/* Copyright (C) 1996 Aladdin Enterprises.  All rights reserved.
  
  This file is part of Aladdin Ghostscript.
  
  Aladdin Ghostscript is distributed with NO WARRANTY OF ANY KIND.  No author
  or distributor accepts any responsibility for the consequences of using it,
  or for whether it serves any particular purpose or works at all, unless he
  or she says so in writing.  Refer to the Aladdin Ghostscript Free Public
  License (the "License") for full details.
  
  Every copy of Aladdin Ghostscript must include a copy of the License,
  normally in a plain ASCII text file named PUBLIC.  The License grants you
  the right to copy, modify and redistribute Aladdin Ghostscript, but only
  under certain conditions described in the License.  Among other things, the
  License requires that the copyright notice and this notice be preserved on
  all copies.
*/

/* spngp.c */
/* PNG pixel prediction filters */
#include "memory_.h"
#include "strimpl.h"
#include "spngpx.h"

/* ------ PNGPredictorEncode/Decode ------ */

private_st_PNGP_state();

#define ss ((stream_PNGP_state *)st)
#define ss_const ((const stream_PNGP_state *)st_const)

/* Define values for case dispatch. */
#define cNone 10
#define cSub 11
#define cUp 12
#define cAverage 13
#define cPaeth 14
#define cOptimum 15
#define cEncode -10
#define cDecode -4
private const byte pngp_case_needs_prev[] = { 0, 0, 1, 1, 1, 1 };

/* Set defaults */
private void
s_PNGP_set_defaults(stream_state *st)
{	s_PNGP_set_defaults_inline(ss);
}

/* Common (re)initialization. */
private int
s_PNGP_reinit(stream_state *st)
{	if ( ss->prev_row != 0 )
	  memset(ss->prev_row + ss->bpp, 0, ss->row_count);
	ss->row_left = 0;
	return 0;
}

/* Initialize PNGPredictorEncode filter. */
private int
s_pngp_init(stream_state *st, bool need_prev)
{	int bits_per_pixel = ss->Colors * ss->BitsPerComponent;
	long bits_per_row = (long)bits_per_pixel * ss->Columns;
	byte *prev_row = 0;

#if arch_sizeof_long > arch_sizeof_int
	if ( bits_per_row > max_uint * 7L )
	  return ERRC;		/****** WRONG ******/
#endif
	ss->row_count = (uint)((bits_per_row + 7) >> 3);
	ss->end_mask = (1 << (-bits_per_row & 7)) - 1;
	ss->bpp = (bits_per_pixel + 7) >> 3;
	if ( need_prev )
	  { prev_row = gs_alloc_bytes(st->memory, ss->bpp + ss->row_count,
				      "PNGPredictor prev row");
	    if ( prev_row == 0 )
	      return ERRC;	/****** WRONG ******/
	    memset(prev_row, 0, ss->bpp);
	  }
	ss->prev_row = prev_row;
	/* case_index is only preset for encoding */
	return s_PNGP_reinit(st);
}

/* Initialize PNGPredictorEncode filter. */
private int
s_PNGPE_init(stream_state *st)
{	return s_pngp_init(st, pngp_case_needs_prev[ss->Predictor - cNone]);
}

/* Initialize PNGPredictorDecode filter. */
private int
s_PNGPD_init(stream_state *st)
{	return s_pngp_init(st, true);
}

/*
 * Process a partial buffer.  We pass in current and previous pointers
 * to both the current and preceding scan line.  Note that dprev is
 * p - bpp for encoding, q - bpp for decoding; similarly, the 'up' row
 * is the raw data for encoding, the filtered data for decoding.
 * Note also that the case_index cannot be cOptimum.
 */
private int
paeth_predictor(int a, int b, int c)
{
#define any_abs(u) ((u) < 0 ? -(u) : (u))
	int px = a + b - c;
	int pa = any_abs(px - a), pb = any_abs(px - b), pc = any_abs(px - c);
	return (pa <= pb && pa <= pc ? a : pb <= pc ? b : c);
#undef any_abs
}
private void
s_pngp_process(stream_state *st, stream_cursor_write *pw,
  const byte *dprev, stream_cursor_read *pr,
  const byte *upprev, const byte *up, uint count)
{	byte *q = pw->ptr + 1;
	const byte *p = pr->ptr + 1;

