compr_rubin.c

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    1 /*
    2  * JFFS2 -- Journalling Flash File System, Version 2.
    3  *
    4  * Copyright (C) 2001 Red Hat, Inc.
    5  *
    6  * Created by Arjan van de Ven <arjanv@redhat.com>
    7  *
    8  * The original JFFS, from which the design for JFFS2 was derived,
    9  * was designed and implemented by Axis Communications AB.
   10  *
   11  * The contents of this file are subject to the Red Hat eCos Public
   12  * License Version 1.1 (the "Licence"); you may not use this file
   13  * except in compliance with the Licence.  You may obtain a copy of
   14  * the Licence at http://www.redhat.com/
   15  *
   16  * Software distributed under the Licence is distributed on an "AS IS"
   17  * basis, WITHOUT WARRANTY OF ANY KIND, either express or implied.
   18  * See the Licence for the specific language governing rights and
   19  * limitations under the Licence.
   20  *
   21  * The Original Code is JFFS2 - Journalling Flash File System, version 2
   22  *
   23  * Alternatively, the contents of this file may be used under the
   24  * terms of the GNU General Public License version 2 (the "GPL"), in
   25  * which case the provisions of the GPL are applicable instead of the
   26  * above.  If you wish to allow the use of your version of this file
   27  * only under the terms of the GPL and not to allow others to use your
   28  * version of this file under the RHEPL, indicate your decision by
   29  * deleting the provisions above and replace them with the notice and
   30  * other provisions required by the GPL.  If you do not delete the
   31  * provisions above, a recipient may use your version of this file
   32  * under either the RHEPL or the GPL.
   33  *
   34  * $Id: compr_rubin.c,v 1.13 2001/09/23 10:06:05 rmk Exp $
   35  *
   36  */
   37 
   38  
   39 #include <linux/string.h>
   40 #include <linux/types.h>
   41 #include "compr_rubin.h"
   42 #include "histo_mips.h"
   43 
   44 
   45 
   46 void init_rubin(struct rubin_state *rs, int div, int *bits)
   47 {       
   48         int c;
   49 
   50         rs->q = 0;
   51         rs->p = (long) (2 * UPPER_BIT_RUBIN);
   52         rs->bit_number = (long) 0;
   53         rs->bit_divider = div;
   54         for (c=0; c<8; c++)
   55                 rs->bits[c] = bits[c];
   56 }
   57 
   58 
   59 int encode(struct rubin_state *rs, long A, long B, int symbol)
   60 {
   61 
   62         long i0, i1;
   63         int ret;
   64 
   65         while ((rs->q >= UPPER_BIT_RUBIN) || ((rs->p + rs->q) <= UPPER_BIT_RUBIN)) {
   66                 rs->bit_number++;
   67                 
   68                 ret = pushbit(&rs->pp, (rs->q & UPPER_BIT_RUBIN) ? 1 : 0, 0);
   69                 if (ret)
   70                         return ret;
   71                 rs->q &= LOWER_BITS_RUBIN;
   72                 rs->q <<= 1;
   73                 rs->p <<= 1;
   74         }
   75         i0 = A * rs->p / (A + B);
   76         if (i0 <= 0) {
   77                 i0 = 1;
   78         }
   79         if (i0 >= rs->p) {
   80                 i0 = rs->p - 1;
   81         }
   82         i1 = rs->p - i0;
   83 
   84         if (symbol == 0)
   85                 rs->p = i0;
   86         else {
   87                 rs->p = i1;
   88                 rs->q += i0;
   89         }
   90         return 0;
   91 }
   92 
   93 
   94 void end_rubin(struct rubin_state *rs)
   95 {                               
   96 
   97         int i;
   98 
   99         for (i = 0; i < RUBIN_REG_SIZE; i++) {
  100                 pushbit(&rs->pp, (UPPER_BIT_RUBIN & rs->q) ? 1 : 0, 1);
  101                 rs->q &= LOWER_BITS_RUBIN;
  102                 rs->q <<= 1;
  103         }
  104 }
  105 
  106 
  107 void init_decode(struct rubin_state *rs, int div, int *bits)
  108 {
  109         init_rubin(rs, div, bits);              
  110 
  111         /* behalve lower */
  112         rs->rec_q = 0;
  113 
  114         for (rs->bit_number = 0; rs->bit_number++ < RUBIN_REG_SIZE; rs->rec_q = rs->rec_q * 2 + (long) (pullbit(&rs->pp)))
  115                 ;
  116 }
  117 
  118 static void __do_decode(struct rubin_state *rs, unsigned long p, unsigned long q)
  119 {
  120         register unsigned long lower_bits_rubin = LOWER_BITS_RUBIN;
  121         unsigned long rec_q;
  122         int c, bits = 0;
  123 
  124         /*
  125          * First, work out how many bits we need from the input stream.
