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115 lines
3.2 KiB
C
115 lines
3.2 KiB
C
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#include <lighttpd/idlist.h>
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#define UL_BITS (sizeof(gulong) * 8)
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/* There are often no explicit bit shifts used in this code. This is on purpose, the
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* code looks much cleaner without them, the correct constant for *, / and % is easier to calculate
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* as constant (UL_BITS) and the compiler should know how to optimize the operations; as UL_BITS is hopefully
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* of the form 2^n this should result in bit shifts in the executable code.
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*/
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liIDList* li_idlist_new(gint max_ids) {
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liIDList *l = g_slice_new0(liIDList);
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g_assert(max_ids > 0);
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l->bitvector = g_array_new(FALSE, TRUE, sizeof(gulong));
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l->max_ids = max_ids;
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l->next_free_id = -1;
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l->used_ids = 0;
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return l;
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}
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void li_idlist_free(liIDList *l) {
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if (!l) return;
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g_array_free(l->bitvector, TRUE);
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g_slice_free(liIDList, l);
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}
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static void mark_bit(GArray *a, gint id) {
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guint ndx = id / UL_BITS, bndx = id % UL_BITS;
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gulong bmask = 1 << bndx;
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g_assert(id >= 0 && ndx < a->len);
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g_assert(0 == (g_array_index(a, gulong, ndx) & (bmask))); /* bit musn't be set */
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g_array_index(a, gulong, ndx) |= (bmask);
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}
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static void clear_bit(GArray *a, gint id) {
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guint ndx = id / UL_BITS, bndx = id % UL_BITS;
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gulong bmask = 1 << bndx;
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g_assert(id >= 0 && ndx < a->len);
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g_assert(0 != (g_array_index(a, gulong, ndx) & (bmask))); /* bit must be set */
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g_array_index(a, gulong, ndx) &= ~(bmask);
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}
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static void idlist_reserve(GArray *a, guint id) {
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guint ndx = id / UL_BITS;
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if (ndx >= a->len) g_array_set_size(a, ndx+1);
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}
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gint li_idlist_get(liIDList *l) {
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guint fndx, ndx;
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gint newid, bndx;
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gulong u = -1;
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GArray *a = l->bitvector;
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if (l->used_ids >= l->max_ids) return -1;
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if (l->next_free_id < 0) { /* all ids in use */
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newid = l->used_ids++;
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idlist_reserve(a, newid);
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mark_bit(a, newid);
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return newid;
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}
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/* search for an array entry which doesn't have all bits set (i.e. != (gulong) -1)
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* start with the entry of next_free_id, all below are in use anyway
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*/
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fndx = l->next_free_id / UL_BITS;
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for (ndx = fndx; ndx < a->len && ((gulong) -1 == (u = g_array_index(a, gulong, ndx))); ndx++) ;
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if (ndx == a->len) { /* again: all ids are in use */
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l->next_free_id = -1;
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newid = l->used_ids++;
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idlist_reserve(a, newid);
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mark_bit(a, newid);
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return newid;
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}
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/* array entry != -1, search for free bit */
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if (fndx == ndx) bndx = (l->next_free_id / UL_BITS) - 1;
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else bndx = -1;
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bndx = g_bit_nth_lsf(~u, bndx);
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/* 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 */
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g_assert(bndx != -1);
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newid = ndx * UL_BITS + bndx;
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if (newid == (gint) l->used_ids) {
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l->next_free_id = -1;
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} else {
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l->next_free_id = newid+1;
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}
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l->used_ids++;
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mark_bit(a, newid);
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return newid;
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}
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gboolean li_idlist_is_used(liIDList *l, gint id) {
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GArray *a = l->bitvector;
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guint ndx = id / UL_BITS, bndx = id % UL_BITS;
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gulong bmask = 1 << bndx;
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if (id < 0 || ndx >= a->len) return FALSE;
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return (0 != (g_array_index(a, gulong, ndx) & (bmask)));
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}
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void li_idlist_put(liIDList *l, gint id) {
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clear_bit(l->bitvector, id);
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l->used_ids--;
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if ((l->next_free_id < 0 && (guint) id < l->used_ids) || id < l->next_free_id) l->next_free_id = id;
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}
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