compr_rubin.c

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/*
 * JFFS2 -- Journalling Flash File System, Version 2.
 *
 * Copyright © 2001-2007 Red Hat, Inc.
 * Copyright © 2004-2010 David Woodhouse <[email protected]>
 *
 * Created by Arjan van de Ven <[email protected]>
 *
 * For licensing information, see the file 'LICENCE' in this directory.
 *
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/string.h>
#include <linux/types.h>
#include <linux/jffs2.h>
#include <linux/errno.h>
#include "compr.h"


#define RUBIN_REG_SIZE   16
#define UPPER_BIT_RUBIN    (((long) 1)<<(RUBIN_REG_SIZE-1))
#define LOWER_BITS_RUBIN   ((((long) 1)<<(RUBIN_REG_SIZE-1))-1)


#define BIT_DIVIDER_MIPS 1043
static int bits_mips[8] = { 277, 249, 290, 267, 229, 341, 212, 241};

struct pushpull {
    unsigned char *buf;
    unsigned int buflen;
    unsigned int ofs;
    unsigned int reserve;
};

struct rubin_state {
    unsigned long p;
    unsigned long q;
    unsigned long rec_q;
    long bit_number;
    struct pushpull pp;
    int bit_divider;
    int bits[8];
};

static inline void init_pushpull(struct pushpull *pp, char *buf,
                 unsigned buflen, unsigned ofs,
                 unsigned reserve)
{
    pp->buf = buf;
    pp->buflen = buflen;
    pp->ofs = ofs;
    pp->reserve = reserve;
}

static inline int pushbit(struct pushpull *pp, int bit, int use_reserved)
{
    if (pp->ofs >= pp->buflen - (use_reserved?0:pp->reserve))
        return -ENOSPC;

    if (bit)
        pp->buf[pp->ofs >> 3] |= (1<<(7-(pp->ofs & 7)));
    else
        pp->buf[pp->ofs >> 3] &= ~(1<<(7-(pp->ofs & 7)));

    pp->ofs++;

    return 0;
}

static inline int pushedbits(struct pushpull *pp)
{
    return pp->ofs;
}

static inline int pullbit(struct pushpull *pp)
{
    int bit;

    bit = (pp->buf[pp->ofs >> 3] >> (7-(pp->ofs & 7))) & 1;

    pp->ofs++;
    return bit;
}

static inline int pulledbits(struct pushpull *pp)
{
    return pp->ofs;
}


static void init_rubin(struct rubin_state *rs, int div, int *bits)
{
    int c;

    rs->q = 0;
    rs->p = (long) (2 * UPPER_BIT_RUBIN);
    rs->bit_number = (long) 0;
    rs->bit_divider = div;

    for (c=0; c<8; c++)
        rs->bits[c] = bits[c];
}


static int encode(struct rubin_state *rs, long A, long B, int symbol)
{

    long i0, i1;
    int ret;

    while ((rs->q >= UPPER_BIT_RUBIN) ||
           ((rs->p + rs->q) <= UPPER_BIT_RUBIN)) {
        rs->bit_number++;

        ret = pushbit(&rs->pp, (rs->q & UPPER_BIT_RUBIN) ? 1 : 0, 0);
        if (ret)
            return ret;
        rs->q &= LOWER_BITS_RUBIN;
        rs->q <<= 1;
        rs->p <<= 1;
    }
    i0 = A * rs->p / (A + B);
    if (i0 <= 0)
        i0 = 1;

    if (i0 >= rs->p)
        i0 = rs->p - 1;

    i1 = rs->p - i0;

    if (symbol == 0)
        rs->p = i0;
    else {
        rs->p = i1;
        rs->q += i0;
    }
    return 0;
}


static void end_rubin(struct rubin_state *rs)
{

    int i;

    for (i = 0; i < RUBIN_REG_SIZE; i++) {
        pushbit(&rs->pp, (UPPER_BIT_RUBIN & rs->q) ? 1 : 0, 1);
        rs->q &= LOWER_BITS_RUBIN;
        rs->q <<= 1;
    }
}


static void init_decode(struct rubin_state *rs, int div, int *bits)
{
    init_rubin(rs, div, bits);

