The R Project SVN R

///////////////////////////////////////////////////////////////////////////////
//
/// \file       block_header_encoder.c
/// \brief      Encodes Block Header for .xz files
//
//  Author:     Lasse Collin
//
//  This file has been put into the public domain.
//  You can do whatever you want with this file.
//
///////////////////////////////////////////////////////////////////////////////

#include "common.h"
#include "check.h"


extern LZMA_API(lzma_ret)
lzma_block_header_size(lzma_block *block)
{
    if (block->version != 0)
        return LZMA_OPTIONS_ERROR;

    // Block Header Size + Block Flags + CRC32.
    uint32_t size = 1 + 1 + 4;

    // Compressed Size
    if (block->compressed_size != LZMA_VLI_UNKNOWN) {
        const uint32_t add = lzma_vli_size(block->compressed_size);
        if (add == 0 || block->compressed_size == 0)
            return LZMA_PROG_ERROR;

        size += add;
    }

    // Uncompressed Size
    if (block->uncompressed_size != LZMA_VLI_UNKNOWN) {
        const uint32_t add = lzma_vli_size(block->uncompressed_size);
        if (add == 0)
            return LZMA_PROG_ERROR;

        size += add;
    }

    // List of Filter Flags
    if (block->filters == NULL || block->filters[0].id == LZMA_VLI_UNKNOWN)
        return LZMA_PROG_ERROR;

    for (size_t i = 0; block->filters[i].id != LZMA_VLI_UNKNOWN; ++i) {
        // Don't allow too many filters.
        if (i == LZMA_FILTERS_MAX)
            return LZMA_PROG_ERROR;

        uint32_t add;
        return_if_error(lzma_filter_flags_size(&add,
                block->filters + i));

        size += add;
    }

    // Pad to a multiple of four bytes.
    block->header_size = (size + 3) & ~UINT32_C(3);

    // NOTE: We don't verify that the encoded size of the Block stays
    // within limits. This is because it is possible that we are called
    // with exaggerated Compressed Size (e.g. LZMA_VLI_MAX) to reserve
    // space for Block Header, and later called again with lower,
    // real values.

    return LZMA_OK;
}


extern LZMA_API(lzma_ret)
lzma_block_header_encode(const lzma_block *block, uint8_t *out)
{
    // Validate everything but filters.
    if (lzma_block_unpadded_size(block) == 0
            || !lzma_vli_is_valid(block->uncompressed_size))
        return LZMA_PROG_ERROR;

    // Indicate the size of the buffer _excluding_ the CRC32 field.
    const size_t out_size = block->header_size - 4;

    // Store the Block Header Size.
    out[0] = out_size / 4;

    // We write Block Flags in pieces.
    out[1] = 0x00;
    size_t out_pos = 2;

    // Compressed Size
    if (block->compressed_size != LZMA_VLI_UNKNOWN) {
        return_if_error(lzma_vli_encode(block->compressed_size, NULL,
                out, &out_pos, out_size));

        out[1] |= 0x40;
    }

    // Uncompressed Size
    if (block->uncompressed_size != LZMA_VLI_UNKNOWN) {
        return_if_error(lzma_vli_encode(block->uncompressed_size, NULL,
                out, &out_pos, out_size));

        out[1] |= 0x80;
    }

    // Filter Flags
    if (block->filters == NULL || block->filters[0].id == LZMA_VLI_UNKNOWN)
        return LZMA_PROG_ERROR;

    size_t filter_count = 0;
    do {
        // There can be a maximum of four filters.
        if (filter_count == LZMA_FILTERS_MAX)
            return LZMA_PROG_ERROR;

        return_if_error(lzma_filter_flags_encode(
                block->filters + filter_count,
                out, &out_pos, out_size));

    } while (block->filters[++filter_count].id != LZMA_VLI_UNKNOWN);

    out[1] |= filter_count - 1;

    // Padding
    memzero(out + out_pos, out_size - out_pos);

    // CRC32
    unaligned_write32le(out + out_size, lzma_crc32(out, out_size, 0));

    return LZMA_OK;
}