The R Project SVN R

///////////////////////////////////////////////////////////////////////////////
//
/// \file       delta_encoder.c
/// \brief      Delta filter encoder
//
//  Author:     Lasse Collin
//
//  This file has been put into the public domain.
//  You can do whatever you want with this file.
//
///////////////////////////////////////////////////////////////////////////////

#include "delta_encoder.h"
#include "delta_private.h"


/// Copies and encodes the data at the same time. This is used when Delta
/// is the first filter in the chain (and thus the last filter in the
/// encoder's filter stack).
static void
copy_and_encode(lzma_coder *coder,
        const uint8_t *restrict in, uint8_t *restrict out, size_t size)
{
    const size_t distance = coder->distance;

    for (size_t i = 0; i < size; ++i) {
        const uint8_t tmp = coder->history[
                (distance + coder->pos) & 0xFF];
        coder->history[coder->pos-- & 0xFF] = in[i];
        out[i] = in[i] - tmp;
    }
}


/// Encodes the data in place. This is used when we are the last filter
/// in the chain (and thus non-last filter in the encoder's filter stack).
static void
encode_in_place(lzma_coder *coder, uint8_t *buffer, size_t size)
{
    const size_t distance = coder->distance;

    for (size_t i = 0; i < size; ++i) {
        const uint8_t tmp = coder->history[
                (distance + coder->pos) & 0xFF];
        coder->history[coder->pos-- & 0xFF] = buffer[i];
        buffer[i] -= tmp;
    }
}


static lzma_ret
delta_encode(lzma_coder *coder, lzma_allocator *allocator,
        const uint8_t *restrict in, size_t *restrict in_pos,
        size_t in_size, uint8_t *restrict out,
        size_t *restrict out_pos, size_t out_size, lzma_action action)
{
    lzma_ret ret;

    if (coder->next.code == NULL) {
        const size_t in_avail = in_size - *in_pos;
        const size_t out_avail = out_size - *out_pos;
        const size_t size = MIN(in_avail, out_avail);

        copy_and_encode(coder, in + *in_pos, out + *out_pos, size);

        *in_pos += size;
        *out_pos += size;

        ret = action != LZMA_RUN && *in_pos == in_size
                ? LZMA_STREAM_END : LZMA_OK;

    } else {
        const size_t out_start = *out_pos;

        ret = coder->next.code(coder->next.coder, allocator,
                in, in_pos, in_size, out, out_pos, out_size,
                action);

        encode_in_place(coder, out + out_start, *out_pos - out_start);
    }

    return ret;
}


extern lzma_ret
lzma_delta_encoder_init(lzma_next_coder *next, lzma_allocator *allocator,
        const lzma_filter_info *filters)
{
    return lzma_delta_coder_init(next, allocator, filters, &delta_encode);
}


extern lzma_ret
lzma_delta_props_encode(const void *options, uint8_t *out)
{
    // The caller must have already validated the options, so it's
    // LZMA_PROG_ERROR if they are invalid.
    if (lzma_delta_coder_memusage(options) == UINT64_MAX)
        return LZMA_PROG_ERROR;

    const lzma_options_delta *opt = options;
    out[0] = opt->dist - LZMA_DELTA_DIST_MIN;

    return LZMA_OK;
}