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/* cairo - a vector graphics library with display and print output

 *

 * Copyright © 2006 Red Hat, Inc.

 *

 * This library is free software; you can redistribute it and/or

 * modify it either under the terms of the GNU Lesser General Public

 * License version 2.1 as published by the Free Software Foundation

 * (the "LGPL") or, at your option, under the terms of the Mozilla

 * Public License Version 1.1 (the "MPL"). If you do not alter this

 * notice, a recipient may use your version of this file under either

 * the MPL or the LGPL.

 *

 * You should have received a copy of the LGPL along with this library

 * in the file COPYING-LGPL-2.1; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Suite 500, Boston, MA 02110-1335, USA

 * You should have received a copy of the MPL along with this library

 * in the file COPYING-MPL-1.1

 *

 * The contents of this file are subject to the Mozilla Public License

 * Version 1.1 (the "License"); you may not use this file except in

 * compliance with the License. You may obtain a copy of the License at

 * http://www.mozilla.org/MPL/

 *

 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY

 * OF ANY KIND, either express or implied. See the LGPL or the MPL for

 * the specific language governing rights and limitations.

 *

 * The Original Code is the cairo graphics library.

 *

 * The Initial Developer of the Original Code is University of Southern

 * California.

 *

 * Contributor(s):

 *	Carl D. Worth 

 */

#include "cairoint.h"

#include "cairo-error-private.h"

typedef struct _lzw_buf {

    cairo_status_t status;

    unsigned char *data;

    int data_size;

    int num_data;

    uint32_t pending;

    unsigned int pending_bits;

} lzw_buf_t;

/* An lzw_buf_t is a simple, growable chunk of memory for holding

 * variable-size objects of up to 16 bits each.

 *

 * Initialize an lzw_buf_t to the given size in bytes.

 *

 * To store objects into the lzw_buf_t, call _lzw_buf_store_bits and

 * when finished, call _lzw_buf_store_pending, (which flushes out the

 * last few bits that hadn't yet made a complete byte yet).

 *

 * Instead of returning failure from any functions, lzw_buf_t provides

 * a status value that the caller can query, (and should query at

 * least once when done with the object). The status value will be

 * either %CAIRO_STATUS_SUCCESS or %CAIRO_STATUS_NO_MEMORY;

 */

static void

_lzw_buf_init (lzw_buf_t *buf, int size)

{

    if (size == 0)

	size = 16;

    buf->status = CAIRO_STATUS_SUCCESS;

    buf->data_size = size;

    buf->num_data = 0;

    buf->pending = 0;

    buf->pending_bits = 0;

    buf->data = malloc (size);

    if (unlikely (buf->data == NULL)) {

	buf->data_size = 0;

	buf->status = _cairo_error (CAIRO_STATUS_NO_MEMORY);

	return;

    }

}

/* Increase the buffer size by doubling.

 *

 * Returns %CAIRO_STATUS_SUCCESS or %CAIRO_STATUS_NO_MEMORY

 */

static cairo_status_t

_lzw_buf_grow (lzw_buf_t *buf)

{

    int new_size = buf->data_size * 2;

    unsigned char *new_data;

    if (buf->status)

	return buf->status;

    new_data = NULL;

    /* check for integer overflow */

    if (new_size / 2 == buf->data_size)

	new_data = realloc (buf->data, new_size);

    if (unlikely (new_data == NULL)) {

	free (buf->data);

	buf->data_size = 0;

	buf->status = _cairo_error (CAIRO_STATUS_NO_MEMORY);

	return buf->status;

    }

    buf->data = new_data;

    buf->data_size = new_size;

    return CAIRO_STATUS_SUCCESS;

}

/* Store the lowest num_bits bits of values into buf.

 *

 * Note: The bits of value above size_in_bits must be 0, (so don't lie

 * about the size).

 *

 * See also _lzw_buf_store_pending which must be called after the last

 * call to _lzw_buf_store_bits.

 *

 * Sets buf->status to either %CAIRO_STATUS_SUCCESS or %CAIRO_STATUS_NO_MEMORY.

 */

static void

_lzw_buf_store_bits (lzw_buf_t *buf, uint16_t value, int num_bits)

{

    cairo_status_t status;

    assert (value <= (1 << num_bits) - 1);

    if (buf->status)

	return;

    buf->pending = (buf->pending << num_bits) | value;

    buf->pending_bits += num_bits;

    while (buf->pending_bits >= 8) {

	if (buf->num_data >= buf->data_size) {

	    status = _lzw_buf_grow (buf);

	    if (unlikely (status))

		return;

	}

	buf->data[buf->num_data++] = buf->pending >> (buf->pending_bits - 8);

	buf->pending_bits -= 8;

    }

}

/* Store the last remaining pending bits into the buffer.

