[pulseview.git] / pv / data / logicsnapshot.cpp

/*
 * This file is part of the PulseView project.
 *
 * Copyright (C) 2012 Joel Holdsworth <joel@airwebreathe.org.uk>
 *
 * 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, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
 */

#include <extdef.h>

#include <assert.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>

#include "config.h"
#include "logicsnapshot.h"

using std::lock_guard;
using std::recursive_mutex;
using std::max;
using std::min;
using std::pair;

namespace pv {
namespace data {

const int LogicSnapshot::MipMapScalePower = 4;
const int LogicSnapshot::MipMapScaleFactor = 1 << MipMapScalePower;
const float LogicSnapshot::LogMipMapScaleFactor = logf(MipMapScaleFactor);
const uint64_t LogicSnapshot::MipMapDataUnit = 64*1024;	// bytes

LogicSnapshot::LogicSnapshot(const sr_datafeed_logic &logic,
                             const uint64_t expected_num_samples) :
	Snapshot(logic.unitsize),
	_last_append_sample(0)
{
	set_capacity(expected_num_samples);

	lock_guard<recursive_mutex> lock(_mutex);
	memset(_mip_map, 0, sizeof(_mip_map));
	append_payload(logic);
}

LogicSnapshot::~LogicSnapshot()
{
	lock_guard<recursive_mutex> lock(_mutex);
	for (MipMapLevel &l : _mip_map)
		free(l.data);
}

uint64_t LogicSnapshot::unpack_sample(const uint8_t *ptr) const
{
#ifdef HAVE_UNALIGNED_LITTLE_ENDIAN_ACCESS
	return *(uint64_t*)ptr;
#else
	uint64_t value = 0;
	switch(_unit_size) {
	default:
		value |= ((uint64_t)ptr[7]) << 56;
		/* FALLTHRU */
	case 7:
		value |= ((uint64_t)ptr[6]) << 48;
		/* FALLTHRU */
	case 6:
		value |= ((uint64_t)ptr[5]) << 40;
		/* FALLTHRU */
	case 5:
		value |= ((uint64_t)ptr[4]) << 32;
		/* FALLTHRU */
	case 4:
		value |= ((uint32_t)ptr[3]) << 24;
		/* FALLTHRU */
	case 3:
		value |= ((uint32_t)ptr[2]) << 16;
		/* FALLTHRU */
	case 2:
		value |= ptr[1] << 8;
		/* FALLTHRU */
	case 1:
		value |= ptr[0];
		/* FALLTHRU */
	case 0:
		break;
	}
	return value;
#endif
}

void LogicSnapshot::pack_sample(uint8_t *ptr, uint64_t value)
{
#ifdef HAVE_UNALIGNED_LITTLE_ENDIAN_ACCESS
	*(uint64_t*)ptr = value;
#else
	switch(_unit_size) {
	default:
		ptr[7] = value >> 56;
		/* FALLTHRU */
	case 7:
		ptr[6] = value >> 48;
		/* FALLTHRU */
	case 6:
		ptr[5] = value >> 40;
		/* FALLTHRU */
	case 5:
		ptr[4] = value >> 32;
		/* FALLTHRU */
	case 4:
		ptr[3] = value >> 24;
		/* FALLTHRU */
	case 3:
		ptr[2] = value >> 16;
		/* FALLTHRU */
	case 2:
		ptr[1] = value >> 8;
		/* FALLTHRU */
	case 1:
		ptr[0] = value;
		/* FALLTHRU */
	case 0:
		break;
	}
#endif
}

void LogicSnapshot::append_payload(
	const sr_datafeed_logic &logic)
{
	assert(_unit_size == logic.unitsize);
	assert((logic.length % _unit_size) == 0);

	lock_guard<recursive_mutex> lock(_mutex);

	append_data(logic.data, logic.length / _unit_size);

