/* 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 <cworth@cworth.org>
*/
#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;
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)) {
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<<LZW_BITS_MAX)
#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;
}