ewah/ewah_bitmap.c - jrn/git - Git at Google

 /**
  * Copyright 2013, GitHub, Inc
  * Copyright 2009-2013, Daniel Lemire, Cliff Moon,
  *	David McIntosh, Robert Becho, Google Inc. and Veronika Zenz
  *
  * This program 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
  * of the License, or (at your option) any later version.
  *
  * This program 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; if not, see <http://www.gnu.org/licenses/>.
  */
 #include "git-compat-util.h"
 #include "ewok.h"
 #include "ewok_rlw.h"

 static inline size_t min_size(size_t a, size_t b)
 {
 	return a < b ? a : b;
 }

 static inline size_t max_size(size_t a, size_t b)
 {
 	return a > b ? a : b;
 }

 static inline void buffer_grow(struct ewah_bitmap *self, size_t new_size)
 {
 	size_t rlw_offset = (uint8_t *)self->rlw - (uint8_t *)self->buffer;
 	ALLOC_GROW(self->buffer, new_size, self->alloc_size);
 	self->rlw = self->buffer + (rlw_offset / sizeof(eword_t));
 }

 static inline void buffer_push(struct ewah_bitmap *self, eword_t value)
 {
 	buffer_grow(self, self->buffer_size + 1);
 	self->buffer[self->buffer_size++] = value;
 }

 static void buffer_push_rlw(struct ewah_bitmap *self, eword_t value)
 {
 	buffer_push(self, value);
 	self->rlw = self->buffer + self->buffer_size - 1;
 }

 static size_t add_empty_words(struct ewah_bitmap *self, int v, size_t number)
 {
 	size_t added = 0;
 	eword_t runlen, can_add;

 	if (rlw_get_run_bit(self->rlw) != v && rlw_size(self->rlw) == 0) {
 		rlw_set_run_bit(self->rlw, v);
 	} else if (rlw_get_literal_words(self->rlw) != 0 ||
 			rlw_get_run_bit(self->rlw) != v) {
 		buffer_push_rlw(self, 0);
 		if (v) rlw_set_run_bit(self->rlw, v);
 		added++;
 	}

 	runlen = rlw_get_running_len(self->rlw);
 	can_add = min_size(number, RLW_LARGEST_RUNNING_COUNT - runlen);

 	rlw_set_running_len(self->rlw, runlen + can_add);
 	number -= can_add;

 	while (number >= RLW_LARGEST_RUNNING_COUNT) {
 		buffer_push_rlw(self, 0);
 		added++;
 		if (v) rlw_set_run_bit(self->rlw, v);
 		rlw_set_running_len(self->rlw, RLW_LARGEST_RUNNING_COUNT);
 		number -= RLW_LARGEST_RUNNING_COUNT;
 	}

 	if (number > 0) {
 		buffer_push_rlw(self, 0);
 		added++;

 		if (v) rlw_set_run_bit(self->rlw, v);
 		rlw_set_running_len(self->rlw, number);
 	}

 	return added;
 }

 size_t ewah_add_empty_words(struct ewah_bitmap *self, int v, size_t number)
 {
 	if (number == 0)
 		return 0;

 	self->bit_size += number * BITS_IN_EWORD;
 	return add_empty_words(self, v, number);
 }

 static size_t add_literal(struct ewah_bitmap *self, eword_t new_data)
 {
 	eword_t current_num = rlw_get_literal_words(self->rlw);

 	if (current_num >= RLW_LARGEST_LITERAL_COUNT) {
 		buffer_push_rlw(self, 0);

 		rlw_set_literal_words(self->rlw, 1);
 		buffer_push(self, new_data);
 		return 2;
 	}

 	rlw_set_literal_words(self->rlw, current_num + 1);