	// Generate the first mip-map from the data
	append_payload_to_mipmap();
}

void LogicSnapshot::get_samples(uint8_t *const data,
	int64_t start_sample, int64_t end_sample) const
{
	assert(data);
	assert(start_sample >= 0);
	assert(start_sample <= (int64_t)_sample_count);
	assert(end_sample >= 0);
	assert(end_sample <= (int64_t)_sample_count);
	assert(start_sample <= end_sample);

	lock_guard<recursive_mutex> lock(_mutex);

	const size_t size = (end_sample - start_sample) * _unit_size;
	memcpy(data, (const uint8_t*)_data + start_sample * _unit_size, size);
}

void LogicSnapshot::reallocate_mipmap_level(MipMapLevel &m)
{
	const uint64_t new_data_length = ((m.length + MipMapDataUnit - 1) /
		MipMapDataUnit) * MipMapDataUnit;
	if (new_data_length > m.data_length)
	{
		m.data_length = new_data_length;

		// Padding is added to allow for the uint64_t write word
		m.data = realloc(m.data, new_data_length * _unit_size +
			sizeof(uint64_t));
	}
}

void LogicSnapshot::append_payload_to_mipmap()
{
	MipMapLevel &m0 = _mip_map[0];
	uint64_t prev_length;
	const uint8_t *src_ptr;
	uint8_t *dest_ptr;
	uint64_t accumulator;
	unsigned int diff_counter;

	// Expand the data buffer to fit the new samples
	prev_length = m0.length;
	m0.length = _sample_count / MipMapScaleFactor;

	// Break off if there are no new samples to compute
	if (m0.length == prev_length)
		return;

	reallocate_mipmap_level(m0);

	dest_ptr = (uint8_t*)m0.data + prev_length * _unit_size;

	// Iterate through the samples to populate the first level mipmap
	const uint8_t *const end_src_ptr = (uint8_t*)_data +
		m0.length * _unit_size * MipMapScaleFactor;
	for (src_ptr = (uint8_t*)_data +
		prev_length * _unit_size * MipMapScaleFactor;
		src_ptr < end_src_ptr;)
	{
		// Accumulate transitions which have occurred in this sample
		accumulator = 0;
		diff_counter = MipMapScaleFactor;
		while (diff_counter-- > 0)
		{
			const uint64_t sample = unpack_sample(src_ptr);
			accumulator |= _last_append_sample ^ sample;
			_last_append_sample = sample;
			src_ptr += _unit_size;
		}

		pack_sample(dest_ptr, accumulator);
		dest_ptr += _unit_size;
	}

	// Compute higher level mipmaps
	for (unsigned int level = 1; level < ScaleStepCount; level++)
	{
		MipMapLevel &m = _mip_map[level];
		const MipMapLevel &ml = _mip_map[level-1];

		// Expand the data buffer to fit the new samples
		prev_length = m.length;
		m.length = ml.length / MipMapScaleFactor;

		// Break off if there are no more samples to computed
		if (m.length == prev_length)
			break;

		reallocate_mipmap_level(m);

		// Subsample the level lower level
		src_ptr = (uint8_t*)ml.data +
			_unit_size * prev_length * MipMapScaleFactor;
		const uint8_t *const end_dest_ptr =
			(uint8_t*)m.data + _unit_size * m.length;
		for (dest_ptr = (uint8_t*)m.data +
			_unit_size * prev_length;
			dest_ptr < end_dest_ptr;
			dest_ptr += _unit_size)
		{
			accumulator = 0;
			diff_counter = MipMapScaleFactor;
			while (diff_counter-- > 0)
			{
				accumulator |= unpack_sample(src_ptr);
				src_ptr += _unit_size;
			}

			pack_sample(dest_ptr, accumulator);
		}
	}
}

uint64_t LogicSnapshot::get_sample(uint64_t index) const
{
	assert(_data);
	assert(index < _sample_count);

	return unpack_sample((uint8_t*)_data + index * _unit_size);
}

void LogicSnapshot::get_subsampled_edges(
	std::vector<EdgePair> &edges,
	uint64_t start, uint64_t end,
	float min_length, int sig_index)
{
	uint64_t index = start;
	unsigned int level;
	bool last_sample;
	bool fast_forward;

	assert(end <= get_sample_count());
	assert(start <= end);
	assert(min_length > 0);
	assert(sig_index >= 0);
	assert(sig_index < 64);

	lock_guard<recursive_mutex> lock(_mutex);

	const uint64_t block_length = (uint64_t)max(min_length, 1.0f);
	const unsigned int min_level = max((int)floorf(logf(min_length) /
		LogMipMapScaleFactor) - 1, 0);
	const uint64_t sig_mask = 1ULL << sig_index;

