = (art_node *) new_node;
copy_header((art_node *) new_node, (art_node *) n);
int child = 0;
for (int i = 0; i < 256; i++) {
pos = n->keys[i];
if (pos) {
new_node->keys[child] = i;
new_node->children[child] = n->children[pos - 1];
child++;
}
}
}
}
void art_tree::remove_fat_child48(art_node48_kv *n, art_node **ref) {
//Delete the child by turning the fat node to a normal internal node
n->n.n.type = ART_NODE48;
*ref = (art_node *) n;
}
//Remove a LEAF from a node16/node16kv
void art_tree::remove_child16(art_node16 *n, art_node **ref, art_node **l) {
int pos = l - n->children;
memmove(n->keys + pos, n->keys + pos + 1, n->n.num_children - 1 - pos);
memmove(n->children + pos, n->children + pos + 1, (n->n.num_children - 1 - pos) * sizeof(void *));
n->n.num_children--;
if (n->n.num_children == 3) {
art_node4 *new_node;
if (n->n.type == ART_NODE16_KV) {
new_node = (art_node4 *) alloc_node(ART_NODE4_KV);
ART_FAT_NODE_LEAF(&new_node->n) = ART_FAT_NODE_LEAF(&n->n);
} else {
new_node = (art_node4 *) alloc_node(ART_NODE4);
}
*ref = (art_node *) new_node;
copy_header((art_node *) new_node, (art_node *) n);
memcpy(new_node->keys, n->keys, 4);
memcpy(new_node->children, n->children, 4 * sizeof(void *));
}
}
void art_tree::remove_fat_child16(art_node16_kv *n, art_node **ref) {
//Delete the child by turning the fat node to a normal internal node
n->n.n.type = ART_NODE16;
*ref = (art_node *) n;
}
//Remove a LEAF from a node4/node4kv
void art_tree::remove_child4(art_node4 *n, art_node **ref, art_node **l, int depth) {
int pos = l - n->children;
//We should do this only if then we do not remove the node altogether
memmove(n->keys + pos, n->keys + pos + 1, n->n.num_children - 1 - pos);
memmove(n->children + pos, n->children + pos + 1, (n->n.num_children - 1 - pos) * sizeof(void *));
n->n.num_children--;
// Remove nodes with only a single child
//This can only be done if the node is not a fat node.
//In that case, the key in the fat node is a prefix to the key in the only child
//And hence has to be preserved in the fat node
if (n->n.num_children == 1 && (n->n.type < ART_NODE4_KV) && depth) {
art_node *child = n->children[0];
if (!ART_IS_LEAF(child)) {
// Concatenate the prefixes
int prefix = n->n.partial_len;
if (prefix < ART_MAX_PREFIX_LEN) {
n->n.partial[prefix] = n->keys[0];
prefix++;
}
if (prefix < ART_MAX_PREFIX_LEN) {
int sub_prefix = min(child->partial_len, ART_MAX_PREFIX_LEN - prefix);
memcpy(n->n.partial + prefix, child->partial, sub_prefix);
prefix += sub_prefix;
}
// Store the prefix in the child
memcpy(child->partial, n->n.partial, min(prefix, ART_MAX_PREFIX_LEN));
child->partial_len += n->n.partial_len + 1;
}
//This is done also for the leaf. If the only son is a leaf, just delete the internal node
//And have the father of the deleted internal node point directly to the leaf.
*ref = child;
}
//What can happen now is that the node has ZERO children.
//If you have a fat node, you cannot compress when you get to one child
//So it can happen that the one child get removed
//At that point, you transform the fat node into a leaf: the fat key is not prefix of any subtree!
//This should only happen to a node4kv: if the node is normal, then already when there there is 1 child
//the node gets compressed.
