decompress_uncompress.c

arm9200t上的一个叫busybox的东西

#include "config.h"
#include "libbb.h"

/* uncompress for busybox -- (c) 2002 Robert Griebl
 *
 * based on the original compress42.c source
 * (see disclaimer below)
 */


/* (N)compress42.c - File compression ala IEEE Computer, Mar 1992.
 *
 * Authors:
 *   Spencer W. Thomas   (decvax!harpo!utah-cs!utah-gr!thomas)
 *   Jim McKie           (decvax!mcvax!jim)
 *   Steve Davies        (decvax!vax135!petsd!peora!srd)
 *   Ken Turkowski       (decvax!decwrl!turtlevax!ken)
 *   James A. Woods      (decvax!ihnp4!ames!jaw)
 *   Joe Orost           (decvax!vax135!petsd!joe)
 *   Dave Mack           ([e-mail])
 *   Peter Jannesen, Network Communication Systems
 *                       ([e-mail])
 *
 * [e-mail] : a small security fix for a buffer overflow
 *
 * [... History snipped ...]
 *
 */
#include <stdio.h>
#include <string.h>
#include <unistd.h>

/* Default input buffer size */
#define	IBUFSIZ	2048

/* Default output buffer size */
#define	OBUFSIZ	2048

/* Defines for third byte of header */
#define	MAGIC_1		(char_type)'\037'	/* First byte of compressed file               */
#define	MAGIC_2		(char_type)'\235'	/* Second byte of compressed file              */
#define BIT_MASK	0x1f	/* Mask for 'number of compresssion bits'       */
							/* Masks 0x20 and 0x40 are free.                */
							/* I think 0x20 should mean that there is       */
							/* a fourth header byte (for expansion).        */
#define BLOCK_MODE	0x80	/* Block compresssion if table is full and      */
			/* compression rate is dropping flush tables    */
			/* the next two codes should not be changed lightly, as they must not   */
			/* lie within the contiguous general code space.                        */
#define FIRST	257		/* first free entry                             */
#define	CLEAR	256		/* table clear output code                      */

#define INIT_BITS 9		/* initial number of bits/code */


/* machine variants which require cc -Dmachine:  pdp11, z8000, DOS */
#define FAST

#define	HBITS		17	/* 50% occupancy */
#define	HSIZE	   (1<<HBITS)
#define	HMASK	   (HSIZE-1)
#define	HPRIME		 9941
#define	BITS		   16
#undef	MAXSEG_64K
#define MAXCODE(n)	(1L << (n))

/* Block compress mode -C compatible with 2.0 */
int block_mode = BLOCK_MODE;

/* user settable max # bits/code */
int maxbits = BITS;

/* Exitcode of compress (-1 no file compressed) */
int exit_code = -1;

/* Input buffer */
unsigned char inbuf[IBUFSIZ + 64];

/* Output buffer */
unsigned char outbuf[OBUFSIZ + 2048];


long int htab[HSIZE];
unsigned short codetab[HSIZE];

#define	htabof(i)				htab[i]
#define	codetabof(i)			codetab[i]
#define	tab_prefixof(i)			codetabof(i)
#define	tab_suffixof(i)			((unsigned char *)(htab))[i]
#define	de_stack				((unsigned char *)&(htab[HSIZE-1]))
#define	clear_htab()			memset(htab, -1, sizeof(htab))
#define	clear_tab_prefixof()	memset(codetab, 0, 256);


/*
 * Decompress stdin to stdout.  This routine adapts to the codes in the
 * file building the "string" table on-the-fly; requiring no table to
 * be stored in the compressed file.  The tables used herein are shared
 * with those of the compress() routine.  See the definitions above.
 */

extern int uncompress(int fd_in, int fd_out)
{
	unsigned char *stackp;
	long int code;
	int finchar;
	long int oldcode;
	long int incode;
	int inbits;
	int posbits;
	int outpos;
	int insize;
	int bitmask;
	long int free_ent;
	long int maxcode;
	long int maxmaxcode;
	int n_bits;
	int rsize = 0;

	insize = 0;

	inbuf[0] = bb_xread_char(fd_in);

	maxbits = inbuf[0] & BIT_MASK;
	block_mode = inbuf[0] & BLOCK_MODE;
	maxmaxcode = MAXCODE(maxbits);

	if (maxbits > BITS) {
		bb_error_msg("compressed with %d bits, can only handle %d bits", maxbits,
				  BITS);
		return -1;
	}

	maxcode = MAXCODE(n_bits = INIT_BITS) - 1;
	bitmask = (1 << n_bits) - 1;
	oldcode = -1;
	finchar = 0;
	outpos = 0;
	posbits = 0 << 3;

	free_ent = ((block_mode) ? FIRST : 256);

