path: root/gs/src/slzwd.c

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   or she says so in writing.  Refer to the Aladdin Ghostscript Free Public
   License (the "License") for full details.

   Every copy of Aladdin Ghostscript must include a copy of the License,
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   under certain conditions described in the License.  Among other things, the
   License requires that the copyright notice and this notice be preserved on
   all copies.
 */

/* slzwd.c */
/* LZW decoding filter */
#include "stdio_.h"		/* includes std.h */
#include "gdebug.h"
#include "strimpl.h"
#include "slzwx.h"

/* ------ LZWDecode ------ */

/********************************************************/
/* LZW routines are based on:                           */
/* Dr. Dobbs Journal --- Oct. 1989.                     */
/* Article on LZW Data Compression by Mark R. Nelson    */
/********************************************************/

/* Define the special codes in terms of code_escape, which is */
/* 1 << InitialCodeLength. */
#define code_reset (code_escape + 0)
#define code_eod (code_escape + 1)
#define code_0 (code_escape + 2)	/* first assignable code */

struct lzw_decode_s {
    byte datum;
    byte len;			/* length of code */
    ushort prefix;		/* code to be prefixed */
};

gs_private_st_simple(st_lzw_decode, lzw_decode, "lzw_decode");
/* We can use a simple type as the element type, */
/* because there are no pointers to enumerate or relocate. */
#define st_lzw_decode_element st_lzw_decode
#define lzw_decode_max 4096	/* must be 4096 */

#define ss ((stream_LZW_state *)st)

/* Initialize LZWDecode filter */
/* We separate out the reset function for some non-stream clients. */
int
s_LZWD_reset(stream_state * st)
{
    register lzw_decode *dc = ss->table.decode;
    register int i;
    uint code_escape = 1 << ss->InitialCodeLength;

    ss->bits_left = 0;
    ss->bytes_left = 0;
    ss->next_code = code_0;
    ss->code_size = ss->InitialCodeLength + 1;
    ss->prev_code = -1;
    ss->copy_code = -1;
    dc[code_reset].len = 255;
    dc[code_eod].len = 255;
    for (i = 0; i < code_escape; i++, dc++)
	dc->datum = i, dc->len = 1, dc->prefix = code_eod;
    return 0;
}
private int
s_LZWD_init(stream_state * st)
{
    lzw_decode *dc =
    gs_alloc_struct_array(st->memory, lzw_decode_max + 1,
			  lzw_decode, &st_lzw_decode_element,
			  "LZWDecode(init)");

    if (dc == 0)
	return ERRC;
/****** WRONG ******/
    ss->table.decode = dc;
    return s_LZWD_reset(st);
}

/* Process a buffer */
private int
s_LZWD_process(stream_state * st, stream_cursor_read * pr,
	       stream_cursor_write * pw, bool last)
{
    register const byte *p = pr->ptr;
    register byte *q = pw->ptr;

#ifdef DEBUG
    byte *q0 = q;

#endif
    const byte *rlimit = pr->limit;	/* constant pointer */
    byte *wlimit = pw->limit;	/* constant pointer */
    int status = 0;
    int code = ss->copy_code;
    int prev_code = ss->prev_code;
    uint prev_len = ss->prev_len;
    byte bits = ss->bits;
    int bits_left = ss->bits_left;
    int bytes_left = ss->bytes_left;
    int code_size = ss->code_size;
    int code_mask;
    int switch_code;
    int next_code = ss->next_code;
    lzw_decode *table = ss->table.decode;	/* constant pointer */
    lzw_decode *dc_next = table + next_code;	/* invariant */
    lzw_decode *dc;
    int code_escape = 1 << ss->InitialCodeLength;
    int eod = code_eod;
    bool low_order = ss->FirstBitLowOrder;
    uint len;
    int c;
    byte b;
    byte *q1;

