linux/fs/jffs2/compr_rubin.c
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   1/*
   2 * JFFS2 -- Journalling Flash File System, Version 2.
   3 *
   4 * Copyright © 2001-2007 Red Hat, Inc.
   5 * Copyright © 2004-2010 David Woodhouse <dwmw2@infradead.org>
   6 *
   7 * Created by Arjan van de Ven <arjanv@redhat.com>
   8 *
   9 * For licensing information, see the file 'LICENCE' in this directory.
  10 *
  11 */
  12
  13#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  14
  15#include <linux/string.h>
  16#include <linux/types.h>
  17#include <linux/jffs2.h>
  18#include <linux/errno.h>
  19#include "compr.h"
  20
  21
  22#define RUBIN_REG_SIZE   16
  23#define UPPER_BIT_RUBIN    (((long) 1)<<(RUBIN_REG_SIZE-1))
  24#define LOWER_BITS_RUBIN   ((((long) 1)<<(RUBIN_REG_SIZE-1))-1)
  25
  26
  27#define BIT_DIVIDER_MIPS 1043
  28static int bits_mips[8] = { 277, 249, 290, 267, 229, 341, 212, 241};
  29
  30struct pushpull {
  31        unsigned char *buf;
  32        unsigned int buflen;
  33        unsigned int ofs;
  34        unsigned int reserve;
  35};
  36
  37struct rubin_state {
  38        unsigned long p;
  39        unsigned long q;
  40        unsigned long rec_q;
  41        long bit_number;
  42        struct pushpull pp;
  43        int bit_divider;
  44        int bits[8];
  45};
  46
  47static inline void init_pushpull(struct pushpull *pp, char *buf,
  48                                 unsigned buflen, unsigned ofs,
  49                                 unsigned reserve)
  50{
  51        pp->buf = buf;
  52        pp->buflen = buflen;
  53        pp->ofs = ofs;
  54        pp->reserve = reserve;
  55}
  56
  57static inline int pushbit(struct pushpull *pp, int bit, int use_reserved)
  58{
  59        if (pp->ofs >= pp->buflen - (use_reserved?0:pp->reserve))
  60                return -ENOSPC;
  61
  62        if (bit)
  63                pp->buf[pp->ofs >> 3] |= (1<<(7-(pp->ofs & 7)));
  64        else
  65                pp->buf[pp->ofs >> 3] &= ~(1<<(7-(pp->ofs & 7)));
  66
  67        pp->ofs++;
  68
  69        return 0;
  70}
  71
  72static inline int pushedbits(struct pushpull *pp)
  73{
  74        return pp->ofs;
  75}
  76
  77static inline int pullbit(struct pushpull *pp)
  78{
  79        int bit;
  80
  81        bit = (pp->buf[pp->ofs >> 3] >> (7-(pp->ofs & 7))) & 1;
  82
  83        pp->ofs++;
  84        return bit;
  85}
  86
  87static inline int pulledbits(struct pushpull *pp)
  88{
  89        return pp->ofs;
  90}
  91
  92
  93static void init_rubin(struct rubin_state *rs, int div, int *bits)
  94{
  95        int c;
  96
  97        rs->q = 0;
  98        rs->p = (long) (2 * UPPER_BIT_RUBIN);
  99        rs->bit_number = (long) 0;
 100        rs->bit_divider = div;
 101
 102        for (c=0; c<8; c++)
 103                rs->bits[c] = bits[c];
 104}
 105
 106
 107static int encode(struct rubin_state *rs, long A, long B, int symbol)
 108{
 109
 110        long i0, i1;
 111        int ret;
 112
 113        while ((rs->q >= UPPER_BIT_RUBIN) ||
 114               ((rs->p + rs->q) <= UPPER_BIT_RUBIN)) {
 115                rs->bit_number++;
 116
 117                ret = pushbit(&rs->pp, (rs->q & UPPER_BIT_RUBIN) ? 1 : 0, 0);
 118                if (ret)
 119                        return ret;
 120                rs->q &= LOWER_BITS_RUBIN;
 121                rs->q <<= 1;
 122                rs->p <<= 1;
 123        }
 124        i0 = A * rs->p / (A + B);
 125        if (i0 <= 0)
 126                i0 = 1;
 127
 128        if (i0 >= rs->p)
 129                i0 = rs->p - 1;
 130
 131        i1 = rs->p - i0;
 132
 133        if (symbol == 0)
 134                rs->p = i0;
 135        else {
 136                rs->p = i1;
 137                rs->q += i0;
 138        }
 139        return 0;
 140}
 141
 142
 143static void end_rubin(struct rubin_state *rs)
 144{
 145
 146        int i;
 147
 148        for (i = 0; i < RUBIN_REG_SIZE; i++) {
 149                pushbit(&rs->pp, (UPPER_BIT_RUBIN & rs->q) ? 1 : 0, 1);
 150                rs->q &= LOWER_BITS_RUBIN;
 151                rs->q <<= 1;
 152        }
 153}
 154
 155
 156static void init_decode(struct rubin_state *rs, int div, int *bits)
 157{
 158        init_rubin(rs, div, bits);
 159
 160        /* behalve lower */
 161        rs->rec_q = 0;
 162
 163        for (rs->bit_number = 0; rs->bit_number++ < RUBIN_REG_SIZE;
 164             rs->rec_q = rs->rec_q * 2 + (long) (pullbit(&rs->pp)))
 165                ;
 166}
 167
 168static void __do_decode(struct rubin_state *rs, unsigned long p,
 169                        unsigned long q)
 170{
 171        register unsigned long lower_bits_rubin = LOWER_BITS_RUBIN;
 172        unsigned long rec_q;
 173        int c, bits = 0;
 174
 175        /*
 176         * First, work out how many bits we need from the input stream.
