isdn_bsdcomp.c

linux-2.6.15.6

	struct bsd_dict *dictp;
	unsigned char c;
	int hval,disp,ilen,mxcode;
	unsigned char *rptr = skb_in->data;
	int isize = skb_in->len;

#define OUTPUT(ent)			\
  {					\
    bitno -= n_bits;			\
    accm |= ((ent) << bitno);		\
    do	{				\
        if(skb_out && skb_tailroom(skb_out) > 0) 	\
      		*(skb_put(skb_out,1)) = (unsigned char) (accm>>24); \
	accm <<= 8;			\
	bitno += 8;			\
    } while (bitno <= 24);		\
  }

	/*
	 * If the protocol is not in the range we're interested in,
	 * just return without compressing the packet.  If it is,
	 * the protocol becomes the first byte to compress.
	 */
	printk(KERN_DEBUG "bsd_compress called with %x\n",proto);
	
	ent = proto;
	if (proto < 0x21 || proto > 0xf9 || !(proto & 0x1) )
		return 0;

	db      = (struct bsd_db *) state;
	hshift  = db->hshift;
	max_ent = db->max_ent;
	n_bits  = db->n_bits;
	bitno   = 32;
	accm    = 0;
	mxcode  = MAXCODE (n_bits);
	
	/* This is the PPP header information */
	if(skb_out && skb_tailroom(skb_out) >= 2) {
		char *v = skb_put(skb_out,2);
		/* we only push our own data on the header,
		  AC,PC and protos is pushed by caller  */
		v[0] = db->seqno >> 8;
		v[1] = db->seqno;
	}

	ilen   = ++isize; /* This is off by one, but that is what is in draft! */

	while (--ilen > 0) {
		c     = *rptr++;
		fcode = BSD_KEY  (ent, c);
		hval  = BSD_HASH (ent, c, hshift);
		dictp = dict_ptr (db, hval);
	
		/* Validate and then check the entry. */
		if (dictp->codem1 >= max_ent)
			goto nomatch;

		if (dictp->fcode == fcode) {
			ent = dictp->codem1 + 1;
			continue;	/* found (prefix,suffix) */
		}
	
		/* continue probing until a match or invalid entry */
		disp = (hval == 0) ? 1 : hval;

		do {
			hval += disp;
			if (hval >= db->hsize)
				hval -= db->hsize;
			dictp = dict_ptr (db, hval);
			if (dictp->codem1 >= max_ent)
				goto nomatch;
		} while (dictp->fcode != fcode);

		ent = dictp->codem1 + 1;	/* finally found (prefix,suffix) */
		continue;
	
nomatch:
		OUTPUT(ent);		/* output the prefix */
	
		/* code -> hashtable */
		if (max_ent < db->maxmaxcode) {
			struct bsd_dict *dictp2;
			struct bsd_dict *dictp3;
			int indx;

			/* expand code size if needed */
			if (max_ent >= mxcode) {
				db->n_bits = ++n_bits;
				mxcode = MAXCODE (n_bits);
			}
	    
			/* 
			 * Invalidate old hash table entry using
			 * this code, and then take it over.
			 */
			dictp2 = dict_ptr (db, max_ent + 1);
			indx   = dictp2->cptr;
			dictp3 = dict_ptr (db, indx);

			if (dictp3->codem1 == max_ent)
				dictp3->codem1 = BADCODEM1;

			dictp2->cptr   = hval;
			dictp->codem1  = max_ent;
			dictp->fcode = fcode;
			db->max_ent    = ++max_ent;

			if (db->lens) {
				unsigned short *len1 = lens_ptr (db, max_ent);
				unsigned short *len2 = lens_ptr (db, ent);
				*len1 = *len2 + 1;
			}
		}
		ent = c;
	}
    
	OUTPUT(ent);		/* output the last code */

	if(skb_out)
		db->bytes_out    += skb_out->len; /* Do not count bytes from here */
	db->uncomp_bytes += isize;
	db->in_count     += isize;
	++db->uncomp_count;
	++db->seqno;

	if (bitno < 32)
		++db->bytes_out; /* must be set before calling bsd_check */

	/*
	 * Generate the clear command if needed
	 */

	if (bsd_check(db))
		OUTPUT (CLEAR);

	/*
	 * Pad dribble bits of last code with ones.
	 * Do not emit a completely useless byte of ones.
	 */
	if (bitno < 32 && skb_out && skb_tailroom(skb_out) > 0) 
		*(skb_put(skb_out,1)) = (unsigned char) ((accm | (0xff << (bitno-8))) >> 24);
    
	/*
	 * Increase code size if we would have without the packet
	 * boundary because the decompressor will do so.
	 */
	if (max_ent >= mxcode && max_ent < db->maxmaxcode)
		db->n_bits++;

	/* If output length is too large then this is an incompressible frame. */
	if (!skb_out || (skb_out && skb_out->len >= skb_in->len) ) {
		++db->incomp_count;
		db->incomp_bytes += isize;
		return 0;
	}

