xz/src/liblzma/rangecoder/range_encoder.h

///////////////////////////////////////////////////////////////////////////////
//
/// \file       range_encoder.h
/// \brief      Range Encoder
//
//  Copyright (C) 1999-2006 Igor Pavlov
//  Copyright (C) 2007-2008 Lasse Collin
//
//  This library 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.
//
//  This library 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.
//
///////////////////////////////////////////////////////////////////////////////

#ifndef LZMA_RANGE_ENCODER_H
#define LZMA_RANGE_ENCODER_H

#include "range_common.h"


/// Maximum number of symbols that can be put pending into lzma_range_encoder
/// structure between calls to lzma_rc_encode(). For LZMA, 52+5 is enough
/// (match with big distance and length followed by range encoder flush).
#define RC_SYMBOLS_MAX 58


typedef struct {
	uint64_t low;
	uint64_t cache_size;
	uint32_t range;
	uint8_t cache;

	/// Number of symbols in the tables
	size_t count;

	/// rc_encode()'s position in the tables
	size_t pos;

	/// Symbols to encode
	enum {
		RC_BIT_0,
		RC_BIT_1,
		RC_DIRECT_0,
		RC_DIRECT_1,
		RC_FLUSH,
	} symbols[RC_SYMBOLS_MAX];

	/// Probabilities associated with RC_BIT_0 or RC_BIT_1
	probability *probs[RC_SYMBOLS_MAX];

} lzma_range_encoder;


static inline void
rc_reset(lzma_range_encoder *rc)
{
	rc->low = 0;
	rc->cache_size = 1;
	rc->range = UINT32_MAX;
	rc->cache = 0;
	rc->count = 0;
	rc->pos = 0;
}


static inline void
rc_bit(lzma_range_encoder *rc, probability *prob, uint32_t bit)
{
	rc->symbols[rc->count] = bit;
	rc->probs[rc->count] = prob;
	++rc->count;
}


static inline void
rc_bittree(lzma_range_encoder *rc, probability *probs,
		uint32_t bit_count, uint32_t symbol)
{
	uint32_t model_index = 1;

	do {
		const uint32_t bit = (symbol >> --bit_count) & 1;
		rc_bit(rc, &probs[model_index], bit);
		model_index = (model_index << 1) | bit;
	} while (bit_count != 0);
}


static inline void
rc_bittree_reverse(lzma_range_encoder *rc, probability *probs,
		uint32_t bit_count, uint32_t symbol)
{
	uint32_t model_index = 1;

	do {
		const uint32_t bit = symbol & 1;
		symbol >>= 1;
		rc_bit(rc, &probs[model_index], bit);
		model_index = (model_index << 1) | bit;
	} while (--bit_count != 0);
}


static inline void
rc_direct(lzma_range_encoder *rc,
		uint32_t value, uint32_t bit_count)
{
	do {
		rc->symbols[rc->count++]
				= RC_DIRECT_0 + ((value >> --bit_count) & 1);
	} while (bit_count != 0);
}


static inline void
rc_flush(lzma_range_encoder *rc)
{
	for (size_t i = 0; i < 5; ++i)
		rc->symbols[rc->count++] = RC_FLUSH;
}


static inline bool
rc_shift_low(lzma_range_encoder *rc,
		uint8_t *out, size_t *out_pos, size_t out_size)
{
	if ((uint32_t)(rc->low) < (uint32_t)(0xFF000000)
			|| (uint32_t)(rc->low >> 32) != 0) {
		do {
			if (*out_pos == out_size)
				return true;

			out[*out_pos] = rc->cache + (uint8_t)(rc->low >> 32);
			++*out_pos;
			rc->cache = 0xFF;

