/*
   * 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);
  }