 177         * Note that we have already done the initial check on this
 178         * loop prior to calling this function.
 179         */
 180        do {
 181                bits++;
 182                q &= lower_bits_rubin;
 183                q <<= 1;
 184                p <<= 1;
 185        } while ((q >= UPPER_BIT_RUBIN) || ((p + q) <= UPPER_BIT_RUBIN));
 186
 187        rs->p = p;
 188        rs->q = q;
 189
 190        rs->bit_number += bits;
 191
 192        /*
 193         * Now get the bits.  We really want this to be "get n bits".
 194         */
 195        rec_q = rs->rec_q;
 196        do {
 197                c = pullbit(&rs->pp);
 198                rec_q &= lower_bits_rubin;
 199                rec_q <<= 1;
 200                rec_q += c;
 201        } while (--bits);
 202        rs->rec_q = rec_q;
 203}
 204
 205static int decode(struct rubin_state *rs, long A, long B)
 206{
 207        unsigned long p = rs->p, q = rs->q;
 208        long i0, threshold;
 209        int symbol;
 210
 211        if (q >= UPPER_BIT_RUBIN || ((p + q) <= UPPER_BIT_RUBIN))
 212                __do_decode(rs, p, q);
 213
 214        i0 = A * rs->p / (A + B);
 215        if (i0 <= 0)
 216                i0 = 1;
 217
 218        if (i0 >= rs->p)
 219                i0 = rs->p - 1;
 220
 221        threshold = rs->q + i0;
 222        symbol = rs->rec_q >= threshold;
 223        if (rs->rec_q >= threshold) {
 224                rs->q += i0;
 225                i0 = rs->p - i0;
 226        }
 227
 228        rs->p = i0;
 229
 230        return symbol;
 231}
 232
 233
 234
 235static int out_byte(struct rubin_state *rs, unsigned char byte)
 236{
 237        int i, ret;
 238        struct rubin_state rs_copy;
 239        rs_copy = *rs;
 240
 241        for (i=0; i<8; i++) {
 242                ret = encode(rs, rs->bit_divider-rs->bits[i],
 243                             rs->bits[i], byte & 1);
 244                if (ret) {
 245                        /* Failed. Restore old state */
 246                        *rs = rs_copy;
 247                        return ret;
 248                }
 249                byte >>= 1 ;
 250        }
 251        return 0;
 252}
 253
 254static int in_byte(struct rubin_state *rs)
 255{
 256        int i, result = 0, bit_divider = rs->bit_divider;
 257
 258        for (i = 0; i < 8; i++)
 259                result |= decode(rs, bit_divider - rs->bits[i],
 260                                 rs->bits[i]) << i;
 261
 262        return result;
 263}
 264
 265
 266
 267static int rubin_do_compress(int bit_divider, int *bits, unsigned char *data_in,
 268                             unsigned char *cpage_out, uint32_t *sourcelen,
 269                             uint32_t *dstlen)
 270        {
 271        int outpos = 0;
 272        int pos=0;
 273        struct rubin_state rs;
 274
 275        init_pushpull(&rs.pp, cpage_out, *dstlen * 8, 0, 32);
 276
 277        init_rubin(&rs, bit_divider, bits);
 278
 279        while (pos < (*sourcelen) && !out_byte(&rs, data_in[pos]))
 280                pos++;
 281
 282        end_rubin(&rs);
 283
 284        if (outpos > pos) {
 285                /* We failed */
 286                return -1;
 287        }
 288
 289        /* Tell the caller how much we managed to compress,
 290         * and how much space it took */
 291
 292        outpos = (pushedbits(&rs.pp)+7)/8;
 293
 294        if (outpos >= pos)
 295                return -1; /* We didn't actually compress */
 296        *sourcelen = pos;
 297        *dstlen = outpos;
 298        return 0;
 299}
 300#if 0
 301/* _compress returns the compressed size, -1 if bigger */
 302int jffs2_rubinmips_compress(unsigned char *data_in, unsigned char *cpage_out,
 303                   uint32_t *sourcelen, uint32_t *dstlen)
 304{
 305        return rubin_do_compress(BIT_DIVIDER_MIPS, bits_mips, data_in,
 306                                 cpage_out, sourcelen, dstlen);
 307}
 308#endif
 309static int jffs2_dynrubin_compress(unsigned char *data_in,
 310                                   unsigned char *cpage_out,
 311                                   uint32_t *sourcelen, uint32_t *dstlen)
 312{
 313        int bits[8];
 314        unsigned char histo[256];
 315        int i;
 316        int ret;
 317        uint32_t mysrclen, mydstlen;
 318
 319        mysrclen = *sourcelen;
 320        mydstlen = *dstlen - 8;
 321
 322        if (*dstlen <= 12)