	// Store the initial state
	last_sample = (get_sample(start) & sig_mask) != 0;
	edges.push_back(pair<int64_t, bool>(index++, last_sample));

	while (index + block_length <= end)
	{
		//----- Continue to search -----//
		level = min_level;

		// We cannot fast-forward if there is no mip-map data at
		// at the minimum level.
		fast_forward = (_mip_map[level].data != NULL);

		if (min_length < MipMapScaleFactor)
		{
			// Search individual samples up to the beginning of
			// the next first level mip map block
			const uint64_t final_index = min(end,
				pow2_ceil(index, MipMapScalePower));

			for (; index < final_index &&
				(index & ~(~0 << MipMapScalePower)) != 0;
				index++)
			{
				const bool sample =
					(get_sample(index) & sig_mask) != 0;

				// If there was a change we cannot fast forward
				if (sample != last_sample) {
					fast_forward = false;
					break;
				}
			}
		}
		else
		{
			// If resolution is less than a mip map block,
			// round up to the beginning of the mip-map block
			// for this level of detail
			const int min_level_scale_power =
				(level + 1) * MipMapScalePower;
			index = pow2_ceil(index, min_level_scale_power);
			if (index >= end)
				break;

			// We can fast forward only if there was no change
			const bool sample =
				(get_sample(index) & sig_mask) != 0;
			if (last_sample != sample)
				fast_forward = false;
		}

		if (fast_forward) {

			// Fast forward: This involves zooming out to higher
			// levels of the mip map searching for changes, then
			// zooming in on them to find the point where the edge
			// begins.

			// Slide right and zoom out at the beginnings of mip-map
			// blocks until we encounter a change
			while (1) {
				const int level_scale_power =
					(level + 1) * MipMapScalePower;
				const uint64_t offset =
					index >> level_scale_power;

				// Check if we reached the last block at this
				// level, or if there was a change in this block
				if (offset >= _mip_map[level].length ||
					(get_subsample(level, offset) &
						sig_mask))
					break;

				if ((offset & ~(~0 << MipMapScalePower)) == 0) {
					// If we are now at the beginning of a
					// higher level mip-map block ascend one
					// level
					if (level + 1 >= ScaleStepCount ||
						!_mip_map[level + 1].data)
						break;

					level++;
				} else {
					// Slide right to the beginning of the
					// next mip map block
					index = pow2_ceil(index + 1,
						level_scale_power);
				}
			}

			// Zoom in, and slide right until we encounter a change,
			// and repeat until we reach min_level
			while (1) {
				assert(_mip_map[level].data);

				const int level_scale_power =
					(level + 1) * MipMapScalePower;
				const uint64_t offset =
					index >> level_scale_power;

				// Check if we reached the last block at this
				// level, or if there was a change in this block
				if (offset >= _mip_map[level].length ||
					(get_subsample(level, offset) &
						sig_mask)) {
					// Zoom in unless we reached the minimum
					// zoom
					if (level == min_level)
						break;

					level--;
				} else {
					// Slide right to the beginning of the
					// next mip map block
					index = pow2_ceil(index + 1,
						level_scale_power);
				}
			}

			// If individual samples within the limit of resolution,
			// do a linear search for the next transition within the
			// block
			if (min_length < MipMapScaleFactor) {
				for (; index < end; index++) {
					const bool sample = (get_sample(index) &
						sig_mask) != 0;
					if (sample != last_sample)
						break;
				}
			}
		}

		//----- Store the edge -----//

		// Take the last sample of the quanization block
		const int64_t final_index = index + block_length;
		if (index + block_length > end)
			break;

