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#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef uint32_t unset_t;
#define BITS_PER_WORD (sizeof(unset_t) * 8)
#define bits_unset(x) (BITS_PER_WORD - __builtin_popcount(x))
#define TREE_ARY 16
#define BITS_PER_LEAF (TREE_ARY * BITS_PER_WORD)
struct bitmap_tree {
struct {
uint64_t size;
uint64_t nr_unset;
size_t first_leaf;
} __attribute__((aligned(64)));
struct bitmap_tree_node {
unset_t nr_unset[TREE_ARY];
} tree[];
};
static void bitmap_tree_init(struct bitmap_tree *tree, size_t i,
uint64_t nr_unset, uint64_t nr_this_level)
{
struct bitmap_tree_node *n = tree->tree + i;
unsigned j = 0;
if (i < tree->first_leaf) {
i = TREE_ARY * i + 1;
nr_this_level /= TREE_ARY;
while (nr_unset) {
n->nr_unset[j] = nr_unset < nr_this_level
? nr_unset : nr_this_level;
bitmap_tree_init(tree, i + j, n->nr_unset[j],
nr_this_level);
nr_unset -= n->nr_unset[j];
j++;
}
} else {
memset(n, 0, sizeof(*n));
}
}
struct bitmap_tree *bitmap_tree_alloc(uint64_t size)
{
struct bitmap_tree *tree;
size_t nr_leaf_nodes = (size + BITS_PER_LEAF - 1) / BITS_PER_LEAF;
size_t nr_nodes = 0;
size_t nr_cur_level = 1;
while (1) {
if (nr_cur_level >= nr_leaf_nodes)
break;
nr_nodes += nr_cur_level;
nr_cur_level *= TREE_ARY;
}
nr_nodes += nr_leaf_nodes;
tree = malloc(sizeof(struct bitmap_tree) +
sizeof(struct bitmap_tree_node) * nr_nodes);
tree->size = size;
tree->nr_unset = size;
tree->first_leaf = nr_nodes - nr_leaf_nodes;
bitmap_tree_init(tree, 0, tree->nr_unset,
nr_cur_level * BITS_PER_LEAF);
return tree;
}
static uint64_t set_nth_unset_bit_recurse(struct bitmap_tree *tree, size_t i,
uint64_t bit_to_set)
{
struct bitmap_tree_node *n = tree->tree + i;
unsigned j = 0, bit = 0;
if (i < tree->first_leaf) {
i = TREE_ARY * i + 1;
__builtin_prefetch(tree->tree + i);
while (bit_to_set > n->nr_unset[j]) {
bit_to_set -= n->nr_unset[j];
j++;
}
n->nr_unset[j]--;
return set_nth_unset_bit_recurse(tree, i + j, bit_to_set);
} else {
while (bit_to_set > bits_unset(n->nr_unset[j])) {
bit_to_set -= bits_unset(n->nr_unset[j]);
j++;
}
do {
while (n->nr_unset[j] & (1ULL << bit))
bit++;
} while (bit_to_set--);
n->nr_unset[j] &= ~(1ULL << bit);
return ((i - tree->first_leaf) * TREE_ARY + j) * BITS_PER_WORD + bit;
}
}
uint64_t set_nth_unset_bit(struct bitmap_tree *tree, uint64_t bit)
{
bit %= tree->nr_unset;
tree->nr_unset--;
return set_nth_unset_bit_recurse(tree, 0, bit);
}
int main()
{
struct bitmap_tree *tree = bitmap_tree_alloc(123320987);
while (tree->nr_unset)
set_nth_unset_bit(tree, lrand48());
return 0;
}
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