//We still check for depth b/c we want to avoid that root becomes empty and becomes a leaf
else if (n->n.num_children == 0 && depth) {
*ref = (art_node *) SET_LEAF((art_node *) ART_FAT_NODE_LEAF(&n->n));
} else if (!depth && n->n.num_children == 0) {
n->children[0] = nullptr;
}
}
void art_tree::remove_fat_child4(art_node4_kv *n, art_node **ref, int depth) {
//Delete the child by turning the fat node to a normal internal node
n->n.n.type = ART_NODE4;
*ref = (art_node *) n; //Tell daddy that my address has changed
art_node4 *node = (art_node4 *) n;
// Remove nodes with only a single child
if (node->n.num_children == 1 && depth) {
art_node *child = node->children[0];
if (!ART_IS_LEAF(child)) {
// Concatenate the prefixes
int prefix = node->n.partial_len;
if (prefix < ART_MAX_PREFIX_LEN) {
node->n.partial[prefix] = node->keys[0];
prefix++;
}
if (prefix < ART_MAX_PREFIX_LEN) {
int sub_prefix = min(child->partial_len, ART_MAX_PREFIX_LEN - prefix);
memcpy(node->n.partial + prefix, child->partial, sub_prefix);
prefix += sub_prefix;
}
// Store the prefix in the child
memcpy(child->partial, node->n.partial, min(prefix, ART_MAX_PREFIX_LEN));
child->partial_len += node->n.partial_len + 1;
}
*ref = child;
} else if (!depth && node->n.num_children == 0) {
//This happens if we have a fat root with the empty key.
//If only the empty key remains, then the fat root has zero children
node->children[0] = nullptr;
}
}
void art_tree::remove_child(art_node *n, art_node **ref, unsigned char c, art_node **l, int depth) {
switch (n->type) {
case ART_NODE4_KV:
case ART_NODE4:
return remove_child4((art_node4 *) n, ref, l, depth);
case ART_NODE16_KV:
case ART_NODE16:
return remove_child16((art_node16 *) n, ref, l);
case ART_NODE48_KV:
case ART_NODE48:
return remove_child48((art_node48 *) n, ref, c);
case ART_NODE256_KV:
case ART_NODE256:
return remove_child256((art_node256 *) n, ref, c);
default:
UNSTOPPABLE_ASSERT(false);
}
}
//NB: Here, n is the fat node from which we remove the kv/pair
void art_tree::remove_fat_child(art_node *n, art_node **ref, int depth) {
switch (n->type) {
case ART_NODE4_KV:
return remove_fat_child4((art_node4_kv *) n, ref, depth);
case ART_NODE16_KV:
return remove_fat_child16((art_node16_kv *) n, ref);
case ART_NODE48_KV:
return remove_fat_child48((art_node48_kv *) n, ref);
case ART_NODE256_KV:
return remove_fat_child256((art_node256_kv *) n, ref);
default:
UNSTOPPABLE_ASSERT(false);
}
}
void art_tree::copy_header(art_node *dest, art_node *src) {
dest->num_children = src->num_children;
dest->partial_len = src->partial_len;
memcpy(dest->partial, src->partial, min(ART_MAX_PREFIX_LEN, src->partial_len));
}
void art_tree::erase(const art_iterator &it) {
recursive_delete_binary(this->root, &this->root, it.key(), 0);
}
art_leaf *art_tree::iterative_insert(art_node *root, art_node **root_ptr, KeyRef &k, void *value,
int depth, int *old, int replace_existing) {
art_node *n = root;
art_node **ref = root_ptr;
//Ref is the memory location of the father that stores the pointer to the child in which we add the new item
//Of course, the root is not the child of anybody. We need the ptr to root bc it is possible that the root itself
//Grows by adding nodes, and hence gets relocated. Then, we need to update the ptr to the root
while (n) {
if (ART_IS_LEAF(n)) {
return insert_leaf(n, ref, k, value, depth, old, replace_existing);
}
art_leaf *min_of_n = nullptr;
if (n->partial_len) {
// Determine if the prefixes differ, since we need to split
int prefix_diff = prefix_mismatch(n, k, depth, &min_of_n);
if ((uint32_t) prefix_diff >= n->partial_len) {
depth += n->partial_len;
//handle fat key or go in depth
} else {
return insert_internal_node(n, ref, k, value, depth, old, min_of_n, prefix_diff, replace_existing);
}
}
if (k.size() == (depth)) {
return insert_fat_node(n, ref, k, value, depth, old, min_of_n, replace_existing);
}
// Find a child to recurse to
//Child is the pointer to the memory location within the node that contains the ptr to the child
art_node **child = find_child(n, ((unsigned char *) k.begin())[depth]);
if (!child) {
break;
}
//Else go on. Update depth, the current node and its reference in the list of children in the parent
depth++;
ref = child;
n = *ref;
}
return insert_child(n, ref, k, value, depth, old, replace_existing);
}
art_leaf *art_tree::insert_child(art_node *n, art_node **ref, const KeyRef &k, void *value, int depth,
int *old, int replace_existing) {
// No child, node goes within us
art_leaf *l = make_leaf(k, value);
const unsigned char *key = (const unsigned char *) k.begin();
add_child(n, ref, key[depth], SET_LEAF(l));
//After adding a child, the node might have grown (and old pointer n becomes invalid)
art_node *new_node = *ref;
art_node *pn = nullptr;
art_leaf *lm = nullptr;
int prev_next = art_next_prev(new_node, key[depth], &pn);
if (prev_next == ART_NEXT) {
//If the char of this key is NOT the maximum in the node, take the key's next node from curr_node
//If the next node exists, then the MIN of the next node is the new_key's next
//NB: The fat leaf cannot be the next, so we search for the min in the subtree
lm = minimum(pn);
//new key is LOWER than min
insert_before(l, lm);
} else if (prev_next == ART_PREV) {
//If the next does not exist, it means there is a prev (the curr_node has at least one child).