 	/* sanity check */
 	assert(rlw_get_literal_words(self->rlw) == current_num + 1);

 	buffer_push(self, new_data);
 	return 1;
 }

 void ewah_add_dirty_words(
 	struct ewah_bitmap *self, const eword_t *buffer,
 	size_t number, int negate)
 {
 	size_t literals, can_add;

 	while (1) {
 		literals = rlw_get_literal_words(self->rlw);
 		can_add = min_size(number, RLW_LARGEST_LITERAL_COUNT - literals);

 		rlw_set_literal_words(self->rlw, literals + can_add);

 		buffer_grow(self, self->buffer_size + can_add);

 		if (negate) {
 			size_t i;
 			for (i = 0; i < can_add; ++i)
 				self->buffer[self->buffer_size++] = ~buffer[i];
 		} else {
 			memcpy(self->buffer + self->buffer_size,
 				buffer, can_add * sizeof(eword_t));
 			self->buffer_size += can_add;
 		}

 		self->bit_size += can_add * BITS_IN_EWORD;

 		if (number - can_add == 0)
 			break;

 		buffer_push_rlw(self, 0);
 		buffer += can_add;
 		number -= can_add;
 	}
 }

 static size_t add_empty_word(struct ewah_bitmap *self, int v)
 {
 	int no_literal = (rlw_get_literal_words(self->rlw) == 0);
 	eword_t run_len = rlw_get_running_len(self->rlw);

 	if (no_literal && run_len == 0) {
 		rlw_set_run_bit(self->rlw, v);
 		assert(rlw_get_run_bit(self->rlw) == v);
 	}

 	if (no_literal && rlw_get_run_bit(self->rlw) == v &&
 		run_len < RLW_LARGEST_RUNNING_COUNT) {
 		rlw_set_running_len(self->rlw, run_len + 1);
 		assert(rlw_get_running_len(self->rlw) == run_len + 1);
 		return 0;
 	} else {
 		buffer_push_rlw(self, 0);

 		assert(rlw_get_running_len(self->rlw) == 0);
 		assert(rlw_get_run_bit(self->rlw) == 0);
 		assert(rlw_get_literal_words(self->rlw) == 0);

 		rlw_set_run_bit(self->rlw, v);
 		assert(rlw_get_run_bit(self->rlw) == v);

 		rlw_set_running_len(self->rlw, 1);
 		assert(rlw_get_running_len(self->rlw) == 1);
 		assert(rlw_get_literal_words(self->rlw) == 0);
 		return 1;
 	}
 }

 size_t ewah_add(struct ewah_bitmap *self, eword_t word)
 {
 	self->bit_size += BITS_IN_EWORD;

 	if (word == 0)
 		return add_empty_word(self, 0);

 	if (word == (eword_t)(~0))
 		return add_empty_word(self, 1);

 	return add_literal(self, word);
 }

 void ewah_set(struct ewah_bitmap *self, size_t i)
 {
 	const size_t dist =
 		DIV_ROUND_UP(i + 1, BITS_IN_EWORD) -
 		DIV_ROUND_UP(self->bit_size, BITS_IN_EWORD);

 	assert(i >= self->bit_size);

 	self->bit_size = i + 1;

 	if (dist > 0) {
 		if (dist > 1)
 			add_empty_words(self, 0, dist - 1);

 		add_literal(self, (eword_t)1 << (i % BITS_IN_EWORD));
 		return;
 	}

 	if (rlw_get_literal_words(self->rlw) == 0) {
 		rlw_set_running_len(self->rlw,
 			rlw_get_running_len(self->rlw) - 1);
 		add_literal(self, (eword_t)1 << (i % BITS_IN_EWORD));
 		return;
 	}

 	self->buffer[self->buffer_size - 1] |=
 		((eword_t)1 << (i % BITS_IN_EWORD));

 	/* check if we just completed a stream of 1s */
 	if (self->buffer[self->buffer_size - 1] == (eword_t)(~0)) {
 		self->buffer[--self->buffer_size] = 0;
 		rlw_set_literal_words(self->rlw,
 			rlw_get_literal_words(self->rlw) - 1);
 		add_empty_word(self, 1);
 	}
 }

 void ewah_each_bit(struct ewah_bitmap *self, void (*callback)(size_t, void*), void *payload)
 {
 	size_t pos = 0;
 	size_t pointer = 0;
 	size_t k;

 	while (pointer < self->buffer_size) {
 		eword_t *word = &self->buffer[pointer];

 		if (rlw_get_run_bit(word)) {
 			size_t len = rlw_get_running_len(word) * BITS_IN_EWORD;
 			for (k = 0; k < len; ++k, ++pos)
 				callback(pos, payload);
 		} else {
 			pos += rlw_get_running_len(word) * BITS_IN_EWORD;
 		}

