root/src/liblzma/common/vli_decoder.c

DEFINITIONS

1. LZMA_API

///////////////////////////////////////////////////////////////////////////////
//
/// \file       vli_decoder.c
/// \brief      Decodes variable-length integers
//
//  Author:     Lasse Collin
//
//  This file has been put into the public domain.
//  You can do whatever you want with this file.
//
///////////////////////////////////////////////////////////////////////////////

#include "common.h"


extern LZMA_API(lzma_ret)
lzma_vli_decode(lzma_vli *restrict vli, size_t *vli_pos,
                const uint8_t *restrict in, size_t *restrict in_pos,
                size_t in_size)
{
        // If we haven't been given vli_pos, work in single-call mode.
        size_t vli_pos_internal = 0;
        if (vli_pos == NULL) {
                vli_pos = &vli_pos_internal;
                *vli = 0;

                // If there's no input, use LZMA_DATA_ERROR. This way it is
                // easy to decode VLIs from buffers that have known size,
                // and get the correct error code in case the buffer is
                // too short.
                if (*in_pos >= in_size)
                        return LZMA_DATA_ERROR;

        } else {
                // Initialize *vli when starting to decode a new integer.
                if (*vli_pos == 0)
                        *vli = 0;

                // Validate the arguments.
                if (*vli_pos >= LZMA_VLI_BYTES_MAX
                                || (*vli >> (*vli_pos * 7)) != 0)
                        return LZMA_PROG_ERROR;;

                if (*in_pos >= in_size)
                        return LZMA_BUF_ERROR;
        }

        do {
                // Read the next byte. Use a temporary variable so that we
                // can update *in_pos immediately.
                const uint8_t byte = in[*in_pos];
                ++*in_pos;

                // Add the newly read byte to *vli.
                *vli += (lzma_vli)(byte & 0x7F) << (*vli_pos * 7);
                ++*vli_pos;

                // Check if this is the last byte of a multibyte integer.
                if ((byte & 0x80) == 0) {
                        // We don't allow using variable-length integers as
                        // padding i.e. the encoding must use the most the
                        // compact form.
                        if (byte == 0x00 && *vli_pos > 1)
                                return LZMA_DATA_ERROR;

                        return vli_pos == &vli_pos_internal
                                        ? LZMA_OK : LZMA_STREAM_END;
                }

                // There is at least one more byte coming. If we have already
                // read maximum number of bytes, the integer is considered
                // corrupt.
                //
                // If we need bigger integers in future, old versions liblzma
                // will confusingly indicate the file being corrupt istead of
                // unsupported. I suppose it's still better this way, because
                // in the foreseeable future (writing this in 2008) the only
                // reason why files would appear having over 63-bit integers
                // is that the files are simply corrupt.
                if (*vli_pos == LZMA_VLI_BYTES_MAX)
                        return LZMA_DATA_ERROR;

        } while (*in_pos < in_size);

        return vli_pos == &vli_pos_internal ? LZMA_DATA_ERROR : LZMA_OK;
}