    if_debug2('w', "[w]process decode: code_size=%d next_code=%d\n",
	      code_size, next_code);
#define set_code_size()\
  code_mask = (1 << code_size) - 1,\
  switch_code = code_mask + 1 - ss->EarlyChange
    set_code_size();
    if (!ss->BlockData)
	bytes_left = rlimit - p + 2;	/* never stop for bytes_left */
    /* If we are in the middle of copying a string, */
    /* do some more now. */
    if (code >= 0) {
	int rlen = ss->copy_left;
	int wlen = wlimit - q;
	int n = len = min(rlen, wlen);

	c = code;
	ss->copy_left = rlen -= len;
	if_debug3('W', "[W]copying 0x%x, %d byte(s) out of %d left\n",
		  code, len, rlen + len);
	while (rlen)
	    c = table[c].prefix,
		rlen--;
	q1 = q += len;
	n = len;
	while (--n >= 0) {
	    *q1-- = (dc = &table[c])->datum;
	    c = dc->prefix;
	}
	if (ss->copy_left) {	/* more to do */
	    pw->ptr = q;
	    return 1;
	}
	ss->copy_code = -1;
	len = ss->copy_len;
	/* Retrieve the first byte of the code just copied. */
	if (c == eod) {		/* We just copied the entire code, */
	    /* so the byte we want is immediately available. */
	    b = q1[1];
	} else {		/* We have to scan to the beginning of the code. */
	    for (; c != eod; c = table[c].prefix)
		b = (byte) c;
	}
	goto add;
    }
  top:if (code_size > bits_left) {
	if (bytes_left == 0) {
	    if (p == rlimit)
		goto out;
	    bytes_left = *++p;
	    if_debug1('W', "[W]block count %d\n", bytes_left);
	    if (bytes_left == 0) {
		status = EOFC;
		goto out;
	    }
	    goto top;
	}
	if (low_order)
	    code = bits >> (8 - bits_left);
	else
	    code = (uint) bits << (code_size - bits_left);
	if (bits_left + 8 < code_size) {	/* Need 2 more data bytes */
	    if (bytes_left == 1) {
		if (rlimit - p < 3)
		    goto out;
		bytes_left = p[2];
		if_debug1('W', "[W]block count %d\n",
			  bytes_left);
		if (bytes_left == 0) {
		    status = EOFC;
		    goto out;
		}
		bytes_left++;
		bits = p[1];
		p++;
	    } else {
		if (rlimit - p < 2)
		    goto out;
		bits = p[1];
	    }
	    if (low_order)
		code += (uint) bits << bits_left;
	    else
		code += (uint) bits << (code_size - 8 - bits_left);
	    bits_left += 8;
	    bits = p[2];
	    p += 2;
	    bytes_left -= 2;
	} else {
	    if (p == rlimit)
		goto out;
	    bits = *++p;
	    bytes_left--;
	}
	if (low_order)
	    code += (uint) bits << bits_left,
		bits_left += 8 - code_size;
	else
	    bits_left += 8 - code_size,
		code += bits >> bits_left;
    } else {
	if (low_order)
	    code = bits >> (8 - bits_left),
		bits_left -= code_size;
	else
	    bits_left -= code_size,
		code = bits >> bits_left;
    }
    code &= code_mask;
    if_debug2('W', "[W]reading 0x%x,%d\n", code, code_size);
    /*
     * There is an anomalous case where a code S is followed
     * immediately by another occurrence of the S string.
     * In this case, the next available code will be defined as
     * S followed by the first character of S, and will be
     * emitted immediately after the code S.  We have to
     * recognize this case specially, by noting that the code is
     * equal to next_code.
     */
    if (code >= next_code) {
	if (code > next_code) {
#ifdef DEBUG
	    lprintf2("[W]code = %d > next_code = %d\n",
		     code, next_code);
#endif
	    status = ERRC;
	    goto out;
	}
	/* Fabricate the entry for the code.  It will be */
	/* overwritten immediately, of course. */
	for (c = prev_code; c != eod; c = table[c].prefix)
	    dc_next->datum = c;
	len = prev_len + 1;
	dc_next->len = min(len, 255);
	dc_next->prefix = prev_code;
	if_debug3('w', "[w]decoding anomalous 0x%x=0x%x+%c\n",
		  next_code, prev_code, dc_next->datum);
    }
    /* See if there is enough room for the code. */
    len = table[code].len;
    if (len == 255) {		/* Check for special code (reset or end). */
	/* We set their lengths to 255 to avoid doing */
	/* an extra check in the normal case. */
	if (code == code_reset) {
	    if_debug1('w', "[w]reset: next_code was %d\n",
		      next_code);
	    next_code = code_0;
	    dc_next = table + code_0;
	    code_size = ss->InitialCodeLength + 1;
	    set_code_size();
	    prev_code = -1;
	    goto top;
	} else if (code == eod) {
	    status = EOFC;
	    goto out;
	}
	/* The code length won't fit in a byte, */
	/* compute it the hard way. */
	for (c = code, len = 0; c != eod; len++)
	    c = table[c].prefix;
	if_debug2('w', "[w]long code %d, length=%d\n", code, len);
    }
    if (wlimit - q < len) {
	ss->copy_code = code;
	ss->copy_left = ss->copy_len = len;
	status = 1;
	goto out;
    }
    /* Copy the string to the buffer (back to front). */
    /* Optimize for short codes, which are the most frequent. */
    dc = &table[code];
    switch (len) {
	default:
	    {
		byte *q1 = q += len;