 		++pointer;

 		for (k = 0; k < rlw_get_literal_words(word); ++k) {
 			int c;

 			/* todo: zero count optimization */
 			for (c = 0; c < BITS_IN_EWORD; ++c, ++pos) {
 				if ((self->buffer[pointer] & ((eword_t)1 << c)) != 0)
 					callback(pos, payload);
 			}

 			++pointer;
 		}
 	}
 }

 /**
  * Clear all the bits in the bitmap. Does not free or resize
  * memory.
  */
 static void ewah_clear(struct ewah_bitmap *self)
 {
 	self->buffer_size = 1;
 	self->buffer[0] = 0;
 	self->bit_size = 0;
 	self->rlw = self->buffer;
 }

 struct ewah_bitmap *ewah_new(void)
 {
 	struct ewah_bitmap *self;

 	self = xmalloc(sizeof(struct ewah_bitmap));
 	self->alloc_size = 32;
 	ALLOC_ARRAY(self->buffer, self->alloc_size);

 	ewah_clear(self);
 	return self;
 }

 void ewah_free(struct ewah_bitmap *self)
 {
 	if (!self)
 		return;

 	if (self->alloc_size)
 		free(self->buffer);

 	free(self);
 }

 static void read_new_rlw(struct ewah_iterator *it)
 {
 	const eword_t *word = NULL;

 	it->literals = 0;
 	it->compressed = 0;

 	while (1) {
 		word = &it->buffer[it->pointer];

 		it->rl = rlw_get_running_len(word);
 		it->lw = rlw_get_literal_words(word);
 		it->b = rlw_get_run_bit(word);

 		if (it->rl || it->lw)
 			return;

 		if (it->pointer < it->buffer_size - 1) {
 			it->pointer++;
 		} else {
 			it->pointer = it->buffer_size;
 			return;
 		}
 	}
 }

 int ewah_iterator_next(eword_t *next, struct ewah_iterator *it)
 {
 	if (it->pointer >= it->buffer_size)
 		return 0;

 	if (it->compressed < it->rl) {
 		it->compressed++;
 		*next = it->b ? (eword_t)(~0) : 0;
 	} else {
 		assert(it->literals < it->lw);

 		it->literals++;
 		it->pointer++;

 		assert(it->pointer < it->buffer_size);

 		*next = it->buffer[it->pointer];
 	}

 	if (it->compressed == it->rl && it->literals == it->lw) {
 		if (++it->pointer < it->buffer_size)
 			read_new_rlw(it);
 	}

 	return 1;
 }

 void ewah_iterator_init(struct ewah_iterator *it, struct ewah_bitmap *parent)
 {
 	it->buffer = parent->buffer;
 	it->buffer_size = parent->buffer_size;
 	it->pointer = 0;

 	it->lw = 0;
 	it->rl = 0;
 	it->compressed = 0;
 	it->literals = 0;
 	it->b = 0;

 	if (it->pointer < it->buffer_size)
 		read_new_rlw(it);
 }

 void ewah_xor(
 	struct ewah_bitmap *ewah_i,
 	struct ewah_bitmap *ewah_j,
 	struct ewah_bitmap *out)
 {
 	struct rlw_iterator rlw_i;
 	struct rlw_iterator rlw_j;
 	size_t literals;

 	rlwit_init(&rlw_i, ewah_i);
 	rlwit_init(&rlw_j, ewah_j);

 	while (rlwit_word_size(&rlw_i) > 0 && rlwit_word_size(&rlw_j) > 0) {
 		while (rlw_i.rlw.running_len > 0 || rlw_j.rlw.running_len > 0) {
 			struct rlw_iterator *prey, *predator;
 			size_t index;
 			int negate_words;

 			if (rlw_i.rlw.running_len < rlw_j.rlw.running_len) {
 				prey = &rlw_i;
 				predator = &rlw_j;
 			} else {
 				prey = &rlw_j;
 				predator = &rlw_i;
 			}

