zopen.c

早期freebsd实现

output(zs, ocode)
	struct s_zstate *zs;
	code_int ocode;
{
	register int bits, r_off;
	register char_type *bp;

	r_off = offset;
	bits = n_bits;
	bp = buf;
	if (ocode >= 0) {
		/* Get to the first byte. */
		bp += (r_off >> 3);
		r_off &= 7;
		/*
		 * Since ocode is always >= 8 bits, only need to mask the first
		 * hunk on the left.
		 */
		*bp = (*bp & rmask[r_off]) | (ocode << r_off) & lmask[r_off];
		bp++;
		bits -= (8 - r_off);
		ocode >>= 8 - r_off;
		/* Get any 8 bit parts in the middle (<=1 for up to 16 bits). */
		if (bits >= 8) {
			*bp++ = ocode;
			ocode >>= 8;
			bits -= 8;
		}
		/* Last bits. */
		if (bits)
			*bp = ocode;
		offset += n_bits;
		if (offset == (n_bits << 3)) {
			bp = buf;
			bits = n_bits;
			bytes_out += bits;
			if (fwrite(bp, sizeof(char), bits, fp) != bits)
				return (-1);
			bp += bits;
			bits = 0;
			offset = 0;
		}
		/*
		 * If the next entry is going to be too big for the ocode size,
		 * then increase it, if possible.
		 */
		if (free_ent > maxcode || (clear_flg > 0)) {
		       /*
			* Write the whole buffer, because the input side won't
			* discover the size increase until after it has read it.
			*/
			if (offset > 0) {
				if (fwrite(buf, 1, n_bits, fp) != n_bits)
					return (-1);
				bytes_out += n_bits;
			}
			offset = 0;

			if (clear_flg) {
				maxcode = MAXCODE(n_bits = INIT_BITS);
				clear_flg = 0;
			} else {
				n_bits++;
				if (n_bits == maxbits)
					maxcode = maxmaxcode;
				else
					maxcode = MAXCODE(n_bits);
			}
		}
	} else {
		/* At EOF, write the rest of the buffer. */
		if (offset > 0) {
			offset = (offset + 7) / 8;
			if (fwrite(buf, 1, offset, fp) != offset)
				return (-1);
			bytes_out += offset;
		}
		offset = 0;
	}
	return (0);
}

/*
 * Decompress read.  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.
 */
static int
zread(cookie, rbp, num)
	void *cookie;
	char *rbp;
	int num;
{
	register u_int count;
	struct s_zstate *zs;
	u_char *bp, header[3];

	if (num == 0)
		return (0);

	zs = cookie;
	count = num;
	bp = (u_char *)rbp;
	switch (state) {
	case S_START:
		state = S_MIDDLE;
		break;
	case S_MIDDLE:
		goto middle;
	case S_EOF:
		goto eof;
	}

	/* Check the magic number */
	if (fread(header,
	    sizeof(char), sizeof(header), fp) != sizeof(header) ||
	    memcmp(header, magic_header, sizeof(magic_header)) != 0) {
		errno = EFTYPE;
		return (-1);
	}
	maxbits = header[2];	/* Set -b from file. */
	block_compress = maxbits & BLOCK_MASK;
	maxbits &= BIT_MASK;
	maxmaxcode = 1L << maxbits;
	if (maxbits > BITS) {
		errno = EFTYPE;
		return (-1);
	}
	/* As above, initialize the first 256 entries in the table. */
	maxcode = MAXCODE(n_bits = INIT_BITS);
	for (code = 255; code >= 0; code--) {
		tab_prefixof(code) = 0;
		tab_suffixof(code) = (char_type) code;
	}
	free_ent = block_compress ? FIRST : 256;

	finchar = oldcode = getcode(zs);
	if (oldcode == -1)	/* EOF already? */
		return (0);	/* Get out of here */

	/* First code must be 8 bits = char. */
	*bp++ = (u_char)finchar;
	count--;
	stackp = de_stack;

	while ((code = getcode(zs)) > -1) {

		if ((code == CLEAR) && block_compress) {
			for (code = 255; code >= 0; code--)
				tab_prefixof(code) = 0;
			clear_flg = 1;
			free_ent = FIRST - 1;
			if ((code = getcode(zs)) == -1)	/* O, untimely death! */
				break;
		}
		incode = code;

		/* Special case for KwKwK string. */
		if (code >= free_ent) {
			*stackp++ = finchar;
			code = oldcode;
		}

		/* Generate output characters in reverse order. */
		while (code >= 256) {
			*stackp++ = tab_suffixof(code);
			code = tab_prefixof(code);
		}
		*stackp++ = finchar = tab_suffixof(code);

		/* And put them out in forward order.  */
middle:		do {
			if (count-- == 0)
				return (num);
			*bp++ = *--stackp;
		} while (stackp > de_stack);

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

		/* Remember previous code. */
		oldcode = incode;
	}
	state = S_EOF;
eof:	return (num - count);
}

