A few minor compressor cleanups

[wimlib] / src / lzx-common.c

diff --git a/src/lzx-common.c b/src/lzx-common.c
index b2eeb7d1e54f1bbdfcabbae8d708ff8fd7e220d4..d733ada7d8d073b76a86fc2a041de0154d835e81 100644 (file)
--- a/src/lzx-common.c
+++ b/src/lzx-common.c
@@ -33,9 +33,9 @@
 #  include <emmintrin.h>
 #endif
 
-/* Mapping: position slot => first match offset that uses that position slot.
+/* Mapping: offset slot => first match offset that uses that offset slot.
  */
-const u32 lzx_position_base[LZX_MAX_POSITION_SLOTS] = {
+const u32 lzx_offset_slot_base[LZX_MAX_OFFSET_SLOTS] = {
        0      , 1      , 2      , 3      , 4      ,    /* 0  --- 4  */
        6      , 8      , 12     , 16     , 24     ,    /* 5  --- 9  */
        32     , 48     , 64     , 96     , 128    ,    /* 10 --- 14 */
@@ -49,10 +49,9 @@ const u32 lzx_position_base[LZX_MAX_POSITION_SLOTS] = {
        2097152                                         /* 50        */
 };
 
-/* Mapping: position slot => how many extra bits must be read and added to the
- * corresponding position base to decode the match offset.  */
-#ifdef USE_LZX_EXTRA_BITS_ARRAY
-const u8 lzx_extra_bits[LZX_MAX_POSITION_SLOTS] = {
+/* 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] = {
        0 , 0 , 0 , 0 , 1 ,
        1 , 2 , 2 , 3 , 3 ,
        4 , 4 , 5 , 5 , 6 ,
@@ -65,53 +64,61 @@ const u8 lzx_extra_bits[LZX_MAX_POSITION_SLOTS] = {
        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)
+/* 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.  */
+unsigned
+lzx_get_window_order(size_t max_block_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);
+       unsigned order;
+
+       if (max_block_size == 0 || max_block_size > LZX_MAX_WINDOW_SIZE)
+               return 0;
+
+       order = bsr32(max_block_size);
+
+       if (((u32)1 << order) != max_block_size)
+               order++;
+
+       return max(order, LZX_MIN_WINDOW_ORDER);
 }
 
-/* Given a valid LZX window size, return the number of symbols that will exist
+/* 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(u32 window_size)
+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_formatted_offset = max_offset + LZX_OFFSET_OFFSET;
-        * u32 num_position_slots = 1 + lzx_get_position_slot_raw(max_formatted_offset);
+        * 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_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
+        * 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_formatted_offset = window_size - 1, so instead we must calculate:
+        * max_adjusted_offset = window_size - 1, so instead we must calculate:
         *
-        * num_position_slots = 1 + lzx_get_position_slot_raw(window_size - 1);
+        * num_offset_slots = 1 + lzx_get_offset_slot_raw(window_size - 1);
         *
         * ... which is the same as
         *
-        * num_position_slots = lzx_get_position_slot_raw(window_size);
+        * num_offset_slots = lzx_get_offset_slot_raw(window_size);
         *
-        * ... since every valid window size is equal to a position base value.
+        * ... since every valid window size is equal to an offset base value.
         */
-       unsigned num_position_slots = lzx_get_position_slot_raw(window_size);
+       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 position slot (since there are 8 possible
-        * length headers, and we need all (position slot, length header)
+        * 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_position_slots << 3);
+       return LZX_NUM_CHARS + (num_offset_slots << 3);
 }
 
 static void