basic: add a Bitmap implementation

For when a Hashmap is overkill.

src/basic/bitmap.c

@@ -0,0 +1,208 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+/***
+  This file is part of systemd.
+
+  Copyright 2015 Tom Gundersen
+
+  systemd 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 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd 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
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include "util.h"
+
+#include "bitmap.h"
+
+struct Bitmap {
+        long long unsigned *bitmaps;
+        size_t n_bitmaps;
+        size_t bitmaps_allocated;
+        unsigned next_entry;
+};
+
+/* Bitmaps are only meant to store relatively small numbers
+ * (corresponding to, say, an enum), so it is ok to limit
+ * the max entry. 64k should be plenty. */
+#define BITMAPS_MAX_ENTRY 0xffff
+
+/* This indicates that we reached the end of the bitmap */
+#define BITMAP_END ((unsigned) -1)
+
+#define BITMAP_NUM_TO_OFFSET(n)           ((n) / (sizeof(long long unsigned) * 8))
+#define BITMAP_NUM_TO_REM(n)              ((n) % (sizeof(long long unsigned) * 8))
+#define BITMAP_OFFSET_TO_NUM(offset, rem) ((offset) * sizeof(long long unsigned) * 8 + (rem))
+
+Bitmap *bitmap_new(void) {
+        return new0(Bitmap, 1);
+}
+
+void bitmap_free(Bitmap *b) {
+        if (!b)
+                return;
+
+        free(b->bitmaps);
+        free(b);
+}
+
+int bitmap_ensure_allocated(Bitmap **b) {
+        Bitmap *a;
+
+        if (*b)
+                return 0;
+
+        a = bitmap_new();
+        if (!a)
+                return -ENOMEM;
+
+        *b = a;
+
+        return 0;
+}
+
+int bitmap_set(Bitmap *b, unsigned n) {
+        long long bitmask;
+        unsigned offset;
+
+        assert(b);
+
+        /* we refuse to allocate huge bitmaps */
+        if (n > BITMAPS_MAX_ENTRY)
+                return -ERANGE;
+
+        offset = BITMAP_NUM_TO_OFFSET(n);
+
+        if (offset >= b->n_bitmaps) {
+                if (!GREEDY_REALLOC0(b->bitmaps, b->bitmaps_allocated, offset + 1))
+                        return -ENOMEM;
+
+                b->n_bitmaps = offset + 1;
+        }
+
+        bitmask = 1 << BITMAP_NUM_TO_REM(n);
+
+        b->bitmaps[offset] |= bitmask;
+
+        return 0;
+}
+
+void bitmap_unset(Bitmap *b, unsigned n) {
+        long long bitmask;
+        unsigned offset;
+
+        assert(b);
+
+        offset = BITMAP_NUM_TO_OFFSET(n);
+
+        if (offset >= b->n_bitmaps)
+                return;
+
+        bitmask = 1 << BITMAP_NUM_TO_REM(n);
+
+        b->bitmaps[offset] &= ~bitmask;
+}
+
+bool bitmap_isset(Bitmap *b, unsigned n) {
+        long long bitmask;
+        unsigned offset;
+
+        if (!b || !b->bitmaps)
+                return false;
+
+        offset = BITMAP_NUM_TO_OFFSET(n);
+
+        if (offset >= b->n_bitmaps)
+                return false;
+
+        bitmask = 1 << BITMAP_NUM_TO_REM(n);
+
+        return !!(b->bitmaps[offset] & bitmask);
+}
+
+bool bitmap_isclear(Bitmap *b) {
+        unsigned i;
+
+        assert(b);
+
+        for (i = 0; i < b->n_bitmaps; i++)
+                if (b->bitmaps[i])
+                        return false;
+
+        return true;
+}
+
+void bitmap_clear(Bitmap *b) {
+        unsigned i;
+
+        assert(b);
+
+        for (i = 0; i < b->n_bitmaps; i++)
+                b->bitmaps[i] = 0;
+}
+
+void bitmap_rewind(Bitmap *b) {
+        if (!b)
+                return;
+
+        b->next_entry = 0;
+}
+
+bool bitmap_next(Bitmap *b, unsigned *n) {
+        long long bitmask;
+        unsigned offset, rem;
+
+        if (!b && b->next_entry == BITMAP_END)
+                return false;
+
+        offset = BITMAP_NUM_TO_OFFSET(b->next_entry);
+        rem = BITMAP_NUM_TO_REM(b->next_entry);
+        bitmask = 1 << rem;
+
+        for (; offset < b->n_bitmaps; offset ++) {
+                if (b->bitmaps[offset]) {
+                        for (; bitmask; bitmask <<= 1, rem ++) {
+                                if (b->bitmaps[offset] & bitmask) {
+                                        *n = BITMAP_OFFSET_TO_NUM(offset, rem);
+                                        b->next_entry = *n + 1;
+
+                                        return true;
+                                }
+                        }
+                }
+
+                rem = 0;
+                bitmask = 1;
+        }
+
+        b->next_entry = BITMAP_END;
+
+        return false;
+}
+
+bool bitmap_equal(Bitmap *a, Bitmap *b) {
+        unsigned i;
+
+        if (!a ^ !b)
+                return false;
+
+        if (!a)
+                return true;
+
+        if (a->n_bitmaps != b->n_bitmaps)
+                return false;
+
+        for (i = 0; i < a->n_bitmaps; i++)
+                if (a->bitmaps[i] != b->bitmaps[i])
+                        return false;
+
+        return true;
+}