 323                return -1;
 324
 325        memset(histo, 0, 256);
 326        for (i=0; i<mysrclen; i++)
 327                histo[data_in[i]]++;
 328        memset(bits, 0, sizeof(int)*8);
 329        for (i=0; i<256; i++) {
 330                if (i&128)
 331                        bits[7] += histo[i];
 332                if (i&64)
 333                        bits[6] += histo[i];
 334                if (i&32)
 335                        bits[5] += histo[i];
 336                if (i&16)
 337                        bits[4] += histo[i];
 338                if (i&8)
 339                        bits[3] += histo[i];
 340                if (i&4)
 341                        bits[2] += histo[i];
 342                if (i&2)
 343                        bits[1] += histo[i];
 344                if (i&1)
 345                        bits[0] += histo[i];
 346        }
 347
 348        for (i=0; i<8; i++) {
 349                bits[i] = (bits[i] * 256) / mysrclen;
 350                if (!bits[i]) bits[i] = 1;
 351                if (bits[i] > 255) bits[i] = 255;
 352                cpage_out[i] = bits[i];
 353        }
 354
 355        ret = rubin_do_compress(256, bits, data_in, cpage_out+8, &mysrclen,
 356                                &mydstlen);
 357        if (ret)
 358                return ret;
 359
 360        /* Add back the 8 bytes we took for the probabilities */
 361        mydstlen += 8;
 362
 363        if (mysrclen <= mydstlen) {
 364                /* We compressed */
 365                return -1;
 366        }
 367
 368        *sourcelen = mysrclen;
 369        *dstlen = mydstlen;
 370        return 0;
 371}
 372
 373static void rubin_do_decompress(int bit_divider, int *bits,
 374                                unsigned char *cdata_in, 
 375                                unsigned char *page_out, uint32_t srclen,
 376                                uint32_t destlen)
 377{
 378        int outpos = 0;
 379        struct rubin_state rs;
 380
 381        init_pushpull(&rs.pp, cdata_in, srclen, 0, 0);
 382        init_decode(&rs, bit_divider, bits);
 383
 384        while (outpos < destlen)
 385                page_out[outpos++] = in_byte(&rs);
 386}
 387
 388
 389static int jffs2_rubinmips_decompress(unsigned char *data_in,
 390                                      unsigned char *cpage_out,
 391                                      uint32_t sourcelen, uint32_t dstlen)
 392{
 393        rubin_do_decompress(BIT_DIVIDER_MIPS, bits_mips, data_in,
 394                            cpage_out, sourcelen, dstlen);
 395        return 0;
 396}
 397
 398static int jffs2_dynrubin_decompress(unsigned char *data_in,
 399                                     unsigned char *cpage_out,
 400                                     uint32_t sourcelen, uint32_t dstlen)
 401{
 402        int bits[8];
 403        int c;
 404
 405        for (c=0; c<8; c++)
 406                bits[c] = data_in[c];
 407
 408        rubin_do_decompress(256, bits, data_in+8, cpage_out, sourcelen-8,
 409                            dstlen);
 410        return 0;
 411}
 412
 413static struct jffs2_compressor jffs2_rubinmips_comp = {
 414        .priority = JFFS2_RUBINMIPS_PRIORITY,
 415        .name = "rubinmips",
 416        .compr = JFFS2_COMPR_DYNRUBIN,
 417        .compress = NULL, /*&jffs2_rubinmips_compress,*/
 418        .decompress = &jffs2_rubinmips_decompress,
 419#ifdef JFFS2_RUBINMIPS_DISABLED
 420        .disabled = 1,
 421#else
 422        .disabled = 0,
 423#endif
 424};
 425
 426int jffs2_rubinmips_init(void)
 427{
 428        return jffs2_register_compressor(&jffs2_rubinmips_comp);
 429}
 430
 431void jffs2_rubinmips_exit(void)
 432{
 433        jffs2_unregister_compressor(&jffs2_rubinmips_comp);
 434}
 435
 436static struct jffs2_compressor jffs2_dynrubin_comp = {
 437        .priority = JFFS2_DYNRUBIN_PRIORITY,
 438        .name = "dynrubin",
 439        .compr = JFFS2_COMPR_RUBINMIPS,
 440        .compress = jffs2_dynrubin_compress,
 441        .decompress = &jffs2_dynrubin_decompress,
 442#ifdef JFFS2_DYNRUBIN_DISABLED
 443        .disabled = 1,
 444#else
 445        .disabled = 0,
 446#endif
 447};
 448
 449int jffs2_dynrubin_init(void)
 450{
 451        return jffs2_register_compressor(&jffs2_dynrubin_comp);
 452}
 453
 454void jffs2_dynrubin_exit(void)
 455{
 456        jffs2_unregister_compressor(&jffs2_dynrubin_comp);
 457}
 458
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