add a generic priority queue implementation

src/pulsecore/prioq.c

@@ -0,0 +1,255 @@
+/***
+  This file is part of PulseAudio.
+
+  Copyright 2008 Lennart Poettering
+
+  PulseAudio is free software; you can redistribute it and/or modify
+  it under the terms of the GNU Lesser General Public License as published
+  by the Free Software Foundation; either version 2 of the License,
+  or (at your option) any later version.
+
+  PulseAudio is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with PulseAudio; if not, write to the Free Software
+  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
+  USA.
+***/
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <pulse/xmalloc.h>
+
+#include <pulsecore/flist.h>
+
+#include "prioq.h"
+
+struct pa_prioq_item {
+    void *value;
+    unsigned idx;
+};
+
+struct pa_prioq {
+    pa_prioq_item **items;
+    unsigned n_items;
+    unsigned n_allocated;
+    pa_compare_func_t compare_func;
+};
+
+PA_STATIC_FLIST_DECLARE(items, 0, pa_xfree);
+
+pa_prioq *pa_prioq_new(pa_compare_func_t compare_func) {
+
+    pa_prioq *q;
+
+    q = pa_xnew(pa_prioq, 1);
+    q->compare_func = compare_func;
+    q->n_items = 0;
+    q->n_allocated = 64;
+    q->items = pa_xnew(pa_prioq_item*, q->n_allocated);
+
+    return q;
+}
+
+void pa_prioq_free(pa_prioq *q, pa_free2_cb_t free_cb, void *userdata) {
+    pa_prioq_item **i, **e;
+
+    pa_assert(q);
+
+    for (i = q->items, e = q->items + q->n_items; i < e; i++) {
+
+        if (!*i)
+            continue;
+
+        if (free_cb)
+            free_cb((*i)->value, userdata);
+
+        pa_xfree(*i);
+    }
+
+    pa_xfree(q->items);
+    pa_xfree(q);
+}
+
+static void shuffle_up(pa_prioq *q, pa_prioq_item *i) {
+    pa_assert(q);
+    pa_assert(i);
+
+    j = i->idx;
+
+    while (j > 0) {
+        unsigned k;
+
+        k = (j-1)/2;
+
+        if (q->compare_func(q->items[k]->value, i->value) < 0)
+            break;
+
+        q->items[k]->idx = j;
+        q->items[j] = q->items[k];
+
+        j = k;
+    }
+
+    i->idx = j;
+    q->items[j] = i;
+
+}
+
+pa_prioq_item* pa_prioq_put(pa_prioq *q, void *p) {
+    pa_prioq_item *i;
+    unsigned j;
+
+    pa_assert(q);
+
+    if (q->n_items >= q->n_allocated) {
+        q->n_allocated = PA_MAX(q->n_items+1, q->n_allocated)*2;
+        q->items = pa_xrealloc(q->items, sizeof(pa_prioq_item*) * q->n_allocated);
+    }
+
+    if (!(i = pa_flist_pop(PA_STATIC_FLIST_GET(items))))
+        i = pa_xnew(pa_prioq_item, 1);
+
+    i->value = p;
+    i->idx = q->n_items++;
+
+    shuffle_up(q, i);
+
+    return i;
+}
+
+void* pa_prioq_peek(pa_prioq *q) {
+    pa_assert(q);
+
+    if (q->n_items <= 0)
+        return NULL;
+
+    return q->items[0]->value;
+}
+
+void* pa_prioq_pop(pa_prioq *q){
+    pa_assert(q);
+
+    if (q->n_items <= 0)
+        return NULL;
+
+    return pa_prioq_remove(q, q->items[0]);
+}
+
+static void swap(pa_prioq *q, unsigned j, unsigned k) {
+    pa_prioq_item *t;
+
+    pa_assert(q);
+    pa_assert(j < q->n_items);
+    pa_assert(k < q->n_items);
+
+    pa_assert(q->items[j]->idx == j);
+    pa_assert(q->items[k]->idx == k);
+
+    t = q->items[j];
+
+    q->items[j]->idx = k;
+    q->items[j] = q->items[k];
+
+    q->items[k]->idx = j;
+    q->items[k] = t;
+}
+
+static void shuffle_down(pa_prioq *q, unsigned idx) {
+
+    pa_assert(q);
+    pa_assert(idx < q->n_items);
+
+    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]->value, q->items[idx]->value) < 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]->value, q->items[s]->value) < 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;
+    }
+}
+
+void* pa_prioq_remove(pa_prioq *q, pa_prioq_item *i) {
+    void *p;
+
+    pa_assert(q);
+    pa_assert(i);
+    pa_assert(q->n_items >= 1);
+
+    p = i->value;
+
+    if (q->n_items-1 == i->idx) {
+        /* We are the last entry, so let's just remove us and good */
+        q->n_items--;
+
+    } else {
+
+        /* We are not the last entry, we need to replace ourselves
+         * with the last node and reshuffle */
+
+        q->items[i->idx] = q->items[q->n_items-1];
+        q->items[i->idx]->idx = i->idx;
+        q->n_items--;
+
+        shuffle_down(q, i->idx);
+    }
+
+    if (pa_flist_push(PA_STATIC_FLIST_GET(items), i) < 0)
+        pa_xfree(i);
+
+    return p;
+}
+
+unsigned pa_prioq_size(pa_prioq *q) {
+    pa_assert(q);
+
+    return q->n_items;
+}
+
+pa_bool_t pa_prioq_isempty(pa_prioq *q) {
+    pa_assert(q);
+
+    return q->n_items == 0;
+}
+
+void pa_prioq_reshuffle(pa_prioq *q, pa_prioq_item *i) {
+    pa_assert(q);
+    pa_assert(i);
+
+    /* This will move the entry down as far as necessary */
+    shuffle_down(q, i->idx);
+
+    /* And this will move the entry up as far as necessary */
+    shuffle_up(q, i->idx);
+}