The R Project SVN R

///////////////////////////////////////////////////////////////////////////////
//
/// \file       delta_common.c
/// \brief      Common stuff for Delta encoder and decoder
//
//  Author:     Lasse Collin
//
//  This file has been put into the public domain.
//  You can do whatever you want with this file.
//
///////////////////////////////////////////////////////////////////////////////

#include "delta_common.h"
#include "delta_private.h"


static void
delta_coder_end(lzma_coder *coder, lzma_allocator *allocator)
{
    lzma_next_end(&coder->next, allocator);
    lzma_free(coder, allocator);
    return;
}


extern lzma_ret
lzma_delta_coder_init(lzma_next_coder *next, lzma_allocator *allocator,
        const lzma_filter_info *filters, lzma_code_function code)
{
    // Allocate memory for the decoder if needed.
    if (next->coder == NULL) {
        next->coder = lzma_alloc(sizeof(lzma_coder), allocator);
        if (next->coder == NULL)
            return LZMA_MEM_ERROR;

        // End function is the same for encoder and decoder.
        next->end = &delta_coder_end;
        next->coder->next = LZMA_NEXT_CODER_INIT;
    }

    // Coding function is different for encoder and decoder.
    next->code = code;

    // Validate the options.
    if (lzma_delta_coder_memusage(filters[0].options) == UINT64_MAX)
        return LZMA_OPTIONS_ERROR;

    // Set the delta distance.
    const lzma_options_delta *opt = filters[0].options;
    next->coder->distance = opt->dist;

    // Initialize the rest of the variables.
    next->coder->pos = 0;
    memzero(next->coder->history, LZMA_DELTA_DIST_MAX);

    // Initialize the next decoder in the chain, if any.
    return lzma_next_filter_init(&next->coder->next,
            allocator, filters + 1);
}


extern uint64_t
lzma_delta_coder_memusage(const void *options)
{
    const lzma_options_delta *opt = options;

    if (opt == NULL || opt->type != LZMA_DELTA_TYPE_BYTE
            || opt->dist < LZMA_DELTA_DIST_MIN
            || opt->dist > LZMA_DELTA_DIST_MAX)
        return UINT64_MAX;

    return sizeof(lzma_coder);
}