//The curr key is the next of the MAX of the prev node
//Check if the prev is the fat_leaf
if (pn == new_node) {
lm = ART_FAT_NODE_LEAF(new_node);
} else {
lm = maximum(pn);
}
//new key is BIGGER than lm
insert_after(l, lm);
}//if it is ART_NEITHER, then there's no prev nor next. They have been set to nullptr already
return l;
}
int art_tree::art_next_prev(art_node *n, unsigned char c, art_node **out) {
find_next(n, c, out);
if (*out) {
return ART_NEXT;
}
find_prev(n, c, out);
if (*out) {
return ART_PREV;
}
return ART_NEITHER;
}
art_leaf *art_tree::insert_internal_node(art_node *n, art_node **ref, const KeyRef &k, void *value, int depth,
int *old, art_leaf *min_of_n, int prefix_diff, int replace_existing) {
art_node4 *new_node;
bool kv_creat = (prefix_diff == (k.size() - depth));
if (!kv_creat) {
new_node = (art_node4 *) alloc_node(ART_NODE4);
*ref = (art_node *) new_node;
new_node->n.partial_len = prefix_diff;
memcpy(new_node->n.partial, n->partial, min(ART_MAX_PREFIX_LEN, prefix_diff));
// Adjust the prefix of the old node
if (n->partial_len <= ART_MAX_PREFIX_LEN) {
add_child4(new_node, ref, n->partial[prefix_diff], n);
n->partial_len -= (prefix_diff + 1);
memmove(n->partial, n->partial + prefix_diff + 1,
min(ART_MAX_PREFIX_LEN, n->partial_len));
} else {
n->partial_len -= (prefix_diff + 1);
art_leaf *l = min_of_n == nullptr ? minimum(n) : min_of_n;
min_of_n = l;
unsigned char *lkey = (unsigned char *) l->key.begin();
add_child4(new_node, ref, lkey[depth + prefix_diff], n);
memcpy(n->partial, lkey + depth + prefix_diff + 1,
min(ART_MAX_PREFIX_LEN, n->partial_len));
}
// Insert the new leaf
art_leaf *l = make_leaf(k, value);
add_child4(new_node, ref, ((unsigned char *) k.begin())[depth + prefix_diff], SET_LEAF(l));
art_node *pn;
art_leaf *lm = nullptr;
int prev_next = art_next_prev((art_node *) new_node, l->key[depth + prefix_diff], &pn);
if (prev_next == ART_NEXT) {
//If the char of this key is NOT the maximum in the node, take the key's next node from curr_node
//If the next node exists, then the MIN of the next node is the new_key's next
lm = minimum(pn);
insert_before(l, lm);
} else if (prev_next == ART_PREV) {
//If the next does not exist, it means there is a prev (the curr_node has at least one child).
//The curr key is the next of the MAX of the prev node
//We do not check for fat node
lm = maximum(pn);
//new key is BIGGER than lm
insert_after(l, lm);
}
return l;
} else {
//The new key becomes a fat node that has as child the current internal node.