		// Store the final state
		const bool final_sample =
			(get_sample(final_index - 1) & sig_mask) != 0;
		edges.push_back(pair<int64_t, bool>(index, final_sample));

		index = final_index;
		last_sample = final_sample;
	}

	// Add the final state
	const bool end_sample = get_sample(end) & sig_mask;
	if (last_sample != end_sample)
		edges.push_back(pair<int64_t, bool>(end, end_sample));
	edges.push_back(pair<int64_t, bool>(end + 1, end_sample));
}

uint64_t LogicSnapshot::get_subsample(int level, uint64_t offset) const
{
	assert(level >= 0);
	assert(_mip_map[level].data);
	return unpack_sample((uint8_t*)_mip_map[level].data +
		_unit_size * offset);
}

uint64_t LogicSnapshot::pow2_ceil(uint64_t x, unsigned int power)
{
	const uint64_t p = 1 << power;
	return (x + p - 1) / p * p;
}

} // namespace data
} // namespace pv
Commit	Line	Data
	1	/*
	2	* This file is part of the PulseView project.
	3	*
	4	* Copyright (C) 2012 Joel Holdsworth <joel@airwebreathe.org.uk>
	5	*
	6	* This program is free software; you can redistribute it and/or modify
	7	* it under the terms of the GNU General Public License as published by
	8	* the Free Software Foundation; either version 2 of the License, or
	9	* (at your option) any later version.
	10	*
	11	* This program is distributed in the hope that it will be useful,
	12	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	13	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	14	* GNU General Public License for more details.
	15	*
	16	* You should have received a copy of the GNU General Public License
	17	* along with this program; if not, write to the Free Software
	18	* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
	19	*/
	20
	21	#include <extdef.h>
	22
	23	#include <assert.h>
	24	#include <string.h>
	25	#include <stdlib.h>
	26	#include <math.h>
	27
	28	#include "config.h"
	29	#include "logicsnapshot.h"
	30
	31	using std::lock_guard;
	32	using std::recursive_mutex;
	33	using std::max;
	34	using std::min;
	35	using std::pair;
	36
	37	namespace pv {
	38	namespace data {
	39
	40	const int LogicSnapshot::MipMapScalePower = 4;
	41	const int LogicSnapshot::MipMapScaleFactor = 1 << MipMapScalePower;
	42	const float LogicSnapshot::LogMipMapScaleFactor = logf(MipMapScaleFactor);
	43	const uint64_t LogicSnapshot::MipMapDataUnit = 64*1024; // bytes
	44
	45	LogicSnapshot::LogicSnapshot(const sr_datafeed_logic &logic,
	46	const uint64_t expected_num_samples) :
	47	Snapshot(logic.unitsize),
	48	_last_append_sample(0)
	49	{
	50	set_capacity(expected_num_samples);
	51
	52	lock_guard<recursive_mutex> lock(_mutex);
	53	memset(_mip_map, 0, sizeof(_mip_map));
	54	append_payload(logic);
	55	}
	56
	57	LogicSnapshot::~LogicSnapshot()
	58	{
	59	lock_guard<recursive_mutex> lock(_mutex);
	60	for (MipMapLevel &l : _mip_map)
	61	free(l.data);
	62	}
	63
	64	uint64_t LogicSnapshot::unpack_sample(const uint8_t *ptr) const
	65	{
	66	#ifdef HAVE_UNALIGNED_LITTLE_ENDIAN_ACCESS
	67	return (uint64_t)ptr;
	68	#else
	69	uint64_t value = 0;
	70	switch(_unit_size) {
	71	default:
	72	value \|= ((uint64_t)ptr[7]) << 56;
	73	/* FALLTHRU */
	74	case 7:
	75	value \|= ((uint64_t)ptr[6]) << 48;
	76	/* FALLTHRU */
	77	case 6:
	78	value \|= ((uint64_t)ptr[5]) << 40;
	79	/* FALLTHRU */
	80	case 5:
	81	value \|= ((uint64_t)ptr[4]) << 32;
	82	/* FALLTHRU */
	83	case 4:
	84	value \|= ((uint32_t)ptr[3]) << 24;
	85	/* FALLTHRU */
	86	case 3:
	87	value \|= ((uint32_t)ptr[2]) << 16;
	88	/* FALLTHRU */
	89	case 2:
	90	value \|= ptr[1] << 8;
	91	/* FALLTHRU */
