/* Portions Copyright (C) 2001 artofcode LLC.
   Portions Copyright (C) 1996, 2001 Artifex Software Inc.
   Portions Copyright (C) 1988, 2000 Aladdin Enterprises.
   This software is based in part on the work of the Independent JPEG Group.
   All Rights Reserved.

   This software is distributed under license and may not be copied, modified
   or distributed except as expressly authorized under the terms of that
   license.  Refer to licensing information at http://www.artifex.com/ or
   contact Artifex Software, Inc., 101 Lucas Valley Road #110,
   San Rafael, CA  94903, (415)492-9861, for further information. */

/*$RCSfile: smtf.c,v $ $Revision: 1.9 $ */
/* MoveToFront filters */
#include "stdio_.h"
#include "strimpl.h"
#include "smtf.h"

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

private_st_MTF_state();

/* Initialize */
private int
s_MTF_init(stream_state * st)
{
    stream_MTF_state *const ss = (stream_MTF_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(const gs_memory_t *mem, stream_state * st, stream_cursor_read * pr,
	       stream_cursor_write * pw, bool last)
{
    stream_MTF_state *const ss = (stream_MTF_state *) st;
    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(const gs_memory_t *mem, stream_state * st, stream_cursor_read * pr,
	       stream_cursor_write * pw, bool last)
{
    stream_MTF_state *const ss = (stream_MTF_state *) st;
    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) |
			    ((ulong) 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
};