/*-
 * Read one code from the standard input.  If EOF, return -1.
 * Inputs:
 * 	stdin
 * Outputs:
 * 	code or -1 is returned.
 */
static code_int
getcode(zs)
	struct s_zstate *zs;
{
	register code_int gcode;
	register int r_off, bits;
	register char_type *bp;

	bp = gbuf;
	if (clear_flg > 0 || roffset >= size || free_ent > maxcode) {
		/*
		 * If the next entry will be too big for the current gcode
		 * size, then we must increase the size.  This implies reading
		 * a new buffer full, too.
		 */
		if (free_ent > maxcode) {
			n_bits++;
			if (n_bits == maxbits)	/* Won't get any bigger now. */
				maxcode = maxmaxcode;
			else
				maxcode = MAXCODE(n_bits);
		}
		if (clear_flg > 0) {
			maxcode = MAXCODE(n_bits = INIT_BITS);
			clear_flg = 0;
		}
		size = fread(gbuf, 1, n_bits, fp);
		if (size <= 0)			/* End of file. */
			return (-1);
		roffset = 0;
		/* Round size down to integral number of codes. */
		size = (size << 3) - (n_bits - 1);
	}
	r_off = roffset;
	bits = n_bits;

	/* Get to the first byte. */
	bp += (r_off >> 3);
	r_off &= 7;

	/* Get first part (low order bits). */
	gcode = (*bp++ >> r_off);
	bits -= (8 - r_off);
	r_off = 8 - r_off;	/* Now, roffset into gcode word. */

	/* Get any 8 bit parts in the middle (<=1 for up to 16 bits). */
	if (bits >= 8) {
		gcode |= *bp++ << r_off;
		r_off += 8;
		bits -= 8;
	}

	/* High order bits. */
	gcode |= (*bp & rmask[bits]) << r_off;
	roffset += n_bits;

	return (gcode);
}

static int
cl_block(zs)			/* Table clear for block compress. */
	struct s_zstate *zs;
{
	register long rat;

	checkpoint = in_count + CHECK_GAP;

	if (in_count > 0x007fffff) {	/* Shift will overflow. */
		rat = bytes_out >> 8;
		if (rat == 0)		/* Don't divide by zero. */
			rat = 0x7fffffff;
		else
			rat = in_count / rat;
	} else
		rat = (in_count << 8) / bytes_out;	/* 8 fractional bits. */
	if (rat > ratio)
		ratio = rat;
	else {
		ratio = 0;
		cl_hash(zs, (count_int) hsize);
		free_ent = FIRST;
		clear_flg = 1;
		if (output(zs, (code_int) CLEAR) == -1)
			return (-1);
	}
	return (0);
}

static void
cl_hash(zs, cl_hsize)			/* Reset code table. */
	struct s_zstate *zs;
	register count_int cl_hsize;
{
	register count_int *htab_p;
	register long i, m1;

	m1 = -1;
	htab_p = htab + cl_hsize;
	i = cl_hsize - 16;
	do {			/* Might use Sys V memset(3) here. */
		*(htab_p - 16) = m1;
		*(htab_p - 15) = m1;
		*(htab_p - 14) = m1;
		*(htab_p - 13) = m1;
		*(htab_p - 12) = m1;
		*(htab_p - 11) = m1;
		*(htab_p - 10) = m1;
		*(htab_p - 9) = m1;
		*(htab_p - 8) = m1;
		*(htab_p - 7) = m1;
		*(htab_p - 6) = m1;
		*(htab_p - 5) = m1;
		*(htab_p - 4) = m1;
		*(htab_p - 3) = m1;
		*(htab_p - 2) = m1;
		*(htab_p - 1) = m1;
		htab_p -= 16;
	} while ((i -= 16) >= 0);
	for (i += 16; i > 0; i--)
		*--htab_p = m1;
}

FILE *
zopen(fname, mode, bits)
	const char *fname, *mode;
	int bits;
{
	struct s_zstate *zs;

	if (mode[0] != 'r' && mode[0] != 'w' || mode[1] != '\0' ||
	    bits < 0 || bits > BITS) {
		errno = EINVAL;
		return (NULL);
	}

	if ((zs = calloc(1, sizeof(struct s_zstate))) == NULL)
		return (NULL);

	maxbits = bits ? bits : BITS;	/* User settable max # bits/code. */
	maxmaxcode = 1 << BITS;		/* Should NEVER generate this code. */
	hsize = HSIZE;			/* For dynamic table sizing. */
	free_ent = 0;			/* First unused entry. */
	block_compress = BLOCK_MASK;
	clear_flg = 0;
	ratio = 0;
	checkpoint = CHECK_GAP;
	in_count = 1;			/* Length of input. */
	out_count = 0;			/* # of codes output (for debugging). */
	state = S_START;
	roffset = 0;
	size = 0;

	/*
	 * Layering compress on top of stdio in order to provide buffering,
	 * and ensure that reads and write work with the data specified.
	 */
	if ((fp = fopen(fname, mode)) == NULL) {
		free(zs);
		return (NULL);
	}
	switch (*mode) {
	case 'r':
		zmode = 'r';
		return (funopen(zs, zread, NULL, NULL, zclose));
	case 'w':
		zmode = 'w';
		return (funopen(zs, NULL, zwrite, NULL, zclose));
	}
	/* NOTREACHED */
}