dmtxencodebase256.c

/**
 * libdmtx - Data Matrix Encoding/Decoding Library
 * Copyright 2011 Mike Laughton. All rights reserved.
 * Copyright 2012-2016 Vadim A. Misbakh-Soloviov. All rights reserved.
 *
 * See LICENSE file in the main project directory for full
 * terms of use and distribution.
 *
 * Contact:
 * Vadim A. Misbakh-Soloviov <dmtx@mva.name>
 * Mike Laughton <mike@dragonflylogic.com>
 *
 * \file dmtxencodebase256.c
 * \brief Base 256 encoding rules
 */

/**
 *
 *
 */
static void
EncodeNextChunkBase256(DmtxEncodeStream *stream)
{
   DmtxByte value;

   if(StreamInputHasNext(stream))
   {
      /* Check for FNC1 character, which needs to be sent in ASCII */
      value = StreamInputPeekNext(stream); CHKERR;
      if(stream->fnc1 != DmtxUndefined && (int)value == stream->fnc1) {
         EncodeChangeScheme(stream, DmtxSchemeAscii, DmtxUnlatchExplicit);

         StreamInputAdvanceNext(stream); CHKERR;
         AppendValueAscii(stream, DmtxValueFNC1); CHKERR;
         return;
      }

      value = StreamInputAdvanceNext(stream); CHKERR;
      AppendValueBase256(stream, value); CHKERR;
   }
}

/**
 *
 *
 */
static void
AppendValueBase256(DmtxEncodeStream *stream, DmtxByte value)
{
   CHKSCHEME(DmtxSchemeBase256);

   StreamOutputChainAppend(stream, Randomize255State(value, stream->output->length + 1)); CHKERR;
   stream->outputChainValueCount++;

   UpdateBase256ChainHeader(stream, DmtxUndefined); CHKERR;
}

/**
 * check remaining symbol capacity and remaining codewords
 * if the chain can finish perfectly at the end of symbol data words there is a
 * special one-byte length header value that can be used (i think ... read the
 * spec again before commiting to anything)
 */
static void
CompleteIfDoneBase256(DmtxEncodeStream *stream, int sizeIdxRequest)
{
   int sizeIdx;
   int headerByteCount, outputLength, symbolRemaining;

   if(stream->status == DmtxStatusComplete)
      return;

   if(!StreamInputHasNext(stream))
   {
      headerByteCount = stream->outputChainWordCount - stream->outputChainValueCount;
      assert(headerByteCount == 1 || headerByteCount == 2);

      /* Check for special case where every last symbol word is used */
      if(headerByteCount == 2)
      {
         /* Find symbol size as if headerByteCount was only 1 */
         outputLength = stream->output->length - 1;
         sizeIdx = FindSymbolSize(outputLength, sizeIdxRequest); /* No CHKSIZE */
         if(sizeIdx != DmtxUndefined)
         {
            symbolRemaining = GetRemainingSymbolCapacity(outputLength, sizeIdx);

            if(symbolRemaining == 0)
            {
               /* Perfect fit -- complete encoding */
               UpdateBase256ChainHeader(stream, sizeIdx); CHKERR;
               StreamMarkComplete(stream, sizeIdx);
               return;
            }
         }
      }

      /* Normal case */
      sizeIdx = FindSymbolSize(stream->output->length, sizeIdxRequest); CHKSIZE;
      EncodeChangeScheme(stream, DmtxSchemeAscii, DmtxUnlatchImplicit);
      PadRemainingInAscii(stream, sizeIdx);
      StreamMarkComplete(stream, sizeIdx);
   }
}

/**
 *
 *
 */
static void
UpdateBase256ChainHeader(DmtxEncodeStream *stream, int perfectSizeIdx)
{
   int headerIndex;
   int outputLength;
   int headerByteCount;
   int symbolDataWords;
   DmtxBoolean perfectFit;
   DmtxByte headerValue0;
   DmtxByte headerValue1;

   outputLength = stream->outputChainValueCount;
   headerIndex = stream->output->length - stream->outputChainWordCount;
   headerByteCount = stream->outputChainWordCount - stream->outputChainValueCount;
   perfectFit = (perfectSizeIdx == DmtxUndefined) ? DmtxFalse : DmtxTrue;

   /*
    * If requested perfect fit verify symbol capacity against final length
    */

   if(perfectFit)
   {
      symbolDataWords = dmtxGetSymbolAttribute(DmtxSymAttribSymbolDataWords, perfectSizeIdx);
      if(symbolDataWords != stream->output->length - 1)
      {
         StreamMarkFatal(stream, DmtxErrorUnknown);
         return;
      }
   }