 			negate_words = !!predator->rlw.running_bit;
 			index = rlwit_discharge(prey, out,
 				predator->rlw.running_len, negate_words);

 			ewah_add_empty_words(out, negate_words,
 				predator->rlw.running_len - index);

 			rlwit_discard_first_words(predator,
 				predator->rlw.running_len);
 		}

 		literals = min_size(
 			rlw_i.rlw.literal_words,
 			rlw_j.rlw.literal_words);

 		if (literals) {
 			size_t k;

 			for (k = 0; k < literals; ++k) {
 				ewah_add(out,
 					rlw_i.buffer[rlw_i.literal_word_start + k] ^
 					rlw_j.buffer[rlw_j.literal_word_start + k]
 				);
 			}

 			rlwit_discard_first_words(&rlw_i, literals);
 			rlwit_discard_first_words(&rlw_j, literals);
 		}
 	}

 	if (rlwit_word_size(&rlw_i) > 0)
 		rlwit_discharge(&rlw_i, out, ~0, 0);
 	else
 		rlwit_discharge(&rlw_j, out, ~0, 0);

 	out->bit_size = max_size(ewah_i->bit_size, ewah_j->bit_size);
 }

 #define BITMAP_POOL_MAX 16
 static struct ewah_bitmap *bitmap_pool[BITMAP_POOL_MAX];
 static size_t bitmap_pool_size;

 struct ewah_bitmap *ewah_pool_new(void)
 {
 	if (bitmap_pool_size)
 		return bitmap_pool[--bitmap_pool_size];

 	return ewah_new();
 }

 void ewah_pool_free(struct ewah_bitmap *self)
 {
 	if (!self)
 		return;

 	if (bitmap_pool_size == BITMAP_POOL_MAX ||
 		self->alloc_size == 0) {
 		ewah_free(self);
 		return;
 	}

 	ewah_clear(self);
 	bitmap_pool[bitmap_pool_size++] = self;
 }

 uint32_t ewah_checksum(struct ewah_bitmap *self)
 {
 	const uint8_t *p = (uint8_t *)self->buffer;
 	uint32_t crc = (uint32_t)self->bit_size;
 	size_t size = self->buffer_size * sizeof(eword_t);

 	while (size--)
 		crc = (crc << 5) - crc + (uint32_t)*p++;

 	return crc;
 }
	/**
	* Copyright 2013, GitHub, Inc
	* Copyright 2009-2013, Daniel Lemire, Cliff Moon,
	* David McIntosh, Robert Becho, Google Inc. and Veronika Zenz
	*
	* This program 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
	* of the License, or (at your option) any later version.
	*
	* This program 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; if not, see <http://www.gnu.org/licenses/>.
	*/
	#include "git-compat-util.h"
	#include "ewok.h"
	#include "ewok_rlw.h"

	static inline size_t min_size(size_t a, size_t b)
	{
	return a < b ? a : b;
	}

	static inline size_t max_size(size_t a, size_t b)
	{
	return a > b ? a : b;
	}

	static inline void buffer_grow(struct ewah_bitmap *self, size_t new_size)
	{
	size_t rlw_offset = (uint8_t )self->rlw - (uint8_t )self->buffer;
	ALLOC_GROW(self->buffer, new_size, self->alloc_size);
	self->rlw = self->buffer + (rlw_offset / sizeof(eword_t));
	}

	static inline void buffer_push(struct ewah_bitmap *self, eword_t value)
	{
	buffer_grow(self, self->buffer_size + 1);
	self->buffer[self->buffer_size++] = value;
	}

	static void buffer_push_rlw(struct ewah_bitmap *self, eword_t value)
	{
	buffer_push(self, value);
	self->rlw = self->buffer + self->buffer_size - 1;
	}

	static size_t add_empty_words(struct ewah_bitmap *self, int v, size_t number)
	{
	size_t added = 0;
	eword_t runlen, can_add;