	/* Count the number of compressed frames */
	++db->comp_count;
	db->comp_bytes += skb_out->len;
	return skb_out->len;

#undef OUTPUT
}

/*
 * Update the "BSD Compress" dictionary on the receiver for
 * incompressible data by pretending to compress the incoming data.
 */
static void bsd_incomp (void *state, struct sk_buff *skb_in,int proto)
{
	bsd_compress (state, skb_in, NULL, proto);
}

/*
 * Decompress "BSD Compress".
 */
static int bsd_decompress (void *state, struct sk_buff *skb_in, struct sk_buff *skb_out,
			   struct isdn_ppp_resetparams *rsparm)
{
	struct bsd_db *db;
	unsigned int max_ent;
	unsigned long accm;
	unsigned int bitno;		/* 1st valid bit in accm */
	unsigned int n_bits;
	unsigned int tgtbitno;	/* bitno when we have a code */
	struct bsd_dict *dictp;
	int seq;
	unsigned int incode;
	unsigned int oldcode;
	unsigned int finchar;
	unsigned char *p,*ibuf;
	int ilen;
	int codelen;
	int extra;

	db       = (struct bsd_db *) state;
	max_ent  = db->max_ent;
	accm     = 0;
	bitno    = 32;		/* 1st valid bit in accm */
	n_bits   = db->n_bits;
	tgtbitno = 32 - n_bits;	/* bitno when we have a code */

	printk(KERN_DEBUG "bsd_decompress called\n");

	if(!skb_in || !skb_out) {
		printk(KERN_ERR "bsd_decompress called with NULL parameter\n");
		return DECOMP_ERROR;
	}
    
	/*
	 * Get the sequence number.
	 */
	if( (p = skb_pull(skb_in,2)) == NULL) {
		return DECOMP_ERROR;
	}
	p-=2;
	seq   = (p[0] << 8) + p[1];
	ilen  = skb_in->len;
	ibuf = skb_in->data;

	/*
	 * Check the sequence number and give up if it differs from
	 * the value we're expecting.
	 */
	if (seq != db->seqno) {
		if (db->debug) {
			printk(KERN_DEBUG "bsd_decomp%d: bad sequence # %d, expected %d\n",
				db->unit, seq, db->seqno - 1);
		}
		return DECOMP_ERROR;
	}

	++db->seqno;
	db->bytes_out += ilen;

	if(skb_tailroom(skb_out) > 0)
		*(skb_put(skb_out,1)) = 0;
	else
		return DECOMP_ERR_NOMEM;
    
	oldcode = CLEAR;

	/*
	 * Keep the checkpoint correctly so that incompressible packets
	 * clear the dictionary at the proper times.
	 */

	for (;;) {
		if (ilen-- <= 0) {
			db->in_count += (skb_out->len - 1); /* don't count the header */
			break;
		}

		/*
		 * Accumulate bytes until we have a complete code.
		 * Then get the next code, relying on the 32-bit,
		 * unsigned accm to mask the result.
		 */

		bitno -= 8;
		accm  |= *ibuf++ << bitno;
		if (tgtbitno < bitno)
			continue;

		incode = accm >> tgtbitno;
		accm <<= n_bits;
		bitno += n_bits;

		/*
		 * The dictionary must only be cleared at the end of a packet.
		 */
	
		if (incode == CLEAR) {
			if (ilen > 0) {
				if (db->debug)
					printk(KERN_DEBUG "bsd_decomp%d: bad CLEAR\n", db->unit);
				return DECOMP_FATALERROR;	/* probably a bug */
			}
			bsd_clear(db);
			break;
		}

		if ((incode > max_ent + 2) || (incode > db->maxmaxcode)
			|| (incode > max_ent && oldcode == CLEAR)) {
			if (db->debug) {
				printk(KERN_DEBUG "bsd_decomp%d: bad code 0x%x oldcode=0x%x ",
					db->unit, incode, oldcode);
				printk(KERN_DEBUG "max_ent=0x%x skb->Len=%d seqno=%d\n",
					max_ent, skb_out->len, db->seqno);
			}
			return DECOMP_FATALERROR;	/* probably a bug */
		}
	
		/* Special case for KwKwK string. */
		if (incode > max_ent) {
			finchar = oldcode;
			extra   = 1;
		} else {
			finchar = incode;
			extra   = 0;
		}

		codelen = *(lens_ptr (db, finchar));
		if( skb_tailroom(skb_out) < codelen + extra) {
			if (db->debug) {
				printk(KERN_DEBUG "bsd_decomp%d: ran out of mru\n", db->unit);
#ifdef DEBUG
				printk(KERN_DEBUG "  len=%d, finchar=0x%x, codelen=%d,skblen=%d\n",
					ilen, finchar, codelen, skb_out->len);
#endif
			}
			return DECOMP_FATALERROR;
		}