//The current internal node has to be indexed by the first char in the prefix, whose size has to be reduced
//By one accordingly
new_node = (art_node4 *) alloc_kv_node(ART_NODE4_KV);
ART_FAT_NODE_LEAF(&new_node->n) = make_leaf(k, value);
//This is legacy code. I think it is valid, but probably it can be simplified in our case
*ref = (art_node *) new_node;
new_node->n.partial_len = prefix_diff;
memcpy(new_node->n.partial, n->partial, min(ART_MAX_PREFIX_LEN, prefix_diff));
// Adjust the prefix of the old node
if (n->partial_len <= ART_MAX_PREFIX_LEN) {
add_child4(new_node, ref, n->partial[prefix_diff], n);
n->partial_len -= (prefix_diff + 1);
memmove(n->partial, n->partial + prefix_diff + 1, min(ART_MAX_PREFIX_LEN, n->partial_len));
} else {
n->partial_len -= (prefix_diff + 1);
art_leaf *l = min_of_n == nullptr ? minimum(n) : min_of_n;//minimum(n);
min_of_n = l;
add_child4(new_node, ref, ((unsigned char *) l->key.begin())[depth + prefix_diff], n);
memcpy(n->partial, l->key.begin() + depth + prefix_diff + 1, min(ART_MAX_PREFIX_LEN, n->partial_len));
}
//Fat leaf is the smallest in this subtree. So the minimum in the subtree is its next
art_leaf *lm = min_of_n == nullptr ? minimum(n) : min_of_n;//minimum(n); //FIXME: reuse from before if already taken
min_of_n = lm;
//new key is LOWER than min
art_leaf *l_new = ART_FAT_NODE_LEAF(&new_node->n);
insert_before(l_new, lm);
return l_new;
}
}
art_leaf *art_tree::insert_fat_node(art_node *n, art_node **ref, const KeyRef &k, void *value, int depth,
int *old, art_leaf *min_of_n, int replace_existing) {
if (n->type >= ART_NODE4_KV) {
//If the node is already fat, it means you already have the key
*old = 1;
art_leaf *l = ART_FAT_NODE_LEAF(n);
if (replace_existing) {
l->value = value;
}
return l;
} else {
//We have to transform a node into a fat node
//The minimum function considers the leaf to be the minimum.
//Let's grab the minimum BEFORE we create the fat node and insert the new leaf :)
art_leaf *lm = min_of_n == nullptr ? minimum(n) : min_of_n;
art_node *nkv = n;
//change the type before deferencing the leaf
nkv->type = static_cast<ART_NODE_TYPE>(n->type + 4);
art_leaf *l_new = make_leaf(k, value);
ART_FAT_NODE_LEAF(nkv) = l_new;
*ref = (art_node *) nkv;
//Fat leaf is the smallest in this subtree. So the minimum in the subtree is its next
//new key is LOWER than min
if (lm) insert_before(l_new, lm);
return l_new;
}
}
art_leaf *art_tree::insert_leaf(art_node *n, art_node **ref, const KeyRef &k, void *value, int depth,
int *old, int replace_existing) {
art_leaf *l = ART_LEAF_RAW(n);
// Check if we are updating an existing value
//Original case
if (!leaf_matches(l, k, depth)) {
*old = 1;
if (replace_existing) {
l->value = value;
}
return l;
}
const unsigned char *key = (const unsigned char *) k.begin();
const int key_len = k.size();
int longest_prefix = longest_common_prefix(k, l->key, depth);
int kv_creat = (longest_prefix == (min(key_len, l->key.size()) - depth));
if (!kv_creat) {//Common case, old code
//Recompute longest prefix from depth. Probably can be optimized
// New value, we must split the leaf into a node4
art_node4 *new_node = (art_node4 *) alloc_node(ART_NODE4);
// Create a new leaf
art_leaf *l2 = make_leaf(k, value);
// Determine longest prefix
new_node->n.partial_len = longest_prefix;
memcpy(new_node->n.partial, key + depth, min(ART_MAX_PREFIX_LEN, longest_prefix));
// Add the leaves to the new node4
*ref = (art_node *) new_node;
add_child4(new_node, ref, l->key[depth + longest_prefix], SET_LEAF(l));
add_child4(new_node, ref, l2->key[depth + longest_prefix], SET_LEAF(l2));
//Set next and prev. Check if new leaf goes before or after existing leaf
if (l2->key[depth + longest_prefix] < l->key[depth + longest_prefix]) {
//New key comes BEFORE existing key
insert_before(l2, l);
} else {
//New key comes AFTER existing key
insert_after(l2, l);
}
return l2;
}
// The new key is a superset of the key in the leaf.