	if (rlw_get_run_bit(self->rlw) != v && rlw_size(self->rlw) == 0) {
	rlw_set_run_bit(self->rlw, v);
	} else if (rlw_get_literal_words(self->rlw) != 0 \|\|
	rlw_get_run_bit(self->rlw) != v) {
	buffer_push_rlw(self, 0);
	if (v) rlw_set_run_bit(self->rlw, v);
	added++;
	}

	runlen = rlw_get_running_len(self->rlw);
	can_add = min_size(number, RLW_LARGEST_RUNNING_COUNT - runlen);

	rlw_set_running_len(self->rlw, runlen + can_add);
	number -= can_add;

	while (number >= RLW_LARGEST_RUNNING_COUNT) {
	buffer_push_rlw(self, 0);
	added++;
	if (v) rlw_set_run_bit(self->rlw, v);
	rlw_set_running_len(self->rlw, RLW_LARGEST_RUNNING_COUNT);
	number -= RLW_LARGEST_RUNNING_COUNT;
	}

	if (number > 0) {
	buffer_push_rlw(self, 0);
	added++;

	if (v) rlw_set_run_bit(self->rlw, v);
	rlw_set_running_len(self->rlw, number);
	}

	return added;
	}

	size_t ewah_add_empty_words(struct ewah_bitmap *self, int v, size_t number)
	{
	if (number == 0)
	return 0;

	self->bit_size += number * BITS_IN_EWORD;
	return add_empty_words(self, v, number);
	}

	static size_t add_literal(struct ewah_bitmap *self, eword_t new_data)
	{
	eword_t current_num = rlw_get_literal_words(self->rlw);

	if (current_num >= RLW_LARGEST_LITERAL_COUNT) {
	buffer_push_rlw(self, 0);

	rlw_set_literal_words(self->rlw, 1);
	buffer_push(self, new_data);
	return 2;
	}

	rlw_set_literal_words(self->rlw, current_num + 1);

	/* sanity check */
	assert(rlw_get_literal_words(self->rlw) == current_num + 1);

	buffer_push(self, new_data);
	return 1;
	}

	void ewah_add_dirty_words(
	struct ewah_bitmap self, const eword_t buffer,
	size_t number, int negate)
	{
	size_t literals, can_add;

	while (1) {
	literals = rlw_get_literal_words(self->rlw);
	can_add = min_size(number, RLW_LARGEST_LITERAL_COUNT - literals);

	rlw_set_literal_words(self->rlw, literals + can_add);

	buffer_grow(self, self->buffer_size + can_add);

	if (negate) {
	size_t i;
	for (i = 0; i < can_add; ++i)
	self->buffer[self->buffer_size++] = ~buffer[i];
	} else {
	memcpy(self->buffer + self->buffer_size,
	buffer, can_add * sizeof(eword_t));
	self->buffer_size += can_add;
	}

	self->bit_size += can_add * BITS_IN_EWORD;

	if (number - can_add == 0)
	break;

	buffer_push_rlw(self, 0);
	buffer += can_add;
	number -= can_add;
	}
	}

	static size_t add_empty_word(struct ewah_bitmap *self, int v)
	{
	int no_literal = (rlw_get_literal_words(self->rlw) == 0);
	eword_t run_len = rlw_get_running_len(self->rlw);

	if (no_literal && run_len == 0) {
	rlw_set_run_bit(self->rlw, v);
	assert(rlw_get_run_bit(self->rlw) == v);
	}

	if (no_literal && rlw_get_run_bit(self->rlw) == v &&
	run_len < RLW_LARGEST_RUNNING_COUNT) {
	rlw_set_running_len(self->rlw, run_len + 1);
	assert(rlw_get_running_len(self->rlw) == run_len + 1);
	return 0;
	} else {
	buffer_push_rlw(self, 0);

	assert(rlw_get_running_len(self->rlw) == 0);
	assert(rlw_get_run_bit(self->rlw) == 0);
	assert(rlw_get_literal_words(self->rlw) == 0);

	rlw_set_run_bit(self->rlw, v);
	assert(rlw_get_run_bit(self->rlw) == v);