		} while (--rc->cache_size != 0);

		rc->cache = (rc->low >> 24) & 0xFF;
	}

	++rc->cache_size;
	rc->low = (rc->low & 0x00FFFFFF) << SHIFT_BITS;

	return false;
}


static inline bool
rc_encode(lzma_range_encoder *rc,
		uint8_t *out, size_t *out_pos, size_t out_size)
{
	while (rc->pos < rc->count) {
		// Normalize
		if (rc->range < TOP_VALUE) {
			if (rc_shift_low(rc, out, out_pos, out_size))
				return true;

			rc->range <<= SHIFT_BITS;
		}

		// Encode a bit
		switch (rc->symbols[rc->pos]) {
		case RC_BIT_0: {
			probability prob = *rc->probs[rc->pos];
			rc->range = (rc->range >> BIT_MODEL_TOTAL_BITS) * prob;
			prob += (BIT_MODEL_TOTAL - prob) >> MOVE_BITS;
			*rc->probs[rc->pos] = prob;
			break;
		}

		case RC_BIT_1: {
			probability prob = *rc->probs[rc->pos];
			const uint32_t bound = prob
					* (rc->range >> BIT_MODEL_TOTAL_BITS);
			rc->low += bound;
			rc->range -= bound;
			prob -= prob >> MOVE_BITS;
			*rc->probs[rc->pos] = prob;
			break;
		}

		case RC_DIRECT_0:
			rc->range >>= 1;
			break;

		case RC_DIRECT_1:
			rc->range >>= 1;
			rc->low += rc->range;
			break;

		case RC_FLUSH:
			// Prevent further normalizations.
			rc->range = UINT32_MAX;

			// Flush the last five bytes (see rc_flush()).
			do {
				if (rc_shift_low(rc, out, out_pos, out_size))
					return true;
			} while (++rc->pos < rc->count);

			// Reset the range encoder so we are ready to continue
			// encoding if we weren't finishing the stream.
			rc_reset(rc);
			return false;

		default:
			assert(0);
			break;
		}

		++rc->pos;
	}

	rc->count = 0;
	rc->pos = 0;

	return false;
}


static inline uint64_t
rc_pending(const lzma_range_encoder *rc)
{
	return rc->cache_size + 5 - 1;
}


////////////
// Prices //
////////////

#ifdef HAVE_SMALL
/// Probability prices used by *_get_price() macros. This is initialized
/// by lzma_rc_init() and is not modified later.
extern uint32_t lzma_rc_prob_prices[BIT_MODEL_TOTAL >> MOVE_REDUCING_BITS];

/// Initializes lzma_rc_prob_prices[]. This needs to be called only once.
extern void lzma_rc_init(void);

#else
// Not building a size optimized version, so we use a precomputed
// constant table.
extern const uint32_t
lzma_rc_prob_prices[BIT_MODEL_TOTAL >> MOVE_REDUCING_BITS];

#endif


#define bit_get_price(prob, symbol) \
	lzma_rc_prob_prices[((((prob) - (symbol)) ^ (-(symbol))) \
			& (BIT_MODEL_TOTAL - 1)) >> MOVE_REDUCING_BITS]


#define bit_get_price_0(prob) \
	lzma_rc_prob_prices[(prob) >> MOVE_REDUCING_BITS]


#define bit_get_price_1(prob) \
	lzma_rc_prob_prices[(BIT_MODEL_TOTAL - (prob)) >> MOVE_REDUCING_BITS]


static inline uint32_t
bittree_get_price(const probability *probs,
		uint32_t bit_levels, uint32_t symbol)
{
	uint32_t price = 0;
	symbol |= UINT32_C(1) << bit_levels;

	do {
		price += bit_get_price(probs[symbol >> 1], symbol & 1);
		symbol >>= 1;
	} while (symbol != 1);

	return price;
}


static inline uint32_t
bittree_reverse_get_price(const probability *probs,
		uint32_t bit_levels, uint32_t symbol)
{
	uint32_t price = 0;
	uint32_t model_index = 1;

	do {
		const uint32_t bit = symbol & 1;
		symbol >>= 1;
		price += bit_get_price(probs[model_index], bit);
		model_index = (model_index << 1) | bit;
	} while (--bit_levels != 0);

	return price;
}

#endif