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+/* Bitfields
+ * Copyright (C) 2016 Cumulus Networks, Inc.
+ *
+ * This file is part of Quagga.
+ *
+ * Quagga is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2, or (at your option) any
+ * later version.
+ *
+ * Quagga 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 General Public License along
+ * with this program; see the file COPYING; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+/**
+ * A simple bit array implementation to allocate and free IDs. An example
+ * of its usage is in allocating link state IDs for OSPFv3 as OSPFv3 has
+ * removed all address semantics from LS ID. Another usage can be in
+ * allocating IDs for BGP neighbors (and dynamic update groups) for
+ * efficient storage of adj-rib-out.
+ *
+ * An example:
+ * #include "bitfield.h"
+ *
+ * bitfield_t bitfield;
+ *
+ * bf_init(bitfield, 32);
+ * ...
+ * bf_assign_index(bitfield, id1);
+ * bf_assign_index(bitfield, id2);
+ * ...
+ * bf_release_index(bitfield, id1);
+ */
+
+#ifndef _BITFIELD_H
+#define _BITFIELD_H
+
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef unsigned int word_t;
+#define WORD_MAX 0xFFFFFFFF
+#define WORD_SIZE (sizeof(word_t) * 8)
+
+/**
+ * The bitfield structure.
+ * @data: the bits to manage.
+ * @n: The current word number that is being used.
+ * @m: total number of words in 'data'
+ */
+typedef struct {word_t *data; size_t n, m; } bitfield_t;
+
+DECLARE_MTYPE(BITFIELD);
+
+/**
+ * Initialize the bits.
+ * @v: an instance of bitfield_t struct.
+ * @N: number of bits to start with, which equates to how many
+ * IDs can be allocated.
+ */
+#define bf_init(v, N) \
+ do { \
+ (v).n = 0; \
+ (v).m = ((N) / WORD_SIZE + 1); \
+ (v).data = XCALLOC(MTYPE_BITFIELD, ((v).m * sizeof(word_t))); \
+ } while (0)
+
+/**
+ * allocate and assign an id from bitfield v.
+ */
+#define bf_assign_index(v, id) \
+ do { \
+ bf_find_bit(v, id); \
+ bf_set_bit(v, id); \
+ } while (0)
+
+/*
+ * allocate and assign 0th bit in the bitfiled.
+ */
+#define bf_assign_zero_index(v) \
+ do { \
+ int id = 0; \
+ bf_assign_index(v, id); \
+ } while (0)
+
+/*
+ * return an id to bitfield v
+ */
+#define bf_release_index(v, id) \
+ (v).data[bf_index(id)] &= ~(1 << (bf_offset(id)))
+
+/* check if an id is in use */
+#define bf_test_index(v, id) \
+ ((v).data[bf_index(id)] & (1 << (bf_offset(id))))
+
+/* check if the bit field has been setup */
+#define bf_is_inited(v) ((v).data)
+
+/* compare two bitmaps of the same length */
+#define bf_cmp(v1, v2) (memcmp((v1).data, (v2).data, ((v1).m * sizeof(word_t))))
+
+/*
+ * return 0th index back to bitfield
+ */
+#define bf_release_zero_index(v) bf_release_index(v, 0)
+
+#define bf_index(b) ((b) / WORD_SIZE)
+#define bf_offset(b) ((b) % WORD_SIZE)
+
+/**
+ * Set a bit in the array. If it fills up that word and we are
+ * out of words, extend it by one more word.
+ */
+#define bf_set_bit(v, b) \
+ do { \
+ size_t w = bf_index(b); \
+ (v).data[w] |= 1 << (bf_offset(b)); \
+ (v).n += ((v).data[w] == WORD_MAX); \
+ if ((v).n == (v).m) { \
+ (v).m = (v).m + 1; \
+ (v).data = realloc((v).data, (v).m * sizeof(word_t)); \
+ } \
+ } while (0)
+
+/* Find a clear bit in v and assign it to b. */
+#define bf_find_bit(v, b) \
+ do { \
+ word_t word = 0; \
+ unsigned int w, sh; \
+ for (w = 0; w <= (v).n; w++) { \
+ if ((word = (v).data[w]) != WORD_MAX) \
+ break; \
+ } \
+ (b) = ((word & 0xFFFF) == 0xFFFF) << 4; \
+ word >>= (b); \
+ sh = ((word & 0xFF) == 0xFF) << 3; \
+ word >>= sh; \
+ (b) |= sh; \
+ sh = ((word & 0xF) == 0xF) << 2; \
+ word >>= sh; \
+ (b) |= sh; \
+ sh = ((word & 0x3) == 0x3) << 1; \
+ word >>= sh; \
+ (b) |= sh; \
+ sh = ((word & 0x1) == 0x1) << 0; \
+ word >>= sh; \
+ (b) |= sh; \
+ (b) += (w * WORD_SIZE); \
+ } while (0)
+
+/*
+ * Find a clear bit in v and return it
+ * Start looking in the word containing bit position start_index.
