+
+#define BB_SLOT_SIZE (16*1024) /* Desired size in bytes */
+#define BB_PER_SLOT_BITS (BB_SLOT_SIZE * 8) /* Number of bits per slot */
+#define BB_PER_SLOT_INTS (BB_SLOT_SIZE / 4) /* Number of int32s per slot */
+
+struct bitbag {
+ uint32 **bits;
+ int slot_cnt;
+};
+
+struct bitbag *bitbag_create(int max_ndx)
+{
+ struct bitbag *bb = new(struct bitbag);
+ bb->slot_cnt = (max_ndx + BB_PER_SLOT_BITS - 1) / BB_PER_SLOT_BITS;
+
+ if (!(bb->bits = (uint32**)calloc(bb->slot_cnt, sizeof (uint32*))))
+ out_of_memory("bitbag_create");
+
+ return bb;
+}
+
+void bitbag_set_bit(struct bitbag *bb, int ndx)
+{
+ int slot = ndx / BB_PER_SLOT_BITS;
+ ndx %= BB_PER_SLOT_BITS;
+
+ if (!bb->bits[slot]) {
+ if (!(bb->bits[slot] = (uint32*)calloc(BB_PER_SLOT_INTS, 4)))
+ out_of_memory("bitbag_set_bit");
+ }
+
+ bb->bits[slot][ndx/32] |= 1u << (ndx % 32);
+}
+
+#if 0 /* not needed yet */
+void bitbag_clear_bit(struct bitbag *bb, int ndx)
+{
+ int slot = ndx / BB_PER_SLOT_BITS;
+ ndx %= BB_PER_SLOT_BITS;
+
+ if (!bb->bits[slot])
+ return;
+
+ bb->bits[slot][ndx/32] &= ~(1u << (ndx % 32));
+}
+
+int bitbag_check_bit(struct bitbag *bb, int ndx)
+{
+ int slot = ndx / BB_PER_SLOT_BITS;
+ ndx %= BB_PER_SLOT_BITS;
+
+ if (!bb->bits[slot])
+ return 0;
+
+ return bb->bits[slot][ndx/32] & (1u << (ndx % 32)) ? 1 : 0;
+}
+#endif
+
+/* Call this with -1 to start checking from 0. Returns -1 at the end. */
+int bitbag_next_bit(struct bitbag *bb, int after)
+{
+ uint32 bits, mask;
+ int i, ndx = after + 1;
+ int slot = ndx / BB_PER_SLOT_BITS;
+ ndx %= BB_PER_SLOT_BITS;
+
+ mask = (1u << (ndx % 32)) - 1;
+ for (i = ndx / 32; slot < bb->slot_cnt; slot++, i = mask = 0) {
+ if (!bb->bits[slot])
+ continue;
+ for ( ; i < BB_PER_SLOT_INTS; i++, mask = 0) {
+ if (!(bits = bb->bits[slot][i] & ~mask))
+ continue;
+ /* The xor magic figures out the lowest enabled bit in
+ * bits, and the switch quickly computes log2(bit). */
+ switch (bits ^ (bits & (bits-1))) {
+#define LOG2(n) case 1u << n: return slot*BB_PER_SLOT_BITS + i*32 + n
+ LOG2(0); LOG2(1); LOG2(2); LOG2(3);
+ LOG2(4); LOG2(5); LOG2(6); LOG2(7);
+ LOG2(8); LOG2(9); LOG2(10); LOG2(11);
+ LOG2(12); LOG2(13); LOG2(14); LOG2(15);
+ LOG2(16); LOG2(17); LOG2(18); LOG2(19);
+ LOG2(20); LOG2(21); LOG2(22); LOG2(23);
+ LOG2(24); LOG2(25); LOG2(26); LOG2(27);
+ LOG2(28); LOG2(29); LOG2(30); LOG2(31);
+ }
+ return -1; /* impossible... */
+ }
+ }
+
+ return -1;
+}