ref: 27ff6876d02ff5d326d6ee13d2466a6e4a3e0925
dir: /sys/src/cmd/gs/src/smtf.c/
/* Copyright (C) 1995, 1996, 1998 Aladdin Enterprises. All rights reserved.
This software is provided AS-IS with no warranty, either express or
implied.
This software is distributed under license and may not be copied,
modified or distributed except as expressly authorized under the terms
of the license contained in the file LICENSE in this distribution.
For more information about licensing, please refer to
http://www.ghostscript.com/licensing/. For information on
commercial licensing, go to http://www.artifex.com/licensing/ or
contact Artifex Software, Inc., 101 Lucas Valley Road #110,
San Rafael, CA 94903, U.S.A., +1(415)492-9861.
*/
/* $Id: smtf.c,v 1.4 2002/02/21 22:24:54 giles Exp $ */
/* 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(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(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
};