+ * If necessary, wrap around after bit position max_index.
+ */
+static inline unsigned int
+bf_find_next_clear_bit_wrap(bitfield_t *v, word_t start_index, word_t max_index)
+{
+ int start_bit;
+ unsigned long i, offset, scanbits, wordcount_max, index_max;
+
+ if (start_index > max_index)
+ start_index = 0;
+
+ start_bit = start_index & (WORD_SIZE - 1);
+ wordcount_max = bf_index(max_index) + 1;
+
+ scanbits = WORD_SIZE;
+ for (i = bf_index(start_index); i < v->m; ++i) {
+ if (v->data[i] == WORD_MAX) {
+ /* if the whole word is full move to the next */
+ start_bit = 0;
+ continue;
+ }
+ /* scan one word for clear bits */
+ if ((i == v->m - 1) && (v->m >= wordcount_max))
+ /* max index could be only part of word */
+ scanbits = (max_index % WORD_SIZE) + 1;
+ for (offset = start_bit; offset < scanbits; ++offset) {
+ if (!((v->data[i] >> offset) & 1))
+ return ((i * WORD_SIZE) + offset);
+ }
+ /* move to the next word */
+ start_bit = 0;
+ }
+
+ if (v->m < wordcount_max) {
+ /*
+ * We can expand bitfield, so no need to wrap.
+ * Return the index of the first bit of the next word.
+ * Assumption is that caller will call bf_set_bit which
+ * will allocate additional space.
+ */
+ v->m += 1;
+ v->data = (word_t *)realloc(v->data, v->m * sizeof(word_t));
+ v->data[v->m - 1] = 0;
+ return v->m * WORD_SIZE;
+ }
+
+ /*
+ * start looking for a clear bit at the start of the bitfield and
+ * stop when we reach start_index
+ */
+ scanbits = WORD_SIZE;
+ index_max = bf_index(start_index - 1);
+ for (i = 0; i <= index_max; ++i) {
+ if (i == index_max)
+ scanbits = ((start_index - 1) % WORD_SIZE) + 1;
+ for (offset = start_bit; offset < scanbits; ++offset) {
+ if (!((v->data[i] >> offset) & 1))
+ return ((i * WORD_SIZE) + offset);
+ }
+ /* move to the next word */
+ start_bit = 0;
+ }
+
+ return WORD_MAX;
+}
+
+static inline unsigned int bf_find_next_set_bit(bitfield_t v,
+ word_t start_index)
+{
+ int start_bit;
+ unsigned long i, offset;
+
+ start_bit = start_index & (WORD_SIZE - 1);
+
+ for (i = bf_index(start_index); i < v.m; ++i) {
+ if (v.data[i] == 0) {
+ /* if the whole word is empty move to the next */
+ start_bit = 0;
+ continue;
+ }
+ /* scan one word for set bits */
+ for (offset = start_bit; offset < WORD_SIZE; ++offset) {
+ if ((v.data[i] >> offset) & 1)
+ return ((i * WORD_SIZE) + offset);
+ }
+ /* move to the next word */
+ start_bit = 0;
+ }
+ return WORD_MAX;
+}
+
+/* iterate through all the set bits */
+#define bf_for_each_set_bit(v, b, max) \
+ for ((b) = bf_find_next_set_bit((v), 0); \
+ (b) < max; \
+ (b) = bf_find_next_set_bit((v), (b) + 1))
+
+/*
+ * Free the allocated memory for data
+ * @v: an instance of bitfield_t struct.
+ */
+#define bf_free(v) \
+ do { \
+ XFREE(MTYPE_BITFIELD, (v).data); \
+ (v).data = NULL; \
+ } while (0)
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
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