// So the current leaf becomes the value of the kv node
if (key_len > l->key.size()) {
art_node4_kv *new_node = (art_node4_kv *) alloc_kv_node(ART_NODE4_KV);
// Create a new leaf with the new key
art_leaf *l2 = make_leaf(k, value);
// Determine longest prefix
new_node->n.n.partial_len = longest_prefix;
memcpy(new_node->n.n.partial, key + depth, min(ART_MAX_PREFIX_LEN, longest_prefix));
// Add the leaf to the new node4
*ref = (art_node *) new_node;
add_child4((art_node4 * ) & new_node->n, ref, l2->key[depth + longest_prefix], SET_LEAF(l2));
ART_FAT_NODE_LEAF(&new_node->n.n) = l;
art_leaf *fat_leaf = ART_FAT_NODE_LEAF(&new_node->n.n);
//The new key goes in the leaf and its predecessor is the key in the new fat node
insert_after(l2, fat_leaf);
return l2;
} else {
// The key in the leaf is a supertset of the new key
// So the leaf stays a leaf and the new key goes in the kv_node
art_node4_kv *new_node = (art_node4_kv *) alloc_kv_node(ART_NODE4_KV);
art_leaf *fat_leaf = make_leaf(k, value);
ART_FAT_NODE_LEAF(&new_node->n.n) = fat_leaf;
new_node->n.n.partial_len = longest_prefix;
memcpy(new_node->n.n.partial, key + depth, min(ART_MAX_PREFIX_LEN, longest_prefix));
*ref = (art_node *) new_node;
add_child4((art_node4 * ) & new_node->n, ref, l->key[depth + longest_prefix], SET_LEAF(l));
//The fat node is the prev of the current leaf
insert_before(fat_leaf, l);
return fat_leaf;
}
}
int art_tree::longest_common_prefix(const KeyRef &k1, const KeyRef &k2, int depth) {
int max_cmp = min(k1.size(), k2.size()) - depth;
int idx;
for (idx = 0; idx < max_cmp; idx++) {
if (((unsigned char *) k1.begin())[depth + idx] != ((unsigned char *) k2.begin())[depth + idx])
return idx;
}
return idx;
}
void art_tree::insert_before(art_leaf *l_new, art_leaf *l_existing) {
l_new->next = l_existing;
if (l_existing) {
l_new->prev = l_existing->prev;
if (l_existing->prev) {
l_existing->prev->next = l_new;
}
l_existing->prev = l_new;
} else {
l_new->prev = nullptr;
}
}
void art_tree::insert_after(art_leaf *l_new, art_leaf *l_existing) {
l_new->prev = l_existing;
if (l_existing) {
l_new->next = l_existing->next;
if (l_existing->next) {
l_existing->next->prev = l_new;
}
l_existing->next = l_new;
} else {
l_new->next = nullptr;
}
}
void art_tree::add_child(art_node *n, art_node **ref, unsigned char c, void *child) {
switch (n->type) {
case ART_NODE4_KV:
case ART_NODE4:
return add_child4((art_node4 *) n, ref, c, child);
case ART_NODE16_KV:
case ART_NODE16:
return add_child16((art_node16 *) n, ref, c, child);
case ART_NODE48_KV:
case ART_NODE48:
return add_child48((art_node48 *) n, ref, c, child);
case ART_NODE256_KV:
case ART_NODE256:
return add_child256((art_node256 *) n, ref, c, child);
default:
UNSTOPPABLE_ASSERT(false);
}
}
void art_tree::add_child256(art_node256 *n, art_node **ref, unsigned char c, void *child) {
(void) ref;
n->n.num_children++;
n->children[c] = (art_node *) child;
}
void art_tree::add_child48(art_node48 *n, art_node **ref, unsigned char c, void *child) {
if (n->n.num_children < 48) {
int pos = 0;
while (n->children[pos]) pos++;
n->children[pos] = (art_node *) child;
n->keys[c] = pos + 1;
n->n.num_children++;
} else {
art_node256 *new_node;
//Copy the fat leaf pointer if needed