	/* As above, initialize the first 256 entries in the table. */
	clear_tab_prefixof();

	for (code = 255; code >= 0; --code) {
		tab_suffixof(code) = (unsigned char) code;
	}

	do {
	  resetbuf:;
		{
			int i;
			int e;
			int o;

			e = insize - (o = (posbits >> 3));

			for (i = 0; i < e; ++i)
				inbuf[i] = inbuf[i + o];

			insize = e;
			posbits = 0;
		}

		if (insize < (int) sizeof(inbuf) - IBUFSIZ) {
			rsize = safe_read(fd_in, inbuf + insize, IBUFSIZ);
			insize += rsize;
		}

		inbits = ((rsize > 0) ? (insize - insize % n_bits) << 3 :
				  (insize << 3) - (n_bits - 1));

		while (inbits > posbits) {
			if (free_ent > maxcode) {
				posbits =
					((posbits - 1) +
					 ((n_bits << 3) -
					  (posbits - 1 + (n_bits << 3)) % (n_bits << 3)));
				++n_bits;
				if (n_bits == maxbits) {
					maxcode = maxmaxcode;
				} else {
					maxcode = MAXCODE(n_bits) - 1;
				}
				bitmask = (1 << n_bits) - 1;
				goto resetbuf;
			}
			{
				unsigned char *p = &inbuf[posbits >> 3];

				code =
					((((long) (p[0])) | ((long) (p[1]) << 8) |
					  ((long) (p[2]) << 16)) >> (posbits & 0x7)) & bitmask;
			}
			posbits += n_bits;


			if (oldcode == -1) {
				outbuf[outpos++] = (unsigned char) (finchar =
												(int) (oldcode = code));
				continue;
			}

			if (code == CLEAR && block_mode) {
				clear_tab_prefixof();
				free_ent = FIRST - 1;
				posbits =
					((posbits - 1) +
					 ((n_bits << 3) -
					  (posbits - 1 + (n_bits << 3)) % (n_bits << 3)));
				maxcode = MAXCODE(n_bits = INIT_BITS) - 1;
				bitmask = (1 << n_bits) - 1;
				goto resetbuf;
			}

			incode = code;
			stackp = de_stack;

			/* Special case for KwKwK string. */
			if (code >= free_ent) {
				if (code > free_ent) {
					unsigned char *p;

					posbits -= n_bits;
					p = &inbuf[posbits >> 3];

					bb_error_msg
						("insize:%d posbits:%d inbuf:%02X %02X %02X %02X %02X (%d)",
						 insize, posbits, p[-1], p[0], p[1], p[2], p[3],
						 (posbits & 07));
					bb_error_msg("uncompress: corrupt input");
					return -1;
				}

				*--stackp = (unsigned char) finchar;
				code = oldcode;
			}

			/* Generate output characters in reverse order */
			while ((long int) code >= (long int) 256) {
				*--stackp = tab_suffixof(code);
				code = tab_prefixof(code);
			}

			*--stackp = (unsigned char) (finchar = tab_suffixof(code));

			/* And put them out in forward order */
			{
				int i;

				if (outpos + (i = (de_stack - stackp)) >= OBUFSIZ) {
					do {
						if (i > OBUFSIZ - outpos) {
							i = OBUFSIZ - outpos;
						}

						if (i > 0) {
							memcpy(outbuf + outpos, stackp, i);
							outpos += i;
						}

						if (outpos >= OBUFSIZ) {
							write(fd_out, outbuf, outpos);
							outpos = 0;
						}
						stackp += i;
					} while ((i = (de_stack - stackp)) > 0);
				} else {
					memcpy(outbuf + outpos, stackp, i);
					outpos += i;
				}
			}

			/* Generate the new entry. */
			if ((code = free_ent) < maxmaxcode) {
				tab_prefixof(code) = (unsigned short) oldcode;
				tab_suffixof(code) = (unsigned char) finchar;
				free_ent = code + 1;
			}

			/* Remember previous code.  */
			oldcode = incode;
		}

	} while (rsize > 0);

	if (outpos > 0) {
		write(fd_out, outbuf, outpos);
	}

	return 0;
}