// SPDX-License-Identifier: 0BSD

///////////////////////////////////////////////////////////////////////////////

//

/// \file       vli_decoder.c

/// \brief      Decodes variable-length integers

//

//  Author:     Lasse Collin

//

///////////////////////////////////////////////////////////////////////////////

#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 instead 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;

}