if (n->n.type == ART_NODE48_KV) {
new_node = (art_node256 *) alloc_node(ART_NODE256_KV);
ART_FAT_NODE_LEAF(&new_node->n) = ART_FAT_NODE_LEAF(&n->n);
} else {
new_node = (art_node256 *) alloc_node(ART_NODE256);
}
for (int i = 0; i < 256; i++) {
if (n->keys[i]) {
new_node->children[i] = n->children[n->keys[i] - 1];
}
}
copy_header((art_node *) new_node, (art_node *) n);
*ref = (art_node *) new_node;
add_child256(new_node, ref, c, child);
}
}
void art_tree::add_child16(art_node16 *n, art_node **ref, unsigned char c, void *child) {
if (n->n.num_children < 16) {
__m128i cmp;
// Compare the key to all 16 stored keys
cmp = _mm_cmplt_epu8(_mm_set1_epi8(c),
_mm_loadu_si128((__m128i *) n->keys));
// Use a mask to ignore children that don't exist
unsigned mask = (1 << n->n.num_children) - 1;
unsigned bitfield = _mm_movemask_epi8(cmp) & mask;
// Check if less than any
unsigned idx;
if (bitfield) {
idx = ctz(bitfield);
memmove(n->keys + idx + 1, n->keys + idx, n->n.num_children - idx);
memmove(n->children + idx + 1, n->children + idx,
(n->n.num_children - idx) * sizeof(void *));
} else
idx = n->n.num_children;
// Set the child
n->keys[idx] = c;
n->children[idx] = (art_node *) child;
n->n.num_children++;
} else {
art_node48 *new_node;
//Check whether this is a fat node
if (n->n.type == ART_NODE16_KV) {
new_node = (art_node48 *) alloc_node(ART_NODE48_KV);
ART_FAT_NODE_LEAF(&new_node->n) = ART_FAT_NODE_LEAF(&n->n);
} else {
new_node = (art_node48 *) alloc_node(ART_NODE48);
}
// Copy the child pointers and populate the key map
memcpy(new_node->children, n->children,
sizeof(void *) * n->n.num_children);
for (int i = 0; i < n->n.num_children; i++) {
new_node->keys[n->keys[i]] = i + 1;
}
copy_header((art_node *) new_node, (art_node *) n);
*ref = (art_node *) new_node;
add_child48(new_node, ref, c, child);
}
}
void art_tree::add_child4(art_node4 *n, art_node **ref, unsigned char c, void *child) {
if (n->n.num_children < 4) {
int idx;
for (idx = 0; idx < n->n.num_children; idx++) {
if (c < n->keys[idx]) break;
}
// Shift to make room
memmove(n->keys + idx + 1, n->keys + idx, n->n.num_children - idx);
memmove(n->children + idx + 1, n->children + idx, (n->n.num_children - idx) * sizeof(void *));
// Insert element
n->keys[idx] = c;
n->children[idx] = (art_node *) child;
n->n.num_children++;
} else {
art_node16 *new_node;
//Check whether this is a fat node
if (n->n.type == ART_NODE4_KV) {
new_node = (art_node16 *) alloc_node(ART_NODE16_KV);
ART_FAT_NODE_LEAF(&new_node->n) = ART_FAT_NODE_LEAF(&n->n);
} else {
new_node = (art_node16 *) alloc_node(ART_NODE16);
}
// Copy the child pointers and the key map
memcpy(new_node->children, n->children, sizeof(void *) * n->n.num_children);
memcpy(new_node->keys, n->keys, sizeof(unsigned char) * n->n.num_children);
copy_header((art_node *) new_node, (art_node *) n);
*ref = (art_node *) new_node;
add_child16(new_node, ref, c, child);
}
}
//Every node is actually a kv node, but the type is <= NODE256
art_node *art_tree::alloc_node(ART_NODE_TYPE type) {
const int offset = type > ART_NODE256 ? 0 : ART_NODE256;
art_node *n = (art_node *)
new((Arena & ) * this->arena)uint8_t[node_sizes[offset + type]]();
n->type = type;
return n;
}
