/* 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; 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<<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; }