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%%	options

copyright owner	=	Dirk Krause
copyright year	=	2015-xxxx
license		=	bsd


%%	header

/**	@file	dk4rld.h	Run-length decoder.

Use dk4rld_init() to initialize the decoder before feeding data to it.

Feed the encoded data into the decoder byte by byte, use the
dk4rld_add() function.
If the function returns DK4_EDSTM_ACCEPT, the input was successfully stored
into the internal data structures, not need for further action.
If the function returns DK4_EDSTM_FINISHED, an output secquence was
completed, either a run or a literal byte sequence. Use dk4rld_output()
to retrieve output data.
If the dk4rld_add function returns DK4_EDSTM_STOP, an end of data
(EOD) marker was found; do not feed further bytes into the decoder.

After feeding all input bytes into the decoder, use dk4rld_finish() to check
syntax. If the function returns DK4_EDSTM_ERROR, the input data stream
was not properly run-length encoded.
*/

#include "dk4error.h"

/**	Run length decoder.
*/
typedef struct {
  unsigned char		ob[128];	/**< Output buffer. */
  size_t		oused;		/**< Number of used bytes in ob. */
  size_t		ll;		/**< Number of expected bytes. */
  int			st;		/**< Current state. */
} dk4_rl_dec_t;


#ifdef __cplusplus
extern "C" {
#endif

/**	Initialize decoder.
	@param	dec	Decoder to initialize.
	@param	erp	Error report, may be NULL.

	Error codes:
	- DK4_E_INVALID_ARGUMENTS	if enc is NULL.
*/
void
dk4rld_init(dk4_rl_dec_t *dec, dk4_er_t *erp);

/**	Add one encoded byte to decoder.
	@param	dec	Decoder.
	@param	inbyte	Byte to process.
	@param	erp	Error report, may be NULL.
	@return	Action to take, one from:
	- DK4_EDSTM_ACCEPT<br>
	  if the byte was successfully added
	  to the internal data structures, no further action necessary.
	- DK4_EDSTM_FINISHED<br>
	  if output is available, use dk4rld_output() to retrieve output.
	- DK4_EDSTM_STOP<br>
	  if an EOD marker was detected. Do not feed further bytes
	  to the decoder.
	- DK4_EDSTM_ERROR<br>
	  if an error occured.

	Error codes:
	- DK4_E_INVALID_ARGUMENTS	if enc is NULL.
*/
int
dk4rld_add(dk4_rl_dec_t *dec, unsigned char inbyte, dk4_er_t *erp);

/**	Finish decoding.
	@param	dec	Decoder.
	@param	erp	Error report, may be NULL.
	@return	Action to take, one from:
	- DK4_EDSTM_ACCEPT<br>
	  if no remaining data is stored in the decoder, no further
	  action necessary.
	- DK4_EDSTM_FINISHED<br>
	  if output is available, use dk4rld_output() to retrieve output.
	- DK4_EDSTM_ERROR<br>
	  if an error occured.

	Error codes:
	- DK4_E_INVALID_ARGUMENTS<br>
	  if enc is NULL.
	- DK4_E_SYNTAX<br>
	  if data indicated by the run-length byte or literally-length
	  byte is missing.
*/
int
dk4rld_finish(dk4_rl_dec_t *dec, dk4_er_t *erp);

/**	Retrieve decoder output.
	@param	dptr	Address of pointer to set to decoder output,
			should be initialized to NULL.
	@param	szptr	Address of variable to receive buffer size,
			should be initialized to 0.
	@param	dec	Decoder.
	@param	erp	Error report, may be NULL.
	@return	1 if data is available, 0 otherwise.

	Error codes:
	- DK4_E_INVALID_ARGUMENTS	if enc is NULL.
*/
int
dk4rld_output(
  const unsigned char **dptr, size_t *szptr, dk4_rl_dec_t *dec, dk4_er_t *erp
);

#ifdef __cplusplus
}
#endif

%%	module

#include "dk4rld.h"
#include "dk4edstm.h"
#include "dk4mem.h"



$!trace-include



/**	Decoder states.
*/
enum {
				/**	Start state, exepect run length
					or literal data length.
				*/
  RLD_ST_EXPECT_KEY_BYTE	=	0,