art_node *art_tree::alloc_kv_node(ART_NODE_TYPE type) {
art_node *n = (art_node *)
new((Arena & ) * this->arena)uint8_t[node_sizes[type]]();
n->type = type;
return n;
}
art_leaf *art_tree::make_leaf(const KeyRef &k, void *value) {
const int key_len = k.size();
//Allocate contiguous buffer to hold the leaf and the key pointed by the KeyRef
art_leaf *v = (art_leaf *)
new((Arena & ) * this->arena)uint8_t[sizeof(art_leaf) + key_len];
//copy the key to the proper offset in the buffer
memcpy(v + 1, k.begin(), key_len);
KeyRef nkr = KeyRef((const uint8_t *) (v + 1), key_len);
//create the art_leaf, allocating it on the buffer
//The KeyRef& passed as argument is the new one, allocated in the buffer
art_leaf *l = new(v)art_leaf(nkr, value);
l->prev = nullptr;
l->next = nullptr;
l->type = ART_LEAF;
return l;
}
int art_tree::prefix_mismatch(art_node *n, KeyRef &k, int depth, art_leaf **minout) {
const int key_len = k.size();
const unsigned char *key = (const unsigned char *) k.begin();
int max_cmp = min(min(ART_MAX_PREFIX_LEN, n->partial_len), key_len - depth);
int idx;
for (idx = 0; idx < max_cmp; idx++) {
if (n->partial[idx] != key[depth + idx])
return idx;
}
// If the prefix is short we can avoid finding a leaf
if (n->partial_len > ART_MAX_PREFIX_LEN) {
// Prefix is longer than what we've checked, find a leaf
art_leaf *l = minimum(n);
*minout = l;
max_cmp = min(l->key.size(), key_len) - depth;
for (; idx < max_cmp; idx++) {
if (l->key.begin()[idx + depth] != k.begin()[depth + idx])
return idx;
}
}
return idx;
}
//Find the child corresponding to c, if present, and the largest child smaller than c
void art_tree::find_prev(art_node *n, unsigned char c, art_node **out) {
int i, mask, bitfield;
*out = nullptr;
union {
art_node4 *p1;
art_node16 *p2;
art_node48 *p3;
art_node256 *p4;
} p;
switch (n->type) {
case ART_NODE4_KV:
case ART_NODE4:
p.p1 = (art_node4 *) n;
for (i = 0; i < n->num_children; i++) {
if (p.p1->keys[i] < c) {
*out = p.p1->children[i];
} else {
break;
}
}
if (i == 0 && n->type == ART_NODE4_KV) {
*out = n;
}
break;
{
__m128i cmp;
case ART_NODE16_KV:
case ART_NODE16:
p.p2 = (art_node16 *) n;
// Compare the key to all 16 stored keys for less than
cmp = _mm_cmpgt_epu8(_mm_set1_epi8(c), _mm_loadu_si128((__m128i *) p.p2->keys));
// Use a mask to ignore children that don't exist
mask = (1 << n->num_children) - 1;
bitfield = _mm_movemask_epi8(cmp) & mask;
if (bitfield) {
//We have at least one bit set to one, so the largest smaller exists
int one = clz(bitfield);
one = (sizeof(bitfield) * 8) - one;
*out = p.p2->children[one - 1];
} else {
if (n->type == ART_NODE16_KV) {
*out = n;
}
}
break;
}
case ART_NODE48_KV:
case ART_NODE48: {
p.p3 = (art_node48 *) n;
unsigned char cc = c - 1;
while (cc < 255) {
i = p.p3->keys[cc];
if (i) {
*out = p.p3->children[i - 1];
break;
}
--cc;
}
if (cc == 255 && n->type == ART_NODE48_KV) {
*out = n;
}
break;
}
case ART_NODE256_KV:
case ART_NODE256: {
p.p4 = (art_node256 *) n;
unsigned char cc = c - 1;
if (c == 0 && n->type == ART_NODE256_KV) {
*out = n;
}
while (cc < 255) {
if (p.p4->children[cc]) {
*out = p.p4->children[cc];
break;
}
--cc;
}
break;
}
default:
UNSTOPPABLE_ASSERT(false);
}
}
#endif //ART_IMPL_H
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