		/*
		 * Decode this code and install it in the decompressed buffer.
		 */

		p     = skb_put(skb_out,codelen);
		p += codelen;
		while (finchar > LAST) {
			struct bsd_dict *dictp2 = dict_ptr (db, finchar);
	    
			dictp = dict_ptr (db, dictp2->cptr);

#ifdef DEBUG
			if (--codelen <= 0 || dictp->codem1 != finchar-1) {
				if (codelen <= 0) {
					printk(KERN_ERR "bsd_decomp%d: fell off end of chain ", db->unit);
					printk(KERN_ERR "0x%x at 0x%x by 0x%x, max_ent=0x%x\n", incode, finchar, dictp2->cptr, max_ent);
				} else {
					if (dictp->codem1 != finchar-1) {
						printk(KERN_ERR "bsd_decomp%d: bad code chain 0x%x finchar=0x%x ",db->unit, incode, finchar);
						printk(KERN_ERR "oldcode=0x%x cptr=0x%x codem1=0x%x\n", oldcode, dictp2->cptr, dictp->codem1);
					}
				}
				return DECOMP_FATALERROR;
			}
#endif

			{
				u32 fcode = dictp->fcode;
				*--p    = (fcode >> 16) & 0xff;
				finchar = fcode & 0xffff;
			}
		}
		*--p = finchar;
	
#ifdef DEBUG
		if (--codelen != 0)
			printk(KERN_ERR "bsd_decomp%d: short by %d after code 0x%x, max_ent=0x%x\n", db->unit, codelen, incode, max_ent);
#endif
	
		if (extra)		/* the KwKwK case again */
			*(skb_put(skb_out,1)) = finchar;
	
		/*
		 * If not first code in a packet, and
		 * if not out of code space, then allocate a new code.
		 *
		 * Keep the hash table correct so it can be used
		 * with uncompressed packets.
		 */
		if (oldcode != CLEAR && max_ent < db->maxmaxcode) {
			struct bsd_dict *dictp2, *dictp3;
			u16  *lens1,  *lens2;
			unsigned long fcode;
			int hval, disp, indx;
	    
			fcode = BSD_KEY(oldcode,finchar);
			hval  = BSD_HASH(oldcode,finchar,db->hshift);
			dictp = dict_ptr (db, hval);
	    
			/* look for a free hash table entry */
			if (dictp->codem1 < max_ent) {
				disp = (hval == 0) ? 1 : hval;
				do {
					hval += disp;
					if (hval >= db->hsize)
						hval -= db->hsize;
					dictp = dict_ptr (db, hval);
				} while (dictp->codem1 < max_ent);
			}
	    
			/*
			 * Invalidate previous hash table entry
			 * assigned this code, and then take it over
			 */

			dictp2 = dict_ptr (db, max_ent + 1);
			indx   = dictp2->cptr;
			dictp3 = dict_ptr (db, indx);

			if (dictp3->codem1 == max_ent)
				dictp3->codem1 = BADCODEM1;

			dictp2->cptr   = hval;
			dictp->codem1  = max_ent;
			dictp->fcode = fcode;
			db->max_ent    = ++max_ent;

			/* Update the length of this string. */
			lens1  = lens_ptr (db, max_ent);
			lens2  = lens_ptr (db, oldcode);
			*lens1 = *lens2 + 1;
	    
			/* Expand code size if needed. */
			if (max_ent >= MAXCODE(n_bits) && max_ent < db->maxmaxcode) {
				db->n_bits = ++n_bits;
				tgtbitno   = 32-n_bits;
			}
		}
		oldcode = incode;
	}

	++db->comp_count;
	++db->uncomp_count;
	db->comp_bytes   += skb_in->len - BSD_OVHD;
	db->uncomp_bytes += skb_out->len;

	if (bsd_check(db)) {
		if (db->debug)
			printk(KERN_DEBUG "bsd_decomp%d: peer should have cleared dictionary on %d\n",
				db->unit, db->seqno - 1);
	}
	return skb_out->len;
}

/*************************************************************
 * Table of addresses for the BSD compression module
 *************************************************************/

static struct isdn_ppp_compressor ippp_bsd_compress = {
	.owner          = THIS_MODULE,
	.num            = CI_BSD_COMPRESS,
	.alloc          = bsd_alloc,
	.free           = bsd_free,
	.init           = bsd_init,
	.reset          = bsd_reset,
	.compress       = bsd_compress,
	.decompress     = bsd_decompress,
	.incomp         = bsd_incomp,
	.stat           = bsd_stats,
};

/*************************************************************
 * Module support routines
 *************************************************************/

static int __init isdn_bsdcomp_init(void)
{
	int answer = isdn_ppp_register_compressor (&ippp_bsd_compress);
	if (answer == 0)
		printk (KERN_INFO "PPP BSD Compression module registered\n");
	return answer;
}

static void __exit isdn_bsdcomp_exit(void)
{
	isdn_ppp_unregister_compressor (&ippp_bsd_compress);
}

module_init(isdn_bsdcomp_init);
module_exit(isdn_bsdcomp_exit);