 *

 * Note: This function must be called after the last call to

 * _lzw_buf_store_bits.

 *

 * Sets buf->status to either %CAIRO_STATUS_SUCCESS or %CAIRO_STATUS_NO_MEMORY.

 */

static void

_lzw_buf_store_pending  (lzw_buf_t *buf)

{

    cairo_status_t status;

    if (buf->status)

	return;

    if (buf->pending_bits == 0)

	return;

    assert (buf->pending_bits < 8);

    if (buf->num_data >= buf->data_size) {

	status = _lzw_buf_grow (buf);

	if (unlikely (status))

	    return;

    }

    buf->data[buf->num_data++] = buf->pending << (8 - buf->pending_bits);

    buf->pending_bits = 0;

}

/* LZW defines a few magic code values */

#define LZW_CODE_CLEAR_TABLE	256

#define LZW_CODE_EOD		257

#define LZW_CODE_FIRST		258

/* We pack three separate values into a symbol as follows:

 *

 * 12 bits (31 down to 20):	CODE: code value used to represent this symbol

 * 12 bits (19 down to  8):	PREV: previous code value in chain

 *  8 bits ( 7 down to  0):	NEXT: next byte value in chain

 */

typedef uint32_t lzw_symbol_t;

#define LZW_SYMBOL_SET(sym, prev, next)			((sym) = ((prev) << 8)|(next))

#define LZW_SYMBOL_SET_CODE(sym, code, prev, next)	((sym) = ((code << 20)|(prev) << 8)|(next))

#define LZW_SYMBOL_GET_CODE(sym)			(((sym) >> 20))

#define LZW_SYMBOL_GET_PREV(sym)			(((sym) >>  8) & 0x7ff)

#define LZW_SYMBOL_GET_BYTE(sym)			(((sym) >>  0) & 0x0ff)

/* The PREV+NEXT fields can be seen as the key used to fetch values

 * from the hash table, while the code is the value fetched.

 */

#define LZW_SYMBOL_KEY_MASK	0x000fffff

/* Since code values are only stored starting with 258 we can safely

 * use a zero value to represent free slots in the hash table. */

#define LZW_SYMBOL_FREE		0x00000000

/* These really aren't very free for modifying. First, the PostScript

 * specification sets the 9-12 bit range. Second, the encoding of

 * lzw_symbol_t above also relies on 2 of LZW_BITS_MAX plus one byte

 * fitting within 32 bits.

 *

 * But other than that, the LZW compression scheme could function with

 * more bits per code.

 */

#define LZW_BITS_MIN		9

#define LZW_BITS_MAX		12

#define LZW_BITS_BOUNDARY(bits)	((1<<(bits))-1)

#define LZW_MAX_SYMBOLS		(1<

#define LZW_SYMBOL_TABLE_SIZE	9013

#define LZW_SYMBOL_MOD1		LZW_SYMBOL_TABLE_SIZE

#define LZW_SYMBOL_MOD2		9011

typedef struct _lzw_symbol_table {

    lzw_symbol_t table[LZW_SYMBOL_TABLE_SIZE];

} lzw_symbol_table_t;

/* Initialize the hash table to entirely empty */

static void

_lzw_symbol_table_init (lzw_symbol_table_t *table)

{

    memset (table->table, 0, LZW_SYMBOL_TABLE_SIZE * sizeof (lzw_symbol_t));

}

/* Lookup a symbol in the symbol table. The PREV and NEXT fields of

 * symbol form the key for the lookup.

 *

 * If successful, then this function returns %TRUE and slot_ret will be

 * left pointing at the result that will have the CODE field of

 * interest.

 *

 * If the lookup fails, then this function returns %FALSE and slot_ret

 * will be pointing at the location in the table to which a new CODE

 * value should be stored along with PREV and NEXT.

 */

static cairo_bool_t

_lzw_symbol_table_lookup (lzw_symbol_table_t	 *table,

			  lzw_symbol_t		  symbol,

			  lzw_symbol_t		**slot_ret)

{

    /* The algorithm here is identical to that in cairo-hash.c. We

     * copy it here to allow for a rather more efficient

     * implementation due to several circumstances that do not apply

     * to the more general case:

     *

     * 1) We have a known bound on the total number of symbols, so we

     *    have a fixed-size table without any copying when growing

     *

     * 2) We never delete any entries, so we don't need to

     *    support/check for DEAD entries during lookup.

     *

     * 3) The object fits in 32 bits so we store each object in its

     *    entirety within the table rather than storing objects

     *    externally and putting pointers in the table, (which here

     *    would just double the storage requirements and have negative

     *    impacts on memory locality).

