X-Git-Url: https://wimlib.net/git/?p=wimlib;a=blobdiff_plain;f=src%2Flzx-common.c;h=2fd54c1823e2552e691ca2355f4184559820f6bd;hp=8afe2abe0843e879aa9e13bdf4162ed727b2233a;hb=ced16a28e197645a40fa04a54793d117a04526d7;hpb=885632f08c75c1d7bb5d25436231c78f6ad7e0c0

diff --git a/src/lzx-common.c b/src/lzx-common.c
index 8afe2abe..2fd54c18 100644
--- a/src/lzx-common.c
+++ b/src/lzx-common.c
@@ -1,4 +1,32 @@
-#include "lzx.h"
+/*
+ * lzx-common.c - Common data for LZX compression and decompression.
+ */
+
+/*
+ * Copyright (C) 2012, 2013 Eric Biggers
+ *
+ * This file is part of wimlib, a library for working with WIM files.
+ *
+ * wimlib is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License as published by the Free
+ * Software Foundation; either version 3 of the License, or (at your option)
+ * any later version.
+ *
+ * wimlib is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ * A PARTICULAR PURPOSE. See the GNU General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with wimlib; if not, see http://www.gnu.org/licenses/.
+ */
+
+#ifdef HAVE_CONFIG_H
+#  include "config.h"
+#endif
+
+#include "wimlib/lzx.h"
+#include "wimlib/util.h"
 
 /* LZX uses what it calls 'position slots' to represent match offsets.
  * What this means is that a small 'position slot' number and a small
@@ -7,18 +35,80 @@
  * - lzx_position_base is an index to the position slot bases
  * - lzx_extra_bits states how many bits of offset-from-base data is needed.
  */
-const u8 lzx_extra_bits[51] = {
-	0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6,
-	7, 7, 8, 8, 9, 9, 10, 10, 11, 11, 12, 12, 13, 13, 14, 14,
-	15, 15, 16, 16, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17,
-	17, 17, 17
+
+const u32 lzx_position_base[LZX_MAX_POSITION_SLOTS] = {
+	0      , 1      , 2      , 3      , 4      ,	/* 0  --- 4  */
+	6      , 8      , 12     , 16     , 24     ,	/* 5  --- 9  */
+	32     , 48     , 64     , 96     , 128    ,    /* 10 --- 14 */
+	192    , 256    , 384    , 512    , 768    ,    /* 15 --- 19 */
+	1024   , 1536   , 2048   , 3072   , 4096   ,    /* 20 --- 24 */
+	6144   , 8192   , 12288  , 16384  , 24576  ,    /* 25 --- 29 */
+	32768  , 49152  , 65536  , 98304  , 131072 ,    /* 30 --- 34 */
+	196608 , 262144 , 393216 , 524288 , 655360 ,    /* 35 --- 39 */
+	786432 , 917504 , 1048576, 1179648, 1310720,    /* 40 --- 44 */
+	1441792, 1572864, 1703936, 1835008, 1966080,    /* 45 --- 49 */
+	2097152						/* 50	     */
 };
 
-const u32 lzx_position_base[51] = {
-	0, 1, 2, 3, 4, 6, 8, 12, 16, 24, 32, 48, 64, 96, 128, 192, 256, 384,
-	512, 768, 1024, 1536, 2048, 3072, 4096, 6144, 8192, 12288, 16384, 24576,
-	32768, 49152, 65536, 98304, 131072, 196608, 262144, 393216, 524288,
-	655360, 786432, 917504, 1048576, 1179648, 1310720, 1441792, 1572864,
-	1703936, 1835008, 1966080, 2097152
+#ifdef USE_LZX_EXTRA_BITS_ARRAY
+const u8 lzx_extra_bits[LZX_MAX_POSITION_SLOTS] = {
+	0 , 0 , 0 , 0 , 1 ,
+	1 , 2 , 2 , 3 , 3 ,
+	4 , 4 , 5 , 5 , 6 ,
+	6 , 7 , 7 , 8 , 8 ,
+	9 , 9 , 10, 10, 11,
+	11, 12, 12, 13, 13,
+	14, 14, 15, 15, 16,
+	16, 17, 17, 17, 17,
+	17, 17, 17, 17, 17,
+	17, 17, 17, 17, 17,
+	17
 };
+#endif
+
+/* LZX window size must be a power of 2 between 2^15 and 2^21, inclusively.  */
+bool
+lzx_window_size_valid(size_t window_size)
+{
+	if (window_size == 0 || (u32)window_size != window_size)
+		return false;
+	u32 order = bsr32(window_size);
+	if (window_size != 1U << order)
+		return false;
+	return (order >= LZX_MIN_WINDOW_ORDER && order <= LZX_MAX_WINDOW_ORDER);
+}
+
+/* Given a valid LZX window size, return the number of symbols that will exist
+ * in the main Huffman code.  */
+unsigned
+lzx_get_num_main_syms(u32 window_size)
+{
+	/* NOTE: the calculation *should* be as follows:
+	 *
+	 * u32 max_offset = window_size - LZX_MIN_MATCH_LEN;
+	 * u32 max_formatted_offset = max_offset + LZX_OFFSET_OFFSET;
+	 * u32 num_position_slots = 1 + lzx_get_position_slot_raw(max_formatted_offset);
+	 *
+	 * However since LZX_MIN_MATCH_LEN == LZX_OFFSET_OFFSET, we would get
+	 * max_formatted_offset == window_size, which would bump the number of
+	 * position slots up by 1 since every valid LZX window size is equal to
+	 * a position base value.  The format doesn't do this, and instead
+	 * disallows matches with minimum length and maximum offset.  This sets
+	 * max_formatted_offset = window_size - 1, so instead we must calculate:
+	 *
+	 * num_position_slots = 1 + lzx_get_position_slot_raw(window_size - 1);
+	 *
+	 * ... which is the same as
+	 *
+	 * num_position_slots = lzx_get_position_slot_raw(window_size);
+	 *
+	 * ... since every valid window size is equal to a position base value.
+	 */
+	unsigned num_position_slots = lzx_get_position_slot_raw(window_size);
 
+	/* Now calculate the number of main symbols as LZX_NUM_CHARS literal
+	 * symbols, plus 8 symbols per position slot (since there are 8 possible
+	 * length headers, and we need all (position slot, length header)
+	 * combinations).  */
+	return LZX_NUM_CHARS + (num_position_slots << 3);
+}