    /* behalve lower */
    rs->rec_q = 0;

    for (rs->bit_number = 0; rs->bit_number++ < RUBIN_REG_SIZE;
         rs->rec_q = rs->rec_q * 2 + (long) (pullbit(&rs->pp)))
        ;
}

static void __do_decode(struct rubin_state *rs, unsigned long p,
            unsigned long q)
{
    register unsigned long lower_bits_rubin = LOWER_BITS_RUBIN;
    unsigned long rec_q;
    int c, bits = 0;

    /*
     * First, work out how many bits we need from the input stream.
     * Note that we have already done the initial check on this
     * loop prior to calling this function.
     */
    do {
        bits++;
        q &= lower_bits_rubin;
        q <<= 1;
        p <<= 1;
    } while ((q >= UPPER_BIT_RUBIN) || ((p + q) <= UPPER_BIT_RUBIN));

    rs->p = p;
    rs->q = q;

    rs->bit_number += bits;

    /*
     * Now get the bits.  We really want this to be "get n bits".
     */
    rec_q = rs->rec_q;
    do {
        c = pullbit(&rs->pp);
        rec_q &= lower_bits_rubin;
        rec_q <<= 1;
        rec_q += c;
    } while (--bits);
    rs->rec_q = rec_q;
}

static int decode(struct rubin_state *rs, long A, long B)
{
    unsigned long p = rs->p, q = rs->q;
    long i0, threshold;
    int symbol;

    if (q >= UPPER_BIT_RUBIN || ((p + q) <= UPPER_BIT_RUBIN))
        __do_decode(rs, p, q);

    i0 = A * rs->p / (A + B);
    if (i0 <= 0)
        i0 = 1;

    if (i0 >= rs->p)
        i0 = rs->p - 1;

    threshold = rs->q + i0;
    symbol = rs->rec_q >= threshold;
    if (rs->rec_q >= threshold) {
        rs->q += i0;
        i0 = rs->p - i0;
    }

    rs->p = i0;

    return symbol;
}



static int out_byte(struct rubin_state *rs, unsigned char byte)
{
    int i, ret;
    struct rubin_state rs_copy;
    rs_copy = *rs;

    for (i=0; i<8; i++) {
        ret = encode(rs, rs->bit_divider-rs->bits[i],
                 rs->bits[i], byte & 1);
        if (ret) {
            /* Failed. Restore old state */
            *rs = rs_copy;
            return ret;
        }
        byte >>= 1 ;
    }
    return 0;
}

static int in_byte(struct rubin_state *rs)
{
    int i, result = 0, bit_divider = rs->bit_divider;

    for (i = 0; i < 8; i++)
        result |= decode(rs, bit_divider - rs->bits[i],
                 rs->bits[i]) << i;

    return result;
}



static int rubin_do_compress(int bit_divider, int *bits, unsigned char *data_in,
                 unsigned char *cpage_out, uint32_t *sourcelen,
                 uint32_t *dstlen)
    {
    int outpos = 0;
    int pos=0;
    struct rubin_state rs;

    init_pushpull(&rs.pp, cpage_out, *dstlen * 8, 0, 32);

    init_rubin(&rs, bit_divider, bits);

    while (pos < (*sourcelen) && !out_byte(&rs, data_in[pos]))
        pos++;

    end_rubin(&rs);

    if (outpos > pos) {
        /* We failed */
        return -1;
    }

    /* Tell the caller how much we managed to compress,
     * and how much space it took */

    outpos = (pushedbits(&rs.pp)+7)/8;

    if (outpos >= pos)
        return -1; /* We didn't actually compress */
    *sourcelen = pos;
    *dstlen = outpos;
    return 0;
}
#if 0
/* _compress returns the compressed size, -1 if bigger */
int jffs2_rubinmips_compress(unsigned char *data_in, unsigned char *cpage_out,
           uint32_t *sourcelen, uint32_t *dstlen)
{
    return rubin_do_compress(BIT_DIVIDER_MIPS, bits_mips, data_in,
                 cpage_out, sourcelen, dstlen);
}
#endif
static int jffs2_dynrubin_compress(unsigned char *data_in,
                   unsigned char *cpage_out,
                   uint32_t *sourcelen, uint32_t *dstlen)
{
    int bits[8];
    unsigned char histo[256];
    int i;
    int ret;
    uint32_t mysrclen, mydstlen;