	92	case 1:
	93	value \|= ptr[0];
	94	/* FALLTHRU */
	95	case 0:
	96	break;
	97	}
	98	return value;
	99	#endif
	100	}
	101
	102	void LogicSnapshot::pack_sample(uint8_t *ptr, uint64_t value)
	103	{
	104	#ifdef HAVE_UNALIGNED_LITTLE_ENDIAN_ACCESS
	105	(uint64_t)ptr = value;
	106	#else
	107	switch(_unit_size) {
	108	default:
	109	ptr[7] = value >> 56;
	110	/* FALLTHRU */
	111	case 7:
	112	ptr[6] = value >> 48;
	113	/* FALLTHRU */
	114	case 6:
	115	ptr[5] = value >> 40;
	116	/* FALLTHRU */
	117	case 5:
	118	ptr[4] = value >> 32;
	119	/* FALLTHRU */
	120	case 4:
	121	ptr[3] = value >> 24;
	122	/* FALLTHRU */
	123	case 3:
	124	ptr[2] = value >> 16;
	125	/* FALLTHRU */
	126	case 2:
	127	ptr[1] = value >> 8;
	128	/* FALLTHRU */
	129	case 1:
	130	ptr[0] = value;
	131	/* FALLTHRU */
	132	case 0:
	133	break;
	134	}
	135	#endif
	136	}
	137
	138	void LogicSnapshot::append_payload(
	139	const sr_datafeed_logic &logic)
	140	{
	141	assert(_unit_size == logic.unitsize);
	142	assert((logic.length % _unit_size) == 0);
	143
	144	lock_guard<recursive_mutex> lock(_mutex);
	145
	146	append_data(logic.data, logic.length / _unit_size);
	147
	148	// Generate the first mip-map from the data
	149	append_payload_to_mipmap();
	150	}
	151
	152	void LogicSnapshot::get_samples(uint8_t *const data,
	153	int64_t start_sample, int64_t end_sample) const
	154	{
	155	assert(data);
	156	assert(start_sample >= 0);
	157	assert(start_sample <= (int64_t)_sample_count);
	158	assert(end_sample >= 0);
	159	assert(end_sample <= (int64_t)_sample_count);
	160	assert(start_sample <= end_sample);
	161
	162	lock_guard<recursive_mutex> lock(_mutex);
	163
	164	const size_t size = (end_sample - start_sample) * _unit_size;
	165	memcpy(data, (const uint8_t)_data + start_sample _unit_size, size);
	166	}
	167
	168	void LogicSnapshot::reallocate_mipmap_level(MipMapLevel &m)
	169	{
	170	const uint64_t new_data_length = ((m.length + MipMapDataUnit - 1) /
	171	MipMapDataUnit) * MipMapDataUnit;
	172	if (new_data_length > m.data_length)
	173	{
	174	m.data_length = new_data_length;
	175
	176	// Padding is added to allow for the uint64_t write word
	177	m.data = realloc(m.data, new_data_length * _unit_size +
	178	sizeof(uint64_t));
	179	}
	180	}
	181
	182	void LogicSnapshot::append_payload_to_mipmap()
	183	{
	184	MipMapLevel &m0 = _mip_map[0];
	185	uint64_t prev_length;
	186	const uint8_t *src_ptr;
	187	uint8_t *dest_ptr;
	188	uint64_t accumulator;
	189	unsigned int diff_counter;
	190
	191	// Expand the data buffer to fit the new samples
	192	prev_length = m0.length;
	193	m0.length = _sample_count / MipMapScaleFactor;
	194
	195	// Break off if there are no new samples to compute
	196	if (m0.length == prev_length)
	197	return;
	198
	199	reallocate_mipmap_level(m0);
	200
	201	dest_ptr = (uint8_t)m0.data + prev_length _unit_size;
	202
	203	// Iterate through the samples to populate the first level mipmap
	204	const uint8_t const end_src_ptr = (uint8_t)_data +
	205	m0.length * _unit_size * MipMapScaleFactor;
	206	for (src_ptr = (uint8_t*)_data +
	207	prev_length * _unit_size * MipMapScaleFactor;
	208	src_ptr < end_src_ptr;)
	209	{
	210	// Accumulate transitions which have occurred in this sample
	211	accumulator = 0;
	212	diff_counter = MipMapScaleFactor;
	213	while (diff_counter-- > 0)
	214	{
	215	const uint64_t sample = unpack_sample(src_ptr);
	216	accumulator \|= _last_append_sample ^ sample;
	217	_last_append_sample = sample;
	218	src_ptr += _unit_size;
	219	}
	220
	221	pack_sample(dest_ptr, accumulator);
