The R Project SVN R

///////////////////////////////////////////////////////////////////////////////
//
/// \file       index_encoder.c
/// \brief      Encodes the Index field
//
//  Author:     Lasse Collin
//
//  This file has been put into the public domain.
//  You can do whatever you want with this file.
//
///////////////////////////////////////////////////////////////////////////////

#include "index_encoder.h"
#include "index.h"
#include "check.h"


struct lzma_coder_s {
    enum {
        SEQ_INDICATOR,
        SEQ_COUNT,
        SEQ_UNPADDED,
        SEQ_UNCOMPRESSED,
        SEQ_NEXT,
        SEQ_PADDING,
        SEQ_CRC32,
    } sequence;

    /// Index being encoded
    const lzma_index *index;

    /// Iterator for the Index being encoded
    lzma_index_iter iter;

    /// Position in integers
    size_t pos;

    /// CRC32 of the List of Records field
    uint32_t crc32;
};


static lzma_ret
index_encode(lzma_coder *coder,
        lzma_allocator *allocator lzma_attribute((__unused__)),
        const uint8_t *restrict in lzma_attribute((__unused__)),
        size_t *restrict in_pos lzma_attribute((__unused__)),
        size_t in_size lzma_attribute((__unused__)),
        uint8_t *restrict out, size_t *restrict out_pos,
        size_t out_size,
        lzma_action action lzma_attribute((__unused__)))
{
    // Position where to start calculating CRC32. The idea is that we
    // need to call lzma_crc32() only once per call to index_encode().
    const size_t out_start = *out_pos;

    // Return value to use if we return at the end of this function.
    // We use "goto out" to jump out of the while-switch construct
    // instead of returning directly, because that way we don't need
    // to copypaste the lzma_crc32() call to many places.
    lzma_ret ret = LZMA_OK;

    while (*out_pos < out_size)
    switch (coder->sequence) {
    case SEQ_INDICATOR:
        out[*out_pos] = 0x00;
        ++*out_pos;
        coder->sequence = SEQ_COUNT;
        break;

    case SEQ_COUNT: {
        const lzma_vli count = lzma_index_block_count(coder->index);
        ret = lzma_vli_encode(count, &coder->pos,
                out, out_pos, out_size);
        if (ret != LZMA_STREAM_END)
            goto out;

        ret = LZMA_OK;
        coder->pos = 0;
        coder->sequence = SEQ_NEXT;
        break;
    }

    case SEQ_NEXT:
        if (lzma_index_iter_next(
                &coder->iter, LZMA_INDEX_ITER_BLOCK)) {
            // Get the size of the Index Padding field.
            coder->pos = lzma_index_padding_size(coder->index);
            assert(coder->pos <= 3);
            coder->sequence = SEQ_PADDING;
            break;
        }

        coder->sequence = SEQ_UNPADDED;

    // Fall through

    case SEQ_UNPADDED:
    case SEQ_UNCOMPRESSED: {
        const lzma_vli size = coder->sequence == SEQ_UNPADDED
                ? coder->iter.block.unpadded_size
                : coder->iter.block.uncompressed_size;

        ret = lzma_vli_encode(size, &coder->pos,
                out, out_pos, out_size);
        if (ret != LZMA_STREAM_END)
            goto out;

        ret = LZMA_OK;
        coder->pos = 0;

        // Advance to SEQ_UNCOMPRESSED or SEQ_NEXT.
        ++coder->sequence;
        break;
    }

    case SEQ_PADDING:
        if (coder->pos > 0) {
            --coder->pos;
            out[(*out_pos)++] = 0x00;
            break;
        }

        // Finish the CRC32 calculation.
        coder->crc32 = lzma_crc32(out + out_start,
                *out_pos - out_start, coder->crc32);

        coder->sequence = SEQ_CRC32;

    // Fall through

    case SEQ_CRC32:
        // We don't use the main loop, because we don't want
        // coder->crc32 to be touched anymore.
        do {
            if (*out_pos == out_size)
                return LZMA_OK;

            out[*out_pos] = (coder->crc32 >> (coder->pos * 8))
                    & 0xFF;
            ++*out_pos;

        } while (++coder->pos < 4);

        return LZMA_STREAM_END;

    default:
        assert(0);
        return LZMA_PROG_ERROR;
    }

out:
    // Update the CRC32.
    coder->crc32 = lzma_crc32(out + out_start,
            *out_pos - out_start, coder->crc32);

    return ret;
}


static void
index_encoder_end(lzma_coder *coder, lzma_allocator *allocator)
{
    lzma_free(coder, allocator);
    return;
}


static void
index_encoder_reset(lzma_coder *coder, const lzma_index *i)
{
    lzma_index_iter_init(&coder->iter, i);

    coder->sequence = SEQ_INDICATOR;
    coder->index = i;
    coder->pos = 0;
    coder->crc32 = 0;

    return;
}


extern lzma_ret
lzma_index_encoder_init(lzma_next_coder *next, lzma_allocator *allocator,
        const lzma_index *i)
{
    lzma_next_coder_init(&lzma_index_encoder_init, next, allocator);

    if (i == NULL)
        return LZMA_PROG_ERROR;

    if (next->coder == NULL) {
        next->coder = lzma_alloc(sizeof(lzma_coder), allocator);
        if (next->coder == NULL)
            return LZMA_MEM_ERROR;

        next->code = &index_encode;
        next->end = &index_encoder_end;
    }

    index_encoder_reset(next->coder, i);

    return LZMA_OK;
}


extern LZMA_API(lzma_ret)
lzma_index_encoder(lzma_stream *strm, const lzma_index *i)
{
    lzma_next_strm_init(lzma_index_encoder_init, strm, i);

    strm->internal->supported_actions[LZMA_RUN] = true;
    strm->internal->supported_actions[LZMA_FINISH] = true;

    return LZMA_OK;
}


extern LZMA_API(lzma_ret)
lzma_index_buffer_encode(const lzma_index *i,
        uint8_t *out, size_t *out_pos, size_t out_size)
{
    // Validate the arguments.
    if (i == NULL || out == NULL || out_pos == NULL || *out_pos > out_size)
        return LZMA_PROG_ERROR;

    // Don't try to encode if there's not enough output space.
    if (out_size - *out_pos < lzma_index_size(i))
        return LZMA_BUF_ERROR;

    // The Index encoder needs just one small data structure so we can
    // allocate it on stack.
    lzma_coder coder;
    index_encoder_reset(&coder, i);

    // Do the actual encoding. This should never fail, but store
    // the original *out_pos just in case.
    const size_t out_start = *out_pos;
    lzma_ret ret = index_encode(&coder, NULL, NULL, NULL, 0,
            out, out_pos, out_size, LZMA_RUN);

    if (ret == LZMA_STREAM_END) {
        ret = LZMA_OK;
    } else {
        // We should never get here, but just in case, restore the
        // output position and set the error accordingly if something
        // goes wrong and debugging isn't enabled.
        assert(0);
        *out_pos = out_start;
        ret = LZMA_PROG_ERROR;
    }

    return ret;
}