				/**	Expect byte value for run.
				*/
  RLD_ST_EXPECT_RUN_BYTE ,

				/**	Expect literal byte.
				*/
  RLD_ST_EXPECT_LITERAL_BYTE ,

				/**	No further input accepted as
					EOD marker was found.
				*/
  RLD_ST_EOD_FOUND 
};



void
dk4rld_init(dk4_rl_dec_t *dec, dk4_er_t *erp)
{
  $? "+ dk4rld_init"
  if (NULL != dec) {
    DK4_MEMRES(dec, sizeof(dk4_rl_dec_t));
    dec->oused = 0;
    dec->ll    = 0;
    dec->st    = RLD_ST_EXPECT_KEY_BYTE;
  } else {
    dk4error_set_simple_error_code(erp, DK4_E_INVALID_ARGUMENTS);
  } $? "- dk4rld_init"
}



int
dk4rld_add(dk4_rl_dec_t *dec, unsigned char inbyte, dk4_er_t *erp)
{
  int		 back	=	DK4_EDSTM_ERROR;
  $? "+ dk4rld_add"
  if (NULL != dec) {
    switch (dec->st) {
      case RLD_ST_EXPECT_KEY_BYTE : {
        if ((unsigned char)128 > inbyte) {
	  /*
	  	Literal byte sequence
	  */
	  dec->st = RLD_ST_EXPECT_LITERAL_BYTE;
	  dec->ll = (size_t)inbyte + 1;
	  back    = DK4_EDSTM_ACCEPT;
	} else {
	  if ((unsigned char)128 < inbyte) {
	    /*
	    	Run of equal bytes
	    */
	    dec->st = RLD_ST_EXPECT_RUN_BYTE;
	    dec->ll = (size_t)257 - (size_t)inbyte;
	    back    = DK4_EDSTM_ACCEPT;
	  } else {
	    /*
	    	EOD marker found
	    */
	    dec->st = RLD_ST_EOD_FOUND;
	    back    = DK4_EDSTM_STOP;
	  }
	}
      } break;
      case RLD_ST_EXPECT_RUN_BYTE : {
        dk4mem_set(&(dec->ob[0]), dec->ll, inbyte, NULL);
	dec->oused = dec->ll;
	dec->st = RLD_ST_EXPECT_KEY_BYTE;
	back = DK4_EDSTM_FINISHED;
      } break;
      case RLD_ST_EXPECT_LITERAL_BYTE : {
        dec->ob[0] = inbyte;
	dec->oused = 1;
	dec->ll -= 1;
	if (0 == dec->ll) {
	  dec->st = RLD_ST_EXPECT_KEY_BYTE;
	}
	back = DK4_EDSTM_FINISHED;
      } break;
      default : {
        dk4error_set_simple_error_code(erp, DK4_E_SYNTAX);
      } break;
    }
  } else {
    dk4error_set_simple_error_code(erp, DK4_E_INVALID_ARGUMENTS);
  } $? "- dk4rld_add %d", back
  return back;
}



int
dk4rld_finish(dk4_rl_dec_t *dec, dk4_er_t *erp)
{
  int		 back	=	DK4_EDSTM_ERROR;
  $? "+ dk4rld_finish"
  if (NULL != dec) {
    switch (dec->st) {
      case RLD_ST_EXPECT_KEY_BYTE : case RLD_ST_EOD_FOUND : {
        back = DK4_EDSTM_ACCEPT;
      } break;
      default : {
        dk4error_set_simple_error_code(erp, DK4_E_SYNTAX);
      } break;
    }
  } else {
    dk4error_set_simple_error_code(erp, DK4_E_INVALID_ARGUMENTS);
  } $? "- dk4rld_finish %d", back
  return back;
}



int
dk4rld_output(
  const unsigned char **dptr, size_t *szptr, dk4_rl_dec_t *dec, dk4_er_t *erp
)
{
  int		 back	=	0;
  $? "+ dk4rld_output"
  if (NULL != dec) {
    if (0 < dec->oused) {
      *dptr = &(dec->ob[0]);
      *szptr = dec->oused;
      back = 1;
    } else {
      *dptr = NULL;
      *szptr = 0;
    }
  } else {
    dk4error_set_simple_error_code(erp, DK4_E_INVALID_ARGUMENTS);
  } $? "- dk4rld_output %d", back
  return back;
}