     */

    int i, idx, step, hash = symbol & LZW_SYMBOL_KEY_MASK;

    lzw_symbol_t candidate;

    idx = hash % LZW_SYMBOL_MOD1;

    step = 0;

    *slot_ret = NULL;

    for (i = 0; i < LZW_SYMBOL_TABLE_SIZE; i++)

    {

	candidate = table->table[idx];

	if (candidate == LZW_SYMBOL_FREE)

	{

	    *slot_ret = &table->table[idx];

	    return FALSE;

	}

	else /* candidate is LIVE */

	{

	    if ((candidate & LZW_SYMBOL_KEY_MASK) ==

		(symbol & LZW_SYMBOL_KEY_MASK))

	    {

		*slot_ret = &table->table[idx];

		return TRUE;

	    }

	}

	if (step == 0) {

	    step = hash % LZW_SYMBOL_MOD2;

	    if (step == 0)

		step = 1;

	}

	idx += step;

	if (idx >= LZW_SYMBOL_TABLE_SIZE)

	    idx -= LZW_SYMBOL_TABLE_SIZE;

    }

    return FALSE;

}

/* Compress a bytestream using the LZW algorithm.

 *

 * This is an original implementation based on reading the

 * specification of the LZWDecode filter in the PostScript Language

 * Reference. The free parameters in the LZW algorithm are set to the

 * values mandated by PostScript, (symbols encoded with widths from 9

 * to 12 bits).

 *

 * This function returns a pointer to a newly allocated buffer holding

 * the compressed data, or %NULL if an out-of-memory situation

 * occurs.

 *

 * Notice that any one of the _lzw_buf functions called here could

 * trigger an out-of-memory condition. But lzw_buf_t uses cairo's

 * shutdown-on-error idiom, so it's safe to continue to call into

 * lzw_buf without having to check for errors, (until a final check at

 * the end).

 */

unsigned char *

_cairo_lzw_compress (unsigned char *data, unsigned long *size_in_out)

{

    int bytes_remaining = *size_in_out;

    lzw_buf_t buf;

    lzw_symbol_table_t table;

    lzw_symbol_t symbol, *slot = NULL; /* just to squelch a warning */

    int code_next = LZW_CODE_FIRST;

    int code_bits = LZW_BITS_MIN;

    int prev, next = 0; /* just to squelch a warning */

    if (*size_in_out == 0)

	return NULL;

    _lzw_buf_init (&buf, *size_in_out);

    _lzw_symbol_table_init (&table);

    /* The LZW header is a clear table code. */

    _lzw_buf_store_bits (&buf, LZW_CODE_CLEAR_TABLE, code_bits);

    while (1) {

	/* Find the longest existing code in the symbol table that

	 * matches the current input, if any. */

	prev = *data++;

	bytes_remaining--;

	if (bytes_remaining) {

	    do

	    {

		next = *data++;

		bytes_remaining--;

		LZW_SYMBOL_SET (symbol, prev, next);

		if (_lzw_symbol_table_lookup (&table, symbol, &slot))

		    prev = LZW_SYMBOL_GET_CODE (*slot);

	    } while (bytes_remaining && *slot != LZW_SYMBOL_FREE);

	    if (*slot == LZW_SYMBOL_FREE) {

		data--;

		bytes_remaining++;

	    }

	}

	/* Write the code into the output. This is either a byte read

	 * directly from the input, or a code from the last successful

	 * lookup. */

	_lzw_buf_store_bits (&buf, prev, code_bits);

	if (bytes_remaining == 0)

	    break;

	LZW_SYMBOL_SET_CODE (*slot, code_next++, prev, next);

	if (code_next > LZW_BITS_BOUNDARY(code_bits))

	{

	    code_bits++;

	    if (code_bits > LZW_BITS_MAX) {

		_lzw_symbol_table_init (&table);

		_lzw_buf_store_bits (&buf, LZW_CODE_CLEAR_TABLE, code_bits - 1);

		code_bits = LZW_BITS_MIN;

		code_next = LZW_CODE_FIRST;

	    }

	}

    }

    /* The LZW footer is an end-of-data code. */

    _lzw_buf_store_bits (&buf, LZW_CODE_EOD, code_bits);

    _lzw_buf_store_pending (&buf);

    /* See if we ever ran out of memory while writing to buf. */

    if (buf.status == CAIRO_STATUS_NO_MEMORY) {

	*size_in_out = 0;

	return NULL;

    }

    assert (buf.status == CAIRO_STATUS_SUCCESS);

    *size_in_out = buf.num_data;

    return buf.data;

}