/* Copyright (C) 2001-2012 Artifex Software, Inc.
   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.

   Refer to licensing information at http://www.artifex.com or contact
   Artifex Software, Inc.,  7 Mt. Lassen Drive - Suite A-134, San Rafael,
   CA  94903, U.S.A., +1(415)492-9861, for further information.
*/


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

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

private_st_MTF_state();

/* Initialize */
static 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 */
static 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 */
static 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
};