   /*
    * Adjust header to hold correct number of bytes, not worrying about the
    * values held there until below. Note: Header bytes are not considered
    * scheme "values" so we can insert or remove them without updating the
    * outputChainValueCount.
    */

   if(headerByteCount == 0 && stream->outputChainWordCount == 0)
   {
      /* No output words written yet -- insert single header byte */
      StreamOutputChainAppend(stream, 0); CHKERR;
      headerByteCount++;
   }
   else if(!perfectFit && headerByteCount == 1 && outputLength > 249)
   {
      /* Beyond 249 bytes requires a second header byte */
      Base256OutputChainInsertFirst(stream); CHKERR;
      headerByteCount++;
   }
   else if(perfectFit && headerByteCount == 2)
   {
      /* Encoding to exact end of symbol only requires single byte */
      Base256OutputChainRemoveFirst(stream); CHKERR;
      headerByteCount--;
   }

   /*
    * Encode header byte(s) with current length
    */

   if(!perfectFit && headerByteCount == 1 && outputLength <= 249)
   {
      /* Normal condition for chain length < 250 bytes */
      headerValue0 = Randomize255State(outputLength, headerIndex + 1);
      StreamOutputSet(stream, headerIndex, headerValue0); CHKERR;
   }
   else if(!perfectFit && headerByteCount == 2 && outputLength > 249)
   {
      /* Normal condition for chain length >= 250 bytes */
      headerValue0 = Randomize255State(outputLength/250 + 249, headerIndex + 1);
      StreamOutputSet(stream, headerIndex, headerValue0); CHKERR;

      headerValue1 = Randomize255State(outputLength%250, headerIndex + 2);
      StreamOutputSet(stream, headerIndex + 1, headerValue1); CHKERR;
   }
   else if(perfectFit && headerByteCount == 1)
   {
      /* Special condition when Base 256 stays in effect to end of symbol */
      headerValue0 = Randomize255State(0, headerIndex + 1); /* XXX replace magic value 0? */
      StreamOutputSet(stream, headerIndex, headerValue0); CHKERR;
   }
   else
   {
      StreamMarkFatal(stream, DmtxErrorUnknown);
      return;
   }
}

/**
 * insert element at beginning of chain, shifting all following elements forward by one
 * used for binary length changes
 */
static void
Base256OutputChainInsertFirst(DmtxEncodeStream *stream)
{
   DmtxByte value;
   DmtxPassFail passFail;
   int i, chainStart;

   chainStart = stream->output->length - stream->outputChainWordCount;
   dmtxByteListPush(stream->output, 0, &passFail);
   if(passFail == DmtxPass)
   {
      for(i = stream->output->length - 1; i > chainStart; i--)
      {
         value = UnRandomize255State(stream->output->b[i-1], i);
         stream->output->b[i] = Randomize255State(value, i + 1);
      }

      stream->outputChainWordCount++;
   }
   else
   {
      StreamMarkFatal(stream, DmtxErrorUnknown);
   }
}

/**
 * remove first element from chain, shifting all following elements back by one
 * used for binary length changes end condition
 */
static void
Base256OutputChainRemoveFirst(DmtxEncodeStream *stream)
{
   DmtxByte value;
   DmtxPassFail passFail;
   int i, chainStart;

   chainStart = stream->output->length - stream->outputChainWordCount;

   for(i = chainStart; i < stream->output->length - 1; i++)
   {
      value = UnRandomize255State(stream->output->b[i+1], i+2);
      stream->output->b[i] = Randomize255State(value, i + 1);
   }

   dmtxByteListPop(stream->output, &passFail);
   if(passFail == DmtxPass)
      stream->outputChainWordCount--;
   else
      StreamMarkFatal(stream, DmtxErrorUnknown);
}

/**
 * \brief  Randomize 255 state
 * \param  value
 * \param  position
 * \return Randomized value
 */
static DmtxByte
Randomize255State(DmtxByte value, int position)
{
   int pseudoRandom, tmp;

   pseudoRandom = ((149 * position) % 255) + 1;
   tmp = value + pseudoRandom;

   return (tmp <= 255) ? tmp : tmp - 256;
}

/**
 * \brief  Unrandomize 255 state
 * \param  value
 * \param  idx
 * \return Unrandomized value
 */
static unsigned char
UnRandomize255State(unsigned char value, int idx)
{
   int pseudoRandom;
   int tmp;

   pseudoRandom = ((149 * idx) % 255) + 1;
   tmp = value - pseudoRandom;
   if(tmp < 0)
      tmp += 256;

   assert(tmp >= 0 && tmp < 256);

   return (unsigned char)tmp;
}