The R Project SVN R

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

#include "delta_decoder.h"
#include "delta_private.h"


static void
decode_buffer(lzma_coder *coder, uint8_t *buffer, size_t size)
{
    const size_t distance = coder->distance;

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


static lzma_ret
delta_decode(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)
{
    assert(coder->next.code != NULL);

    const size_t out_start = *out_pos;

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

    decode_buffer(coder, out + out_start, *out_pos - out_start);

    return ret;
}


extern lzma_ret
lzma_delta_decoder_init(lzma_next_coder *next, lzma_allocator *allocator,
        const lzma_filter_info *filters)
{
    next->code = &delta_decode;
    return lzma_delta_coder_init(next, allocator, filters);
}


extern lzma_ret
lzma_delta_props_decode(void **options, lzma_allocator *allocator,
        const uint8_t *props, size_t props_size)
{
    if (props_size != 1)
        return LZMA_OPTIONS_ERROR;

    lzma_options_delta *opt
            = lzma_alloc(sizeof(lzma_options_delta), allocator);
    if (opt == NULL)
        return LZMA_MEM_ERROR;

    opt->type = LZMA_DELTA_TYPE_BYTE;
    opt->dist = props[0] + 1;

    *options = opt;

    return LZMA_OK;
}