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Diffstat (limited to 'src/basic/prioq.c')
| -rw-r--r-- | src/basic/prioq.c | 309 |
1 files changed, 309 insertions, 0 deletions
diff --git a/src/basic/prioq.c b/src/basic/prioq.c new file mode 100644 index 0000000..5fbb999 --- /dev/null +++ b/src/basic/prioq.c @@ -0,0 +1,309 @@ +/* SPDX-License-Identifier: LGPL-2.1-or-later */ + +/* + * Priority Queue + * The prioq object implements a priority queue. That is, it orders objects by + * their priority and allows O(1) access to the object with the highest + * priority. Insertion and removal are Θ(log n). Optionally, the caller can + * provide a pointer to an index which will be kept up-to-date by the prioq. + * + * The underlying algorithm used in this implementation is a Heap. + */ + +#include <errno.h> +#include <stdlib.h> + +#include "alloc-util.h" +#include "hashmap.h" +#include "prioq.h" + +struct prioq_item { + void *data; + unsigned *idx; +}; + +struct Prioq { + compare_func_t compare_func; + unsigned n_items, n_allocated; + + struct prioq_item *items; +}; + +Prioq *prioq_new(compare_func_t compare_func) { + Prioq *q; + + q = new(Prioq, 1); + if (!q) + return q; + + *q = (Prioq) { + .compare_func = compare_func, + }; + + return q; +} + +Prioq* prioq_free(Prioq *q) { + if (!q) + return NULL; + + free(q->items); + return mfree(q); +} + +int prioq_ensure_allocated(Prioq **q, compare_func_t compare_func) { + assert(q); + + if (*q) + return 0; + + *q = prioq_new(compare_func); + if (!*q) + return -ENOMEM; + + return 0; +} + +static void swap(Prioq *q, unsigned j, unsigned k) { + assert(q); + assert(j < q->n_items); + assert(k < q->n_items); + + assert(!q->items[j].idx || *(q->items[j].idx) == j); + assert(!q->items[k].idx || *(q->items[k].idx) == k); + + SWAP_TWO(q->items[j].data, q->items[k].data); + SWAP_TWO(q->items[j].idx, q->items[k].idx); + + if (q->items[j].idx) + *q->items[j].idx = j; + + if (q->items[k].idx) + *q->items[k].idx = k; +} + +static unsigned shuffle_up(Prioq *q, unsigned idx) { + assert(q); + assert(idx < q->n_items); + + while (idx > 0) { + unsigned k; + + k = (idx-1)/2; + + if (q->compare_func(q->items[k].data, q->items[idx].data) <= 0) + break; + + swap(q, idx, k); + idx = k; + } + + return idx; +} + +static unsigned shuffle_down(Prioq *q, unsigned idx) { + assert(q); + + for (;;) { + unsigned j, k, s; + + k = (idx+1)*2; /* right child */ + j = k-1; /* left child */ + + if (j >= q->n_items) + break; + + if (q->compare_func(q->items[j].data, q->items[idx].data) < 0) + + /* So our left child is smaller than we are, let's + * remember this fact */ + s = j; + else + s = idx; + + if (k < q->n_items && + q->compare_func(q->items[k].data, q->items[s].data) < 0) + + /* So our right child is smaller than we are, let's + * remember this fact */ + s = k; + + /* s now points to the smallest of the three items */ + + if (s == idx) + /* No swap necessary, we're done */ + break; + + swap(q, idx, s); + idx = s; + } + + return idx; +} + +int prioq_put(Prioq *q, void *data, unsigned *idx) { + struct prioq_item *i; + unsigned k; + + assert(q); + + if (q->n_items >= q->n_allocated) { + unsigned n; + struct prioq_item *j; + + n = MAX((q->n_items+1) * 2, 16u); + j = reallocarray(q->items, n, sizeof(struct prioq_item)); + if (!j) + return -ENOMEM; + + q->items = j; + q->n_allocated = n; + } + + k = q->n_items++; + i = q->items + k; + i->data = data; + i->idx = idx; + + if (idx) + *idx = k; + + shuffle_up(q, k); + + return 0; +} + +int prioq_ensure_put(Prioq **q, compare_func_t compare_func, void *data, unsigned *idx) { + int r; + + r = prioq_ensure_allocated(q, compare_func); + if (r < 0) + return r; + + return prioq_put(*q, data, idx); +} + +static void remove_item(Prioq *q, struct prioq_item *i) { + struct prioq_item *l; + + assert(q); + assert(i); + + l = q->items + q->n_items - 1; + + if (i == l) + /* Last entry, let's just remove it */ + q->n_items--; + else { + unsigned k; + + /* Not last entry, let's replace the last entry with + * this one, and reshuffle */ + + k = i - q->items; + + i->data = l->data; + i->idx = l->idx; + if (i->idx) + *i->idx = k; + q->n_items--; + + k = shuffle_down(q, k); + shuffle_up(q, k); + } +} + +static struct prioq_item* find_item(Prioq *q, void *data, unsigned *idx) { + struct prioq_item *i; + + assert(q); + + if (q->n_items <= 0) + return NULL; + + if (idx) { + if (*idx == PRIOQ_IDX_NULL || + *idx >= q->n_items) + return NULL; + + i = q->items + *idx; + if (i->data != data) + return NULL; + + return i; + } else { + for (i = q->items; i < q->items + q->n_items; i++) + if (i->data == data) + return i; + return NULL; + } +} + +int prioq_remove(Prioq *q, void *data, unsigned *idx) { + struct prioq_item *i; + + if (!q) + return 0; + + i = find_item(q, data, idx); + if (!i) + return 0; + + remove_item(q, i); + return 1; +} + +void prioq_reshuffle(Prioq *q, void *data, unsigned *idx) { + struct prioq_item *i; + unsigned k; + + assert(q); + + i = find_item(q, data, idx); + if (!i) + return; + + k = i - q->items; + k = shuffle_down(q, k); + shuffle_up(q, k); +} + +void *prioq_peek_by_index(Prioq *q, unsigned idx) { + if (!q) + return NULL; + + if (idx >= q->n_items) + return NULL; + + return q->items[idx].data; +} + +void *prioq_pop(Prioq *q) { + void *data; + + if (!q) + return NULL; + + if (q->n_items <= 0) + return NULL; + + data = q->items[0].data; + remove_item(q, q->items); + return data; +} + +unsigned prioq_size(Prioq *q) { + + if (!q) + return 0; + + return q->n_items; +} + +bool prioq_isempty(Prioq *q) { + + if (!q) + return true; + + return q->n_items <= 0; +} |