Variable LZX window sizes

[wimlib] / src / lzx-common.c

diff --git a/src/lzx-common.c b/src/lzx-common.c
index dfd6256b71b3396db6d7d7f847f826ae6482622d..547059e7b93268c8cc9af73e635ada28ec5594fa 100644 (file)
--- a/src/lzx-common.c
+++ b/src/lzx-common.c
@@ -26,8 +26,8 @@
 #endif
 
 #include "wimlib/lzx.h"
+#include "wimlib/util.h"
 
-#ifdef USE_LZX_EXTRA_BITS_ARRAY
 /* LZX uses what it calls 'position slots' to represent match offsets.
  * What this means is that a small 'position slot' number and a small
  * offset from that slot are encoded instead of one large offset for
@@ -35,7 +35,23 @@
  * - 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[] = {
+
+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        */
+};
+
+#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 ,
@@ -50,17 +66,24 @@ const u8 lzx_extra_bits[] = {
 };
 #endif
 
-const u32 lzx_position_base[] = {
-       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
-};
+/* LZX window size can be between 2^15 and 2^21, inclusively.  */
+bool
+lzx_window_size_valid(u32 window_size)
+{
+       if (window_size == 0)
+               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 the specified valid window size, return the number of LZX main symbols
+ * that will be needed.  (This depends on the number of position slots, which
+ * itself depends on the window size.)  */
+unsigned
+lzx_get_num_main_syms(u32 window_size)
+{
+       unsigned num_position_slots = lzx_get_position_slot_raw(window_size);
+       return LZX_NUM_CHARS + (num_position_slots << 3);
+}