    mysrclen = *sourcelen;
    mydstlen = *dstlen - 8;

    if (*dstlen <= 12)
        return -1;

    memset(histo, 0, 256);
    for (i=0; i<mysrclen; i++)
        histo[data_in[i]]++;
    memset(bits, 0, sizeof(int)*8);
    for (i=0; i<256; i++) {
        if (i&128)
            bits[7] += histo[i];
        if (i&64)
            bits[6] += histo[i];
        if (i&32)
            bits[5] += histo[i];
        if (i&16)
            bits[4] += histo[i];
        if (i&8)
            bits[3] += histo[i];
        if (i&4)
            bits[2] += histo[i];
        if (i&2)
            bits[1] += histo[i];
        if (i&1)
            bits[0] += histo[i];
    }

    for (i=0; i<8; i++) {
        bits[i] = (bits[i] * 256) / mysrclen;
        if (!bits[i]) bits[i] = 1;
        if (bits[i] > 255) bits[i] = 255;
        cpage_out[i] = bits[i];
    }

    ret = rubin_do_compress(256, bits, data_in, cpage_out+8, &mysrclen,
                &mydstlen);
    if (ret)
        return ret;

    /* Add back the 8 bytes we took for the probabilities */
    mydstlen += 8;

    if (mysrclen <= mydstlen) {
        /* We compressed */
        return -1;
    }

    *sourcelen = mysrclen;
    *dstlen = mydstlen;
    return 0;
}

static void rubin_do_decompress(int bit_divider, int *bits,
                unsigned char *cdata_in, 
                unsigned char *page_out, uint32_t srclen,
                uint32_t destlen)
{
    int outpos = 0;
    struct rubin_state rs;

    init_pushpull(&rs.pp, cdata_in, srclen, 0, 0);
    init_decode(&rs, bit_divider, bits);

    while (outpos < destlen)
        page_out[outpos++] = in_byte(&rs);
}


static int jffs2_rubinmips_decompress(unsigned char *data_in,
                      unsigned char *cpage_out,
                      uint32_t sourcelen, uint32_t dstlen)
{
    rubin_do_decompress(BIT_DIVIDER_MIPS, bits_mips, data_in,
                cpage_out, sourcelen, dstlen);
    return 0;
}

static int jffs2_dynrubin_decompress(unsigned char *data_in,
                     unsigned char *cpage_out,
                     uint32_t sourcelen, uint32_t dstlen)
{
    int bits[8];
    int c;

    for (c=0; c<8; c++)
        bits[c] = data_in[c];

    rubin_do_decompress(256, bits, data_in+8, cpage_out, sourcelen-8,
                dstlen);
    return 0;
}

static struct jffs2_compressor jffs2_rubinmips_comp = {
    .priority = JFFS2_RUBINMIPS_PRIORITY,
    .name = "rubinmips",
    .compr = JFFS2_COMPR_DYNRUBIN,
    .compress = NULL, /*&jffs2_rubinmips_compress,*/
    .decompress = &jffs2_rubinmips_decompress,
#ifdef JFFS2_RUBINMIPS_DISABLED
    .disabled = 1,
#else
    .disabled = 0,
#endif
};

int jffs2_rubinmips_init(void)
{
    return jffs2_register_compressor(&jffs2_rubinmips_comp);
}

void jffs2_rubinmips_exit(void)
{
    jffs2_unregister_compressor(&jffs2_rubinmips_comp);
}

static struct jffs2_compressor jffs2_dynrubin_comp = {
    .priority = JFFS2_DYNRUBIN_PRIORITY,
    .name = "dynrubin",
    .compr = JFFS2_COMPR_RUBINMIPS,
    .compress = jffs2_dynrubin_compress,
    .decompress = &jffs2_dynrubin_decompress,
#ifdef JFFS2_DYNRUBIN_DISABLED
    .disabled = 1,
#else
    .disabled = 0,
#endif
};

int jffs2_dynrubin_init(void)
{
    return jffs2_register_compressor(&jffs2_dynrubin_comp);
}

void jffs2_dynrubin_exit(void)
{
    jffs2_unregister_compressor(&jffs2_dynrubin_comp);
}