Merge LZX compression updates

[wimlib] / src / lzx_common.c

diff --git a/src/lzx_common.c b/src/lzx_common.c
index bd2e097fe7e26fd5832537ac8f6bcc708dcc990f..0993f60756d869dccad03a17ed54714f77a32056 100644 (file)
--- a/src/lzx_common.c
+++ b/src/lzx_common.c
@@ -3,7 +3,7 @@
  */
 
 /*
- * Copyright (C) 2012, 2013, 2014 Eric Biggers
+ * Copyright (C) 2012, 2013, 2014, 2015 Eric Biggers
  *
  * This file is free software; you can redistribute it and/or modify it under
  * the terms of the GNU Lesser General Public License as published by the Free
@@ -41,7 +41,7 @@
 
 /* Mapping: offset slot => first match offset that uses that offset slot.
  */
-const u32 lzx_offset_slot_base[LZX_MAX_OFFSET_SLOTS] = {
+const u32 lzx_offset_slot_base[LZX_MAX_OFFSET_SLOTS + 1] = {
        0      , 1      , 2      , 3      , 4      ,    /* 0  --- 4  */
        6      , 8      , 12     , 16     , 24     ,    /* 5  --- 9  */
        32     , 48     , 64     , 96     , 128    ,    /* 10 --- 14 */
@@ -52,12 +52,12 @@ const u32 lzx_offset_slot_base[LZX_MAX_OFFSET_SLOTS] = {
        196608 , 262144 , 393216 , 524288 , 655360 ,    /* 35 --- 39 */
        786432 , 917504 , 1048576, 1179648, 1310720,    /* 40 --- 44 */
        1441792, 1572864, 1703936, 1835008, 1966080,    /* 45 --- 49 */
-       2097152                                         /* 50        */
+       2097152                                         /* extra     */
 };
 
 /* Mapping: offset slot => how many extra bits must be read and added to the
  * corresponding offset slot base to decode the match offset.  */
-const u8 lzx_extra_offset_bits[LZX_MAX_OFFSET_SLOTS] = {
+const u8 lzx_extra_offset_bits[LZX_MAX_OFFSET_SLOTS + 1] = {
        0 , 0 , 0 , 0 , 1 ,
        1 , 2 , 2 , 3 , 3 ,
        4 , 4 , 5 , 5 , 6 ,
@@ -71,60 +71,45 @@ const u8 lzx_extra_offset_bits[LZX_MAX_OFFSET_SLOTS] = {
        17
 };
 
-/* Round the specified compression block size (not LZX block size) up to the
- * next valid LZX window size, and return its order (log2).  Or, if the block
- * size is 0 or greater than the largest valid LZX window size, return 0.  */
+/* Round the specified buffer size up to the next valid LZX window size, and
+ * return its order (log2).  Or, if the buffer size is 0 or greater than the
+ * largest valid LZX window size, return 0.  */
 unsigned
-lzx_get_window_order(size_t max_block_size)
+lzx_get_window_order(size_t max_bufsize)
 {
        unsigned order;
 
-       if (max_block_size == 0 || max_block_size > LZX_MAX_WINDOW_SIZE)
+       if (max_bufsize == 0 || max_bufsize > LZX_MAX_WINDOW_SIZE)
                return 0;
 
-       order = fls32(max_block_size);
+       order = fls32(max_bufsize);
 
-       if (((u32)1 << order) != max_block_size)
+       if (((u32)1 << order) != max_bufsize)
                order++;
 
        return max(order, LZX_MIN_WINDOW_ORDER);
 }
 
+unsigned
+lzx_get_num_offset_slots(unsigned window_order)
+{
+       /* Note: one would expect that the maximum match offset would be
+        * 'window_size - LZX_MIN_MATCH_LEN', which would occur if the first two
+        * bytes were to match the last two bytes.  However, the format
+        * disallows this case.  This reduces the number of needed offset slots
+        * by 1.  */
+       u32 window_size = (u32)1 << window_order;
+       u32 max_offset = window_size - LZX_MIN_MATCH_LEN - 1;
+       return 1 + lzx_get_offset_slot(max_offset);
+}
+
 /* Given a valid LZX window order, return the number of symbols that will exist
  * in the main Huffman code.  */
 unsigned
 lzx_get_num_main_syms(unsigned window_order)
 {
-       u32 window_size = (u32)1 << window_order;
-
-       /* NOTE: the calculation *should* be as follows:
-        *
-        * u32 max_offset = window_size - LZX_MIN_MATCH_LEN;
-        * u32 max_adjusted_offset = max_offset + LZX_OFFSET_OFFSET;
-        * u32 num_offset_slots = 1 + lzx_get_offset_slot_raw(max_adjusted_offset);
-        *
-        * However since LZX_MIN_MATCH_LEN == LZX_OFFSET_OFFSET, we would get
-        * max_adjusted_offset == window_size, which would bump the number of
-        * offset slots up by 1 since every valid LZX window size is equal to a
-        * offset slot base value.  The format doesn't do this, and instead
-        * disallows matches with minimum length and maximum offset.  This sets
-        * max_adjusted_offset = window_size - 1, so instead we must calculate:
-        *
-        * num_offset_slots = 1 + lzx_get_offset_slot_raw(window_size - 1);
-        *
-        * ... which is the same as
-        *
-        * num_offset_slots = lzx_get_offset_slot_raw(window_size);
-        *
-        * ... since every valid window size is equal to an offset base value.
-        */
-       unsigned num_offset_slots = lzx_get_offset_slot_raw(window_size);
-
-       /* Now calculate the number of main symbols as LZX_NUM_CHARS literal
-        * symbols, plus 8 symbols per offset slot (since there are 8 possible
-        * length headers, and we need all (offset slot, length header)
-        * combinations).  */
-       return LZX_NUM_CHARS + (num_offset_slots << 3);
+       return LZX_NUM_CHARS + (lzx_get_num_offset_slots(window_order) *
+                               LZX_NUM_LEN_HEADERS);
 }
 
 static void