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#include <lighttpd/idlist.h>
#define UL_BITS (sizeof(gulong) * 8)
/* There are often no explicit bit shifts used in this code. This is on purpose, the
* code looks much cleaner without them, the correct constant for *, / and % is easier to calculate
* as constant (UL_BITS) and the compiler should know how to optimize the operations; as UL_BITS is hopefully
* of the form 2^n this should result in bit shifts in the executable code.
*/
liIDList* li_idlist_new(gint max_ids) {
liIDList *l = g_slice_new0(liIDList);
g_assert(max_ids > 0);
l->bitvector = g_array_new(FALSE, TRUE, sizeof(gulong));
l->max_ids = max_ids;
l->next_free_id = -1;
l->used_ids = 0;
return l;
}
void li_idlist_free(liIDList *l) {
if (!l) return;
g_array_free(l->bitvector, TRUE);
g_slice_free(liIDList, l);
}
static void mark_bit(GArray *a, gint id) {
guint ndx = id / UL_BITS, bndx = id % UL_BITS;
gulong bmask = 1ul << bndx;
g_assert(id >= 0 && ndx < a->len);
g_assert(0 == (g_array_index(a, gulong, ndx) & (bmask))); /* bit musn't be set */
g_array_index(a, gulong, ndx) |= (bmask);
}
static void clear_bit(GArray *a, gint id) {
guint ndx = id / UL_BITS, bndx = id % UL_BITS;
gulong bmask = 1ul << bndx;
g_assert(id >= 0 && ndx < a->len);
g_assert(0 != (g_array_index(a, gulong, ndx) & (bmask))); /* bit must be set */
g_array_index(a, gulong, ndx) &= ~(bmask);
}
static void idlist_reserve(GArray *a, guint id) {
guint ndx = id / UL_BITS;
if (ndx >= a->len) g_array_set_size(a, ndx+1);
}
gint li_idlist_get(liIDList *l) {
guint fndx, ndx;
gint newid, bndx;
gulong u = -1;
GArray *a = l->bitvector;
if (l->used_ids >= l->max_ids) return -1;
if (l->next_free_id < 0) { /* all ids in use */
newid = l->used_ids++;
idlist_reserve(a, newid);
mark_bit(a, newid);
return newid;
}
/* search for an array entry which doesn't have all bits set (i.e. != (gulong) -1)
* start with the entry of next_free_id, all below are in use anyway
*/
fndx = l->next_free_id / UL_BITS;
for (ndx = fndx; ndx < a->len && ((gulong) -1 == (u = g_array_index(a, gulong, ndx))); ndx++) ;
if (ndx == a->len) { /* again: all ids are in use */
l->next_free_id = -1;
newid = l->used_ids++;
idlist_reserve(a, newid);
mark_bit(a, newid);
return newid;
}
/* array entry != -1, search for free bit */
if (fndx == ndx) bndx = (l->next_free_id / UL_BITS) - 1;
else bndx = -1;
bndx = g_bit_nth_lsf(~u, bndx);
/* no free bit found; should never happen as u != -1 and next_free_id should be correct, i.e. all bits <= the bit start index should be set */
g_assert(bndx != -1);
newid = ndx * UL_BITS + bndx;
if (newid == (gint) l->used_ids) {
l->next_free_id = -1;
} else {
l->next_free_id = newid+1;
}
l->used_ids++;
mark_bit(a, newid);
return newid;
}
gboolean li_idlist_is_used(liIDList *l, gint id) {
GArray *a = l->bitvector;
guint ndx = id / UL_BITS, bndx = id % UL_BITS;
gulong bmask = 1ul << bndx;
if (id < 0 || ndx >= a->len) return FALSE;
return (0 != (g_array_index(a, gulong, ndx) & (bmask)));
}
void li_idlist_put(liIDList *l, gint id) {
clear_bit(l->bitvector, id);
l->used_ids--;
if ((l->next_free_id < 0 && (guint) id < l->used_ids) || id < l->next_free_id) l->next_free_id = id;
}