source: vbox/trunk/src/libs/liblzma-5.4.1/lz/lz_decoder.h

///////////////////////////////////////////////////////////////////////////////
//
/// \file       lz_decoder.h
/// \brief      LZ out window
///
//  Authors:    Igor Pavlov
//              Lasse Collin
//
//  This file has been put into the public domain.
//  You can do whatever you want with this file.
//
///////////////////////////////////////////////////////////////////////////////

#ifndef LZMA_LZ_DECODER_H
#define LZMA_LZ_DECODER_H

#include "common.h"


typedef struct {
        /// Pointer to the dictionary buffer. It can be an allocated buffer
        /// internal to liblzma, or it can a be a buffer given by the
        /// application when in single-call mode (not implemented yet).
        uint8_t *buf;

        /// Write position in dictionary. The next byte will be written to
        /// buf[pos].
        size_t pos;

        /// Indicates how full the dictionary is. This is used by
        /// dict_is_distance_valid() to detect corrupt files that would
        /// read beyond the beginning of the dictionary.
        size_t full;

        /// Write limit
        size_t limit;

        /// Size of the dictionary
        size_t size;

        /// True when dictionary should be reset before decoding more data.
        bool need_reset;

} lzma_dict;


typedef struct {
        size_t dict_size;
        const uint8_t *preset_dict;
        size_t preset_dict_size;
} lzma_lz_options;


typedef struct {
        /// Data specific to the LZ-based decoder
        void *coder;

        /// Function to decode from in[] to *dict
        lzma_ret (*code)(void *coder,
                        lzma_dict *restrict dict, const uint8_t *restrict in,
                        size_t *restrict in_pos, size_t in_size);

        void (*reset)(void *coder, const void *options);

        /// Set the uncompressed size. If uncompressed_size == LZMA_VLI_UNKNOWN
        /// then allow_eopm will always be true.
        void (*set_uncompressed)(void *coder, lzma_vli uncompressed_size,
                        bool allow_eopm);

        /// Free allocated resources
        void (*end)(void *coder, const lzma_allocator *allocator);

} lzma_lz_decoder;


#define LZMA_LZ_DECODER_INIT \
        (lzma_lz_decoder){ \
                .coder = NULL, \
                .code = NULL, \
                .reset = NULL, \
                .set_uncompressed = NULL, \
                .end = NULL, \
        }


extern lzma_ret lzma_lz_decoder_init(lzma_next_coder *next,
                const lzma_allocator *allocator,
                const lzma_filter_info *filters,
                lzma_ret (*lz_init)(lzma_lz_decoder *lz,
                        const lzma_allocator *allocator,
                        lzma_vli id, const void *options,
                        lzma_lz_options *lz_options));

extern uint64_t lzma_lz_decoder_memusage(size_t dictionary_size);


//////////////////////
// Inline functions //
//////////////////////

/// Get a byte from the history buffer.
static inline uint8_t
dict_get(const lzma_dict *const dict, const uint32_t distance)
{
        return dict->buf[dict->pos - distance - 1
                        + (distance < dict->pos ? 0 : dict->size)];
}


/// Test if dictionary is empty.
static inline bool
dict_is_empty(const lzma_dict *const dict)
{
        return dict->full == 0;
}


/// Validate the match distance
static inline bool
dict_is_distance_valid(const lzma_dict *const dict, const size_t distance)
{
        return dict->full > distance;
}


/// Repeat *len bytes at distance.
static inline bool
dict_repeat(lzma_dict *dict, uint32_t distance, uint32_t *len)
{
        // Don't write past the end of the dictionary.
        const size_t dict_avail = dict->limit - dict->pos;
        uint32_t left = my_min(dict_avail, *len);
        *len -= left;

        // Repeat a block of data from the history. Because memcpy() is faster
        // than copying byte by byte in a loop, the copying process gets split
        // into three cases.
        if (distance < left) {
                // Source and target areas overlap, thus we can't use
                // memcpy() nor even memmove() safely.
                do {
                        dict->buf[dict->pos] = dict_get(dict, distance);
                        ++dict->pos;
                } while (--left > 0);

        } else if (distance < dict->pos) {
                // The easiest and fastest case
                memcpy(dict->buf + dict->pos,
                                dict->buf + dict->pos - distance - 1,
                                left);
                dict->pos += left;

        } else {
                // The bigger the dictionary, the more rare this
                // case occurs. We need to "wrap" the dict, thus
                // we might need two memcpy() to copy all the data.
                assert(dict->full == dict->size);
                const uint32_t copy_pos
                                = dict->pos - distance - 1 + dict->size;
                uint32_t copy_size = dict->size - copy_pos;

                if (copy_size < left) {
                        memmove(dict->buf + dict->pos, dict->buf + copy_pos,
                                        copy_size);
                        dict->pos += copy_size;
                        copy_size = left - copy_size;
                        memcpy(dict->buf + dict->pos, dict->buf, copy_size);
                        dict->pos += copy_size;
                } else {
                        memmove(dict->buf + dict->pos, dict->buf + copy_pos,
                                        left);
                        dict->pos += left;
                }
        }

        // Update how full the dictionary is.
        if (dict->full < dict->pos)
                dict->full = dict->pos;

        return unlikely(*len != 0);
}


/// Puts one byte into the dictionary. Returns true if the dictionary was
/// already full and the byte couldn't be added.
static inline bool
dict_put(lzma_dict *dict, uint8_t byte)
{
        if (unlikely(dict->pos == dict->limit))
                return true;

        dict->buf[dict->pos++] = byte;

        if (dict->pos > dict->full)
                dict->full = dict->pos;

        return false;
}


/// Copies arbitrary amount of data into the dictionary.
static inline void
dict_write(lzma_dict *restrict dict, const uint8_t *restrict in,
                size_t *restrict in_pos, size_t in_size,
                size_t *restrict left)
{
        // NOTE: If we are being given more data than the size of the
        // dictionary, it could be possible to optimize the LZ decoder
        // so that not everything needs to go through the dictionary.
        // This shouldn't be very common thing in practice though, and
        // the slowdown of one extra memcpy() isn't bad compared to how
        // much time it would have taken if the data were compressed.

        if (in_size - *in_pos > *left)
                in_size = *in_pos + *left;

        *left -= lzma_bufcpy(in, in_pos, in_size,
                        dict->buf, &dict->pos, dict->limit);

        if (dict->pos > dict->full)
                dict->full = dict->pos;

        return;
}


static inline void
dict_reset(lzma_dict *dict)
{
        dict->need_reset = true;
        return;
}

#endif