  126          * Note that we have already done the initial check on this
  127          * loop prior to calling this function.
  128          */
  129         do {
  130                 bits++;
  131                 q &= lower_bits_rubin;
  132                 q <<= 1;
  133                 p <<= 1;
  134         } while ((q >= UPPER_BIT_RUBIN) || ((p + q) <= UPPER_BIT_RUBIN));
  135 
  136         rs->p = p;
  137         rs->q = q;
  138 
  139         rs->bit_number += bits;
  140 
  141         /*
  142          * Now get the bits.  We really want this to be "get n bits".
  143          */
  144         rec_q = rs->rec_q;
  145         do {
  146                 c = pullbit(&rs->pp);
  147                 rec_q &= lower_bits_rubin;
  148                 rec_q <<= 1;
  149                 rec_q += c;
  150         } while (--bits);
  151         rs->rec_q = rec_q;
  152 }
  153 
  154 int decode(struct rubin_state *rs, long A, long B)
  155 {
  156         unsigned long p = rs->p, q = rs->q;
  157         long i0, threshold;
  158         int symbol;
  159 
  160         if (q >= UPPER_BIT_RUBIN || ((p + q) <= UPPER_BIT_RUBIN))
  161                 __do_decode(rs, p, q);
  162 
  163         i0 = A * rs->p / (A + B);
  164         if (i0 <= 0) {
  165                 i0 = 1;
  166         }
  167         if (i0 >= rs->p) {
  168                 i0 = rs->p - 1;
  169         }
  170 
  171         threshold = rs->q + i0;
  172         symbol = rs->rec_q >= threshold;
  173         if (rs->rec_q >= threshold) {
  174                 rs->q += i0;
  175                 i0 = rs->p - i0;
  176         }
  177 
  178         rs->p = i0;
  179 
  180         return symbol;
  181 }
  182 
  183 
  184 
  185 static int out_byte(struct rubin_state *rs, unsigned char byte)
  186 {
  187         int i, ret;
  188         struct rubin_state rs_copy;
  189         rs_copy = *rs;
  190 
  191         for (i=0;i<8;i++) {
  192                 ret = encode(rs, rs->bit_divider-rs->bits[i],rs->bits[i],byte&1);
  193                 if (ret) {
  194                         /* Failed. Restore old state */
  195                         *rs = rs_copy;
  196                         return ret;
  197                 }
  198                 byte=byte>>1;
  199         }
  200         return 0;
  201 }
  202 
  203 static int in_byte(struct rubin_state *rs)
  204 {
  205         int i, result = 0, bit_divider = rs->bit_divider;
  206 
  207         for (i = 0; i < 8; i++)
  208                 result |= decode(rs, bit_divider - rs->bits[i], rs->bits[i]) << i;
  209 
  210         return result;
  211 }
  212 
  213 
  214 
  215 int rubin_do_compress(int bit_divider, int *bits, unsigned char *data_in, 
  216                       unsigned char *cpage_out, __u32 *sourcelen, __u32 *dstlen)
  217         {
  218         int outpos = 0;
  219         int pos=0;
  220         struct rubin_state rs;
  221 
  222         init_pushpull(&rs.pp, cpage_out, *dstlen * 8, 0, 32);
  223 
  224         init_rubin(&rs, bit_divider, bits);
  225         
  226         while (pos < (*sourcelen) && !out_byte(&rs, data_in[pos]))
  227                 pos++;
  228         
  229         end_rubin(&rs);
  230 
  231         if (outpos > pos) {
  232                 /* We failed */
  233                 return -1;
  234         }
  235         
  236         /* Tell the caller how much we managed to compress, 
  237          * and how much space it took */
  238         
  239         outpos = (pushedbits(&rs.pp)+7)/8;
  240         
  241         if (outpos >= pos)
  242                 return -1; /* We didn't actually compress */
  243         *sourcelen = pos;
  244         *dstlen = outpos;
  245         return 0;
  246 }                  
  247 #if 0
  248 /* _compress returns the compressed size, -1 if bigger */