	rlw_set_running_len(self->rlw, 1);
	assert(rlw_get_running_len(self->rlw) == 1);
	assert(rlw_get_literal_words(self->rlw) == 0);
	return 1;
	}
	}

	size_t ewah_add(struct ewah_bitmap *self, eword_t word)
	{
	self->bit_size += BITS_IN_EWORD;

	if (word == 0)
	return add_empty_word(self, 0);

	if (word == (eword_t)(~0))
	return add_empty_word(self, 1);

	return add_literal(self, word);
	}

	void ewah_set(struct ewah_bitmap *self, size_t i)
	{
	const size_t dist =
	DIV_ROUND_UP(i + 1, BITS_IN_EWORD) -
	DIV_ROUND_UP(self->bit_size, BITS_IN_EWORD);

	assert(i >= self->bit_size);

	self->bit_size = i + 1;

	if (dist > 0) {
	if (dist > 1)
	add_empty_words(self, 0, dist - 1);

	add_literal(self, (eword_t)1 << (i % BITS_IN_EWORD));
	return;
	}

	if (rlw_get_literal_words(self->rlw) == 0) {
	rlw_set_running_len(self->rlw,
	rlw_get_running_len(self->rlw) - 1);
	add_literal(self, (eword_t)1 << (i % BITS_IN_EWORD));
	return;
	}

	self->buffer[self->buffer_size - 1] \|=
	((eword_t)1 << (i % BITS_IN_EWORD));

	/* check if we just completed a stream of 1s */
	if (self->buffer[self->buffer_size - 1] == (eword_t)(~0)) {
	self->buffer[--self->buffer_size] = 0;
	rlw_set_literal_words(self->rlw,
	rlw_get_literal_words(self->rlw) - 1);
	add_empty_word(self, 1);
	}
	}

	void ewah_each_bit(struct ewah_bitmap self, void (callback)(size_t, void), void payload)
	{
	size_t pos = 0;
	size_t pointer = 0;
	size_t k;

	while (pointer < self->buffer_size) {
	eword_t *word = &self->buffer[pointer];

	if (rlw_get_run_bit(word)) {
	size_t len = rlw_get_running_len(word) * BITS_IN_EWORD;
	for (k = 0; k < len; ++k, ++pos)
	callback(pos, payload);
	} else {
	pos += rlw_get_running_len(word) * BITS_IN_EWORD;
	}

	++pointer;

	for (k = 0; k < rlw_get_literal_words(word); ++k) {
	int c;

	/* todo: zero count optimization */
	for (c = 0; c < BITS_IN_EWORD; ++c, ++pos) {
	if ((self->buffer[pointer] & ((eword_t)1 << c)) != 0)
	callback(pos, payload);
	}

	++pointer;
	}
	}
	}

	/**
	* Clear all the bits in the bitmap. Does not free or resize
	* memory.
	*/
	static void ewah_clear(struct ewah_bitmap *self)
	{
	self->buffer_size = 1;
	self->buffer[0] = 0;
	self->bit_size = 0;
	self->rlw = self->buffer;
	}

	struct ewah_bitmap *ewah_new(void)
	{
	struct ewah_bitmap *self;

	self = xmalloc(sizeof(struct ewah_bitmap));
	self->alloc_size = 32;
	ALLOC_ARRAY(self->buffer, self->alloc_size);

	ewah_clear(self);
	return self;
	}

	void ewah_free(struct ewah_bitmap *self)
	{
	if (!self)
	return;

	if (self->alloc_size)
	free(self->buffer);

	free(self);
	}

	static void read_new_rlw(struct ewah_iterator *it)
	{
	const eword_t *word = NULL;

	it->literals = 0;
	it->compressed = 0;

	while (1) {
	word = &it->buffer[it->pointer];

	it->rl = rlw_get_running_len(word);
	it->lw = rlw_get_literal_words(word);
	it->b = rlw_get_run_bit(word);

	if (it->rl \|\| it->lw)
	return;

	if (it->pointer < it->buffer_size - 1) {
	it->pointer++;
	} else {
	it->pointer = it->buffer_size;
	return;
	}
	}
	}

	int ewah_iterator_next(eword_t next, struct ewah_iterator it)
	{
	if (it->pointer >= it->buffer_size)
	return 0;

	if (it->compressed < it->rl) {
	it->compressed++;
	*next = it->b ? (eword_t)(~0) : 0;
	} else {
	assert(it->literals < it->lw);

	it->literals++;
	it->pointer++;

	assert(it->pointer < it->buffer_size);