	222	dest_ptr += _unit_size;
	223	}
	224
	225	// Compute higher level mipmaps
	226	for (unsigned int level = 1; level < ScaleStepCount; level++)
	227	{
	228	MipMapLevel &m = _mip_map[level];
	229	const MipMapLevel &ml = _mip_map[level-1];
	230
	231	// Expand the data buffer to fit the new samples
	232	prev_length = m.length;
	233	m.length = ml.length / MipMapScaleFactor;
	234
	235	// Break off if there are no more samples to computed
	236	if (m.length == prev_length)
	237	break;
	238
	239	reallocate_mipmap_level(m);
	240
	241	// Subsample the level lower level
	242	src_ptr = (uint8_t*)ml.data +
	243	_unit_size * prev_length * MipMapScaleFactor;
	244	const uint8_t *const end_dest_ptr =
	245	(uint8_t)m.data + _unit_size m.length;
	246	for (dest_ptr = (uint8_t*)m.data +
	247	_unit_size * prev_length;
	248	dest_ptr < end_dest_ptr;
	249	dest_ptr += _unit_size)
	250	{
	251	accumulator = 0;
	252	diff_counter = MipMapScaleFactor;
	253	while (diff_counter-- > 0)
	254	{
	255	accumulator \|= unpack_sample(src_ptr);
	256	src_ptr += _unit_size;
	257	}
	258
	259	pack_sample(dest_ptr, accumulator);
	260	}
	261	}
	262	}
	263
	264	uint64_t LogicSnapshot::get_sample(uint64_t index) const
	265	{
	266	assert(_data);
	267	assert(index < _sample_count);
	268
	269	return unpack_sample((uint8_t)_data + index _unit_size);
	270	}
	271
	272	void LogicSnapshot::get_subsampled_edges(
	273	std::vector<EdgePair> &edges,
	274	uint64_t start, uint64_t end,
	275	float min_length, int sig_index)
	276	{
	277	uint64_t index = start;
	278	unsigned int level;
	279	bool last_sample;
	280	bool fast_forward;
	281
	282	assert(end <= get_sample_count());
	283	assert(start <= end);
	284	assert(min_length > 0);
	285	assert(sig_index >= 0);
	286	assert(sig_index < 64);
	287
	288	lock_guard<recursive_mutex> lock(_mutex);
	289
	290	const uint64_t block_length = (uint64_t)max(min_length, 1.0f);
	291	const unsigned int min_level = max((int)floorf(logf(min_length) /
	292	LogMipMapScaleFactor) - 1, 0);
	293	const uint64_t sig_mask = 1ULL << sig_index;
	294
	295	// Store the initial state
	296	last_sample = (get_sample(start) & sig_mask) != 0;
	297	edges.push_back(pair<int64_t, bool>(index++, last_sample));
	298
	299	while (index + block_length <= end)
	300	{
	301	//----- Continue to search -----//
	302	level = min_level;
	303
	304	// We cannot fast-forward if there is no mip-map data at
	305	// at the minimum level.
	306	fast_forward = (_mip_map[level].data != NULL);
	307
	308	if (min_length < MipMapScaleFactor)
	309	{
	310	// Search individual samples up to the beginning of
	311	// the next first level mip map block
	312	const uint64_t final_index = min(end,
	313	pow2_ceil(index, MipMapScalePower));
	314
	315	for (; index < final_index &&
	316	(index & ~(~0 << MipMapScalePower)) != 0;
	317	index++)
	318	{
	319	const bool sample =
	320	(get_sample(index) & sig_mask) != 0;
	321
	322	// If there was a change we cannot fast forward
	323	if (sample != last_sample) {
	324	fast_forward = false;
	325	break;
	326	}
	327	}
	328	}
	329	else
	330	{
	331	// If resolution is less than a mip map block,
	332	// round up to the beginning of the mip-map block
	333	// for this level of detail
	334	const int min_level_scale_power =
	335	(level + 1) * MipMapScalePower;
	336	index = pow2_ceil(index, min_level_scale_power);
	337	if (index >= end)
	338	break;
	339
	340	// We can fast forward only if there was no change
	341	const bool sample =
	342	(get_sample(index) & sig_mask) != 0;
