/* Copyright (C) 1995, 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.
*/

/* smtf.c */
/* MoveToFront filters */
#include "stdio_.h"
#include "strimpl.h"
#include "smtf.h"

/* ------ MoveToFrontEncode/Decode ------ */

private_st_MTF_state();

#define ss ((stream_MTF_state *)st)

/* Initialize */
private int
s_MTF_init(stream_state *st)
{	int i;
	for ( i = 0; i < 256; i++ )
	  ss->prev.b[i] = (byte)i;
	return 0;
}

/* Encode a buffer */
private int
s_MTFE_process(stream_state *st, stream_cursor_read *pr,
  stream_cursor_write *pw, bool last)
{	register const byte *p = pr->ptr;
	register byte *q = pw->ptr;
	const byte *rlimit = pr->limit;
	uint count = rlimit - p;
	uint wcount = pw->limit - q;
	int status =
		(count < wcount ? 0 :
		 (rlimit = p + wcount, 1));
	while ( p < rlimit )
	{	byte b = *++p;
		int i;
		byte prev = b, repl;
		for ( i = 0; (repl = ss->prev.b[i]) != b; i++ )
		  ss->prev.b[i] = prev, prev = repl;
		ss->prev.b[i] = prev;
		*++q = (byte)i;
	}
	pr->ptr = p;
	pw->ptr = q;
	return status;
}

/* Stream template */
const stream_template s_MTFE_template =
{	&st_MTF_state, s_MTF_init, s_MTFE_process, 1, 1
};

/* Decode a buffer */
private int
s_MTFD_process(stream_state *st, stream_cursor_read *pr,
  stream_cursor_write *pw, bool last)
{	register const byte *p = pr->ptr;
	register byte *q = pw->ptr;
	const byte *rlimit = pr->limit;
	uint count = rlimit - p;
	uint wcount = pw->limit - q;
	int status = (count <= wcount ? 0 : (rlimit = p + wcount, 1));
	/* Cache the first few entries in local variables. */
	byte
	  v0 = ss->prev.b[0], v1 = ss->prev.b[1],
	  v2 = ss->prev.b[2], v3 = ss->prev.b[3];
	while ( p < rlimit )
	{	byte first;
		/* Zeros far outnumber all other bytes in the BWBS */
		/* code; check for them first. */
		if ( *++p == 0 )
		  {	*++q = v0;
			continue;
		  }
		switch ( *p )
		{
		default:
		  {	uint b = *p;
			byte *bp = &ss->prev.b[b];
			*++q = first = *bp;
#if arch_sizeof_long == 4
			ss->prev.b[3] = v3;
#endif
			/* Move trailing entries individually. */
			for ( ; ; bp--, b-- )
			  {	*bp = bp[-1];
				if ( !(b & (sizeof(long) - 1)) )
				  break;
			  }
			/* Move in long-size chunks. */
			for ( ; (b -= sizeof(long)) != 0; )
			  {	bp -= sizeof(long);
#if arch_is_big_endian
				*(ulong *)bp =
				  (*(ulong *)bp >> 8) |
				    (bp[-1] << ((sizeof(long) - 1) * 8));
#else
				*(ulong *)bp = (*(ulong *)bp << 8) | bp[-1];
#endif
			  }
		  }
#if arch_sizeof_long > 4	/* better be 8! */
			goto m7;
		case 7:
			*++q = first = ss->prev.b[7];
m7:			ss->prev.b[7] = ss->prev.b[6];
			goto m6;
		case 6:
			*++q = first = ss->prev.b[6];
m6:			ss->prev.b[6] = ss->prev.b[5];
			goto m5;
		case 5:
			*++q = first = ss->prev.b[5];
m5:			ss->prev.b[5] = ss->prev.b[4];
			goto m4;
		case 4:
			*++q = first = ss->prev.b[4];
m4:			ss->prev.b[4] = v3;
#endif
			goto m3;
		case 3:
			*++q = first = v3;
m3:			v3 = v2, v2 = v1, v1 = v0, v0 = first;
			break;
		case 2:
			*++q = first = v2;
			v2 = v1, v1 = v0, v0 = first;
			break;
		case 1:
			*++q = first = v1;
			v1 = v0, v0 = first;
			break;
		}
	}
	ss->prev.b[0] = v0;  ss->prev.b[1] = v1;
	ss->prev.b[2] = v2;  ss->prev.b[3] = v3;
	pr->ptr = p;
	pw->ptr = q;
	return status;
}

/* Stream template */
const stream_template s_MTFD_template =
{	&st_MTF_state, s_MTF_init, s_MTFD_process, 1, 1,
	NULL, NULL, s_MTF_init
};

#undef ss