	*next = it->buffer[it->pointer];
	}

	if (it->compressed == it->rl && it->literals == it->lw) {
	if (++it->pointer < it->buffer_size)
	read_new_rlw(it);
	}

	return 1;
	}

	void ewah_iterator_init(struct ewah_iterator it, struct ewah_bitmap parent)
	{
	it->buffer = parent->buffer;
	it->buffer_size = parent->buffer_size;
	it->pointer = 0;

	it->lw = 0;
	it->rl = 0;
	it->compressed = 0;
	it->literals = 0;
	it->b = 0;

	if (it->pointer < it->buffer_size)
	read_new_rlw(it);
	}

	void ewah_xor(
	struct ewah_bitmap *ewah_i,
	struct ewah_bitmap *ewah_j,
	struct ewah_bitmap *out)
	{
	struct rlw_iterator rlw_i;
	struct rlw_iterator rlw_j;
	size_t literals;

	rlwit_init(&rlw_i, ewah_i);
	rlwit_init(&rlw_j, ewah_j);

	while (rlwit_word_size(&rlw_i) > 0 && rlwit_word_size(&rlw_j) > 0) {
	while (rlw_i.rlw.running_len > 0 \|\| rlw_j.rlw.running_len > 0) {
	struct rlw_iterator prey, predator;
	size_t index;
	int negate_words;

	if (rlw_i.rlw.running_len < rlw_j.rlw.running_len) {
	prey = &rlw_i;
	predator = &rlw_j;
	} else {
	prey = &rlw_j;
	predator = &rlw_i;
	}

	negate_words = !!predator->rlw.running_bit;
	index = rlwit_discharge(prey, out,
	predator->rlw.running_len, negate_words);

	ewah_add_empty_words(out, negate_words,
	predator->rlw.running_len - index);

	rlwit_discard_first_words(predator,
	predator->rlw.running_len);
	}

	literals = min_size(
	rlw_i.rlw.literal_words,
	rlw_j.rlw.literal_words);

	if (literals) {
	size_t k;

	for (k = 0; k < literals; ++k) {
	ewah_add(out,
	rlw_i.buffer[rlw_i.literal_word_start + k] ^
	rlw_j.buffer[rlw_j.literal_word_start + k]
	);
	}

	rlwit_discard_first_words(&rlw_i, literals);
	rlwit_discard_first_words(&rlw_j, literals);
	}
	}

	if (rlwit_word_size(&rlw_i) > 0)
	rlwit_discharge(&rlw_i, out, ~0, 0);
	else
	rlwit_discharge(&rlw_j, out, ~0, 0);

	out->bit_size = max_size(ewah_i->bit_size, ewah_j->bit_size);
	}

	#define BITMAP_POOL_MAX 16
	static struct ewah_bitmap *bitmap_pool[BITMAP_POOL_MAX];
	static size_t bitmap_pool_size;

	struct ewah_bitmap *ewah_pool_new(void)
	{
	if (bitmap_pool_size)
	return bitmap_pool[--bitmap_pool_size];

	return ewah_new();
	}

	void ewah_pool_free(struct ewah_bitmap *self)
	{
	if (!self)
	return;

	if (bitmap_pool_size == BITMAP_POOL_MAX \|\|
	self->alloc_size == 0) {
	ewah_free(self);
	return;
	}

	ewah_clear(self);
	bitmap_pool[bitmap_pool_size++] = self;
	}

	uint32_t ewah_checksum(struct ewah_bitmap *self)
	{
	const uint8_t p = (uint8_t )self->buffer;
	uint32_t crc = (uint32_t)self->bit_size;
	size_t size = self->buffer_size * sizeof(eword_t);

	while (size--)
	crc = (crc << 5) - crc + (uint32_t)*p++;

	return crc;
	}