	343	if (last_sample != sample)
	344	fast_forward = false;
	345	}
	346
	347	if (fast_forward) {
	348
	349	// Fast forward: This involves zooming out to higher
	350	// levels of the mip map searching for changes, then
	351	// zooming in on them to find the point where the edge
	352	// begins.
	353
	354	// Slide right and zoom out at the beginnings of mip-map
	355	// blocks until we encounter a change
	356	while (1) {
	357	const int level_scale_power =
	358	(level + 1) * MipMapScalePower;
	359	const uint64_t offset =
	360	index >> level_scale_power;
	361
	362	// Check if we reached the last block at this
	363	// level, or if there was a change in this block
	364	if (offset >= _mip_map[level].length \|\|
	365	(get_subsample(level, offset) &
	366	sig_mask))
	367	break;
	368
	369	if ((offset & ~(~0 << MipMapScalePower)) == 0) {
	370	// If we are now at the beginning of a
	371	// higher level mip-map block ascend one
	372	// level
	373	if (level + 1 >= ScaleStepCount \|\|
	374	!_mip_map[level + 1].data)
	375	break;
	376
	377	level++;
	378	} else {
	379	// Slide right to the beginning of the
	380	// next mip map block
	381	index = pow2_ceil(index + 1,
	382	level_scale_power);
	383	}
	384	}
	385
	386	// Zoom in, and slide right until we encounter a change,
	387	// and repeat until we reach min_level
	388	while (1) {
	389	assert(_mip_map[level].data);
	390
	391	const int level_scale_power =
	392	(level + 1) * MipMapScalePower;
	393	const uint64_t offset =
	394	index >> level_scale_power;
	395
	396	// Check if we reached the last block at this
	397	// level, or if there was a change in this block
	398	if (offset >= _mip_map[level].length \|\|
	399	(get_subsample(level, offset) &
	400	sig_mask)) {
	401	// Zoom in unless we reached the minimum
	402	// zoom
	403	if (level == min_level)
	404	break;
	405
	406	level--;
	407	} else {
	408	// Slide right to the beginning of the
	409	// next mip map block
	410	index = pow2_ceil(index + 1,
	411	level_scale_power);
	412	}
	413	}
	414
	415	// If individual samples within the limit of resolution,
	416	// do a linear search for the next transition within the
	417	// block
	418	if (min_length < MipMapScaleFactor) {
	419	for (; index < end; index++) {
	420	const bool sample = (get_sample(index) &
	421	sig_mask) != 0;
	422	if (sample != last_sample)
	423	break;
	424	}
	425	}
	426	}
	427
	428	//----- Store the edge -----//
	429
	430	// Take the last sample of the quanization block
	431	const int64_t final_index = index + block_length;
	432	if (index + block_length > end)
	433	break;
	434
	435	// Store the final state
	436	const bool final_sample =
	437	(get_sample(final_index - 1) & sig_mask) != 0;
	438	edges.push_back(pair<int64_t, bool>(index, final_sample));
	439
	440	index = final_index;
	441	last_sample = final_sample;
	442	}
	443
	444	// Add the final state
	445	const bool end_sample = get_sample(end) & sig_mask;
	446	if (last_sample != end_sample)
	447	edges.push_back(pair<int64_t, bool>(end, end_sample));
	448	edges.push_back(pair<int64_t, bool>(end + 1, end_sample));
	449	}
	450
	451	uint64_t LogicSnapshot::get_subsample(int level, uint64_t offset) const
	452	{
	453	assert(level >= 0);
	454	assert(_mip_map[level].data);
	455	return unpack_sample((uint8_t*)_mip_map[level].data +
	456	_unit_size * offset);
	457	}
	458
	459	uint64_t LogicSnapshot::pow2_ceil(uint64_t x, unsigned int power)
	460	{
	461	const uint64_t p = 1 << power;
	462	return (x + p - 1) / p * p;
	463	}
	464
	465	} // namespace data
	466	} // namespace pv