		c = code;
		do {
		    *q1-- = (dc = &table[c])->datum;
		}
		while ((c = dc->prefix) != eod);
		b = q1[1];
	    }
	    break;
	case 3:
	    q[3] = dc->datum;
	    dc = &table[dc->prefix];
	case 2:
	    q[2] = dc->datum;
	    dc = &table[dc->prefix];
	case 1:
	    q[1] = b = dc->datum;
	    q += len;
    }
  add:				/* Add a new entry to the table */
    if (prev_code >= 0) {	/* Unfortunately, we have to check for next_code == */
	/* lzw_decode_max every time: just checking at power */
	/* of 2 boundaries stops us one code too soon. */
	if (next_code == lzw_decode_max) {
	    status = ERRC;
	    goto out;
	}
	dc_next->datum = b;	/* added char of string */
	dc_next->len = min(prev_len, 254) + 1;
	dc_next->prefix = prev_code;
	dc_next++;
	if_debug4('W', "[W]adding 0x%x=0x%x+%c(%d)\n",
		  next_code, prev_code, b, min(len, 255));
	if (++next_code == switch_code) {	/* Crossed a power of 2. */
	    /* We have to make a strange special check for */
	    /* reaching the end of the code space. */
	    if (next_code < lzw_decode_max - 1) {
		code_size++;
		set_code_size();
		if_debug2('w', "[w]crossed power of 2: new code_size=%d, next_code=%d\n",
			  code_size, next_code);
	    }
	}
    }
    prev_code = code;
    prev_len = len;
    goto top;
  out:pr->ptr = p;
    pw->ptr = q;
    ss->code_size = code_size;
    ss->prev_code = prev_code;
    ss->prev_len = prev_len;
    ss->bits = bits;
    ss->bits_left = bits_left;
    ss->bytes_left = bytes_left;
    ss->next_code = next_code;
    if_debug3('w', "[w]decoded %d bytes, prev_code=%d, next_code=%d\n",
	      (int)(q - q0), prev_code, next_code);
    return status;
}

#undef ss

/* Stream template */
const stream_template s_LZWD_template =
{&st_LZW_state, s_LZWD_init, s_LZWD_process, 3, 1, s_LZW_release,
 s_LZW_set_defaults, s_LZWD_reset
};