source: rtems/cpukit/libfs/src/jffs2/src/compr_rubin.c @ 6ac6a5c8

#include "rtems-jffs2-config.h"

/*
 * JFFS2 -- Journalling Flash File System, Version 2.
 *
 * Copyright © 2001-2007 Red Hat, Inc.
 * Copyright © 2004-2010 David Woodhouse <dwmw2@infradead.org>
 *
 * Created by Arjan van de Ven <arjanv@redhat.com>
 *
 * 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);
}