  249 int rubinmips_compress(unsigned char *data_in, unsigned char *cpage_out, 
  250                    __u32 *sourcelen, __u32 *dstlen)
  251 {
  252         return rubin_do_compress(BIT_DIVIDER_MIPS, bits_mips, data_in, cpage_out, sourcelen, dstlen);
  253 }
  254 #endif
  255 int dynrubin_compress(unsigned char *data_in, unsigned char *cpage_out, 
  256                    __u32 *sourcelen, __u32 *dstlen)
  257 {
  258         int bits[8];
  259         unsigned char histo[256];
  260         int i;
  261         int ret;
  262         __u32 mysrclen, mydstlen;
  263 
  264         mysrclen = *sourcelen;
  265         mydstlen = *dstlen - 8;
  266 
  267         if (*dstlen <= 12)
  268                 return -1;
  269 
  270         memset(histo, 0, 256);
  271         for (i=0; i<mysrclen; i++) {
  272                 histo[data_in[i]]++;
  273         }
  274         memset(bits, 0, sizeof(int)*8);
  275         for (i=0; i<256; i++) {
  276                 if (i&128)
  277                         bits[7] += histo[i];
  278                 if (i&64)
  279                         bits[6] += histo[i];
  280                 if (i&32)
  281                         bits[5] += histo[i];
  282                 if (i&16)
  283                         bits[4] += histo[i];
  284                 if (i&8)
  285                         bits[3] += histo[i];
  286                 if (i&4)
  287                         bits[2] += histo[i];
  288                 if (i&2)
  289                         bits[1] += histo[i];
  290                 if (i&1)
  291                         bits[0] += histo[i];
  292         }
  293 
  294         for (i=0; i<8; i++) {
  295                 bits[i] = (bits[i] * 256) / mysrclen;
  296                 if (!bits[i]) bits[i] = 1;
  297                 if (bits[i] > 255) bits[i] = 255;
  298                 cpage_out[i] = bits[i];
  299         }
  300 
  301         ret = rubin_do_compress(256, bits, data_in, cpage_out+8, &mysrclen, &mydstlen);
  302         if (ret) 
  303                 return ret;
  304 
  305         /* Add back the 8 bytes we took for the probabilities */
  306         mydstlen += 8;
  307 
  308         if (mysrclen <= mydstlen) {
  309                 /* We compressed */
  310                 return -1;
  311         }
  312 
  313         *sourcelen = mysrclen;
  314         *dstlen = mydstlen;
  315         return 0;
  316 }
  317 
  318 void rubin_do_decompress(int bit_divider, int *bits, unsigned char *cdata_in, 
  319                          unsigned char *page_out, __u32 srclen, __u32 destlen)
  320 {
  321         int outpos = 0;
  322         struct rubin_state rs;
  323         
  324         init_pushpull(&rs.pp, cdata_in, srclen, 0, 0);
  325         init_decode(&rs, bit_divider, bits);
  326         
  327         while (outpos < destlen) {
  328                 page_out[outpos++] = in_byte(&rs);
  329         }
  330 }                  
  331 
  332 
  333 void rubinmips_decompress(unsigned char *data_in, unsigned char *cpage_out, 
  334                    __u32 sourcelen, __u32 dstlen)
  335 {
  336         rubin_do_decompress(BIT_DIVIDER_MIPS, bits_mips, data_in, cpage_out, sourcelen, dstlen);
  337 }
  338 
  339 void dynrubin_decompress(unsigned char *data_in, unsigned char *cpage_out, 
  340                    __u32 sourcelen, __u32 dstlen)
  341 {
  342         int bits[8];
  343         int c;
  344 
  345         for (c=0; c<8; c++)
  346                 bits[c] = data_in[c];
  347 
  348         rubin_do_decompress(256, bits, data_in+8, cpage_out, sourcelen-8, dstlen);
  349 }
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FreeBSD/Linux Kernel Cross Reference sys/fs/jffs2/compr_rubin.c

FreeBSD/Linux Kernel Cross Reference
sys/fs/jffs2/compr_rubin.c