	pr->ptr += count;
	pw->ptr += count;
	ss->row_left -= count;
	switch ( ss->case_index )
	  {
	  case cEncode + cNone:
	  case cDecode + cNone:
		memcpy(q, p, count);
		break;
	  case cEncode + cSub:
		for ( ; count; ++q, ++dprev, ++p, --count )
		  *q = (byte)(*p - *dprev);
		break;
	  case cDecode + cSub:
		for ( ; count; ++q, ++dprev, ++p, --count )
		  *q = (byte)(*p + *dprev);
		break;
	  case cEncode + cUp:
		for ( ; count; ++q, ++up, ++p, --count )
		  *q = (byte)(*p - *up);
		break;
	  case cDecode + cUp:
		for ( ; count; ++q, ++up, ++p, --count )
		  *q = (byte)(*p + *up);
		break;
	  case cEncode + cAverage:
		for ( ; count; ++q, ++dprev, ++up, ++p, --count )
		  *q = (byte)(*p - arith_rshift_1((int)*dprev + (int)*up));
		break;
	  case cDecode + cAverage:
		for ( ; count; ++q, ++dprev, ++up, ++p, --count )
		  *q = (byte)(*p + arith_rshift_1((int)*dprev + (int)*up));
		break;
	  case cEncode + cPaeth:
		for ( ; count; ++q, ++dprev, ++up, ++upprev, ++p, --count )
		  *q = (byte)(*p - paeth_predictor(*dprev, *up, *upprev));
		break;
	  case cDecode + cPaeth:
		for ( ; count; ++q, ++dprev, ++up, ++upprev, ++p, --count )
		  *q = (byte)(*p + paeth_predictor(*dprev, *up, *upprev));
		break;
	  }
}

/* Calculate the number of bytes for the next processing step, */
/* the min of (input data, output data, remaining row length). */
private uint near
s_pngp_count(const stream_state *st_const, const stream_cursor_read *pr,
  const stream_cursor_write *pw)
{	uint rcount = pr->limit - pr->ptr;
	uint wcount = pw->limit - pw->ptr;
	uint row_left = ss_const->row_left;

	if ( rcount < row_left )
	  row_left = rcount;
	if ( wcount < row_left )
	  row_left = wcount;
	return row_left;
}

/*
 * Encode a buffer.  Let N = ss->row_count, P = N - ss->row_left,
 * and B = ss->bpp.  Consider that bytes [-B .. -1] of every row are zero.
 * Then:
 *	prev_row[0 .. P - 1] contain bytes -B .. P - B - 1
 *	  of the current input row.
 *	ss->prev[0 .. B - 1] contain bytes P - B .. P - 1
 *	  of the current input row.
 *	prev_row[P .. N + B - 1] contain bytes P - B .. N - 1
 *	  of the previous input row.
 */
private int
optimum_predictor(const stream_state *st, const stream_cursor_read *pr)
{	return cSub;
}
private int
s_PNGPE_process(stream_state *st, stream_cursor_read *pr,
  stream_cursor_write *pw, bool last)
{	int bpp = ss->bpp;
	int code = 0;
	while ( pr->ptr < pr->limit )
	  {	uint count;
		if ( ss->row_left == 0 )
		  { /* Beginning of row, write algorithm byte. */
		    int predictor;
		    if ( pw->ptr >= pw->limit )
		      { code = 1;
			break;
		      }
		    predictor =
		      (ss->Predictor == cOptimum ?
		       optimum_predictor(st, pr) :
		       ss->Predictor);
		    *++(pw->ptr) = (byte)predictor - cNone;
		    ss->case_index = predictor + cEncode;
		    ss->row_left = ss->row_count;
		    memset(ss->prev, 0, bpp);
		    continue;
		  }
		count = s_pngp_count(st, pr, pw);
		if ( count == 0 )
		  { /* We know we have input, so output must be full. */
		    code = 1;
		    break;
		  }
		{ byte *up = ss->prev_row + bpp + ss->row_count - ss->row_left;
		  uint n = min(count, bpp);

