source: vbox/trunk/src/libs/liblzma-5.8.1/rangecoder/range_encoder.h@ 108911

// SPDX-License-Identifier: 0BSD

///////////////////////////////////////////////////////////////////////////////
//
/// \file       range_encoder.h
/// \brief      Range Encoder
///
//  Authors:    Igor Pavlov
//              Lasse Collin
//
///////////////////////////////////////////////////////////////////////////////

#ifndef LZMA_RANGE_ENCODER_H
#define LZMA_RANGE_ENCODER_H

#include "range_common.h"
#include "price.h"


/// Maximum number of symbols that can be put pending into lzma_range_encoder
/// structure between calls to lzma_rc_encode(). For LZMA, 48+5 is enough
/// (match with big distance and length followed by range encoder flush).
#define RC_SYMBOLS_MAX 53


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

        /// Number of bytes written out by rc_encode() -> rc_shift_low()
        uint64_t out_total;

        /// 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->out_total = 0;
        rc->count = 0;
        rc->pos = 0;
}


static inline void
rc_forget(lzma_range_encoder *rc)
{
        // This must not be called when rc_encode() is partially done.
        assert(rc->pos == 0);
        rc->count = 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->out_total;
                        rc->cache = 0xFF;

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

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

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

        return false;
}


// NOTE: The last two arguments are uint64_t instead of size_t because in
// the dummy version these refer to the size of the whole range-encoded
// output stream, not just to the currently available output buffer space.
static inline bool
rc_shift_low_dummy(uint64_t *low, uint64_t *cache_size, uint8_t *cache,
                uint64_t *out_pos, uint64_t out_size)
{
        if ((uint32_t)(*low) < (uint32_t)(0xFF000000)
                        || (uint32_t)(*low >> 32) != 0) {
                do {
                        if (*out_pos == out_size)
                                return true;

                        ++*out_pos;
                        *cache = 0xFF;

                } while (--*cache_size != 0);

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

        ++*cache_size;
        *low = (*low & 0x00FFFFFF) << RC_SHIFT_BITS;

        return false;
}


static inline bool
rc_encode(lzma_range_encoder *rc,
                uint8_t *out, size_t *out_pos, size_t out_size)
{
        assert(rc->count <= RC_SYMBOLS_MAX);

        while (rc->pos < rc->count) {
                // Normalize
                if (rc->range < RC_TOP_VALUE) {
                        if (rc_shift_low(rc, out, out_pos, out_size))
                                return true;

                        rc->range <<= RC_SHIFT_BITS;
                }

                // Encode a bit
                switch (rc->symbols[rc->pos]) {
                case RC_BIT_0: {
                        probability prob = *rc->probs[rc->pos];
                        rc->range = (rc->range >> RC_BIT_MODEL_TOTAL_BITS)
                                        * prob;
                        prob += (RC_BIT_MODEL_TOTAL - prob) >> RC_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
                                        >> RC_BIT_MODEL_TOTAL_BITS);
                        rc->low += bound;
                        rc->range -= bound;
                        prob -= prob >> RC_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 bool
rc_encode_dummy(const lzma_range_encoder *rc, uint64_t out_limit)
{
        assert(rc->count <= RC_SYMBOLS_MAX);

        uint64_t low = rc->low;
        uint64_t cache_size = rc->cache_size;
        uint32_t range = rc->range;
        uint8_t cache = rc->cache;
        uint64_t out_pos = rc->out_total;

        size_t pos = rc->pos;

        while (true) {
                // Normalize
                if (range < RC_TOP_VALUE) {
                        if (rc_shift_low_dummy(&low, &cache_size, &cache,
                                        &out_pos, out_limit))
                                return true;

                        range <<= RC_SHIFT_BITS;
                }

                // This check is here because the normalization above must
                // be done before flushing the last bytes.
                if (pos == rc->count)
                        break;

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

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

                case RC_DIRECT_0:
                        range >>= 1;
                        break;

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

                case RC_FLUSH:
                default:
                        assert(0);
                        break;
                }

                ++pos;
        }

        // Flush the last bytes. This isn't in rc->symbols[] so we do
        // it after the above loop to take into account the size of
        // the flushing that will be done at the end of the stream.
        for (pos = 0; pos < 5; ++pos) {
                if (rc_shift_low_dummy(&low, &cache_size,
                                &cache, &out_pos, out_limit))
                        return true;
        }

        return false;
}


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

#endif