		  /* Process bytes whose predecessors are in prev. */
		  s_pngp_process(st, pw, ss->prev, pr, up - bpp, up, n);
		  if ( ss->prev_row )
		    memcpy(up - bpp, ss->prev, n);
		  if ( n < bpp )
		    { /* We didn't have enough data to use up all of prev. */
		      /* Shift more data into prev and exit. */
		      int prev_left = bpp - n;
		      memmove(ss->prev, ss->prev + n, prev_left);
		      memcpy(ss->prev + prev_left, pr->ptr - (n - 1), n);
		      break;
		    }
		  /* Process bytes whose predecessors are in the input. */
		  /* We know we have at least bpp input and output bytes, */
		  /* and that n = bpp. */
		  count -= bpp;
		  s_pngp_process(st, pw, pr->ptr - (bpp - 1), pr,
				 up, up + bpp, count);
		  memcpy(ss->prev, pr->ptr - (bpp - 1), bpp);
		  if ( ss->prev_row )
		    { memcpy(up, pr->ptr - (bpp + count - 1), count);
		      if ( ss->row_left == 0 )
			memcpy(up + count, ss->prev, bpp);
		    }
		}
	  }
	return code;
}

/*
 * Decode a buffer.  Let N = ss->row_count, P = N - ss->row_left,
 * and B = ss->bpp.  Consider that bytes [-B .. -1] of every row are zero.
 * Then:
 *	prev_row[0 .. P - 1] contain bytes -B .. P - B - 1
 *	  of the current output row.
 *	ss->prev[0 .. B - 1] contain bytes P - B .. P - 1
 *	  of the current output row.
 *	prev_row[P .. N + B - 1] contain bytes P - B .. N - 1
 *	  of the previous output row.
 */
private int
s_PNGPD_process(stream_state *st, stream_cursor_read *pr,
  stream_cursor_write *pw, bool last)
{	int bpp = ss->bpp;
	int code = 0;
	while ( pr->ptr < pr->limit )
	  {	uint count;
		if ( ss->row_left == 0 )
		  { /* Beginning of row, read algorithm byte. */
		    int predictor = pr->ptr[1];
		    if ( predictor >= cOptimum - cNone )
		      { code = ERRC;
			break;
		      }
		    pr->ptr++;
		    ss->case_index = predictor + cNone + cDecode;
		    ss->row_left = ss->row_count;
		    memset(ss->prev, 0, bpp);
		    continue;
		  }
		count = s_pngp_count(st, pr, pw);
		if ( count == 0 )
		  { /* We know we have input, so output must be full. */
		    code = 1;
		    break;
		  }
		{ byte *up = ss->prev_row + bpp + ss->row_count - ss->row_left;
		  uint n = min(count, bpp);

		  /* Process bytes whose predecessors are in prev. */
		  s_pngp_process(st, pw, ss->prev, pr, up - bpp, up, n);
		  if ( ss->prev_row )
		    memcpy(up - bpp, ss->prev, n);
		  if ( n < bpp )
		    { /* We didn't have enough data to use up all of prev. */
		      /* Shift more data into prev and exit. */
		      int prev_left = bpp - n;
		      memmove(ss->prev, ss->prev + n, prev_left);
		      memcpy(ss->prev + prev_left, pw->ptr - (n - 1), n);
		      break;
		    }
		  /* Process bytes whose predecessors are in the output. */
		  /* We know we have at least bpp input and output bytes, */
		  /* and that n = bpp. */
		  count -= bpp;
		  s_pngp_process(st, pw, pw->ptr - (bpp - 1), pr,
				 up, up + bpp, count);
		  memcpy(ss->prev, pw->ptr - (bpp - 1), bpp);
		  if ( ss->prev_row )
		    { memcpy(up, pw->ptr - (bpp + count - 1), count);
		      if ( ss->row_left == 0 )
			memcpy(up + count, ss->prev, bpp);
		    }
		}
	  }
	return code;
}

/* Stream templates */
const stream_template s_PNGPE_template =
{	&st_PNGP_state, s_PNGPE_init, s_PNGPE_process, 1, 1, 0/*NULL*/,
	s_PNGP_set_defaults, s_PNGP_reinit
};
const stream_template s_PNGPD_template =
{	&st_PNGP_state, s_PNGPD_init, s_PNGPD_process, 1, 1, 0/*NULL*/,
	s_PNGP_set_defaults, s_PNGP_reinit
};
