LZX decompression cleanups

[wimlib] / src / lzx-compress.c

diff --git a/src/lzx-compress.c b/src/lzx-compress.c
index b18004684658addcad9575df430bb4332af71bfd..81a6256eb7e8a88c67e6a6e091bd9f4131c34efe 100644 (file)
--- a/src/lzx-compress.c
+++ b/src/lzx-compress.c
@@ -127,17 +127,6 @@ static u32 lzx_record_literal(u8 literal, void *__main_freq_tab)
        return literal;
 }
 
-/* Equivalent to lzx_extra_bits[position_slot] except position_slot must be
- * between 2 and 37 */
-static inline unsigned lzx_get_num_extra_bits(unsigned position_slot)
-{
-#if 0
-       return lzx_extra_bits[position_slot];
-#endif
-       wimlib_assert(position_slot >= 2 && position_slot <= 37);
-       return (position_slot >> 1) - 1;
-}
-
 /* Constructs a match from an offset and a length, and updates the LRU queue and
  * the frequency of symbols in the main, length, and aligned offset alphabets.
  * The return value is a 32-bit number that provides the match in an
@@ -320,7 +309,7 @@ static int lzx_write_match(struct output_bitstream *out, int block_type,
 
        wimlib_assert(position_slot < LZX_NUM_POSITION_SLOTS);
 
-       num_extra_bits = lzx_extra_bits[position_slot];
+       num_extra_bits = lzx_get_num_extra_bits(position_slot);
 
        /* For aligned offset blocks with at least 3 extra bits, output the
         * verbatim bits literally, then the aligned bits encoded using the
@@ -596,41 +585,37 @@ static void lzx_make_huffman_codes(const struct lzx_freq_tables *freq_tabs,
                                        codes->aligned_codewords);
 }
 
-/* Do the 'E8' preprocessing, where the targets of x86 CALL instructions were
- * changed from relative offsets to absolute offsets.  This type of
- * preprocessing can be used on any binary data even if it is not actually
- * machine code.  It seems to always be used in WIM files, even though there is
- * no bit to indicate that it actually is used, unlike in the LZX compressed
- * format as used in other file formats such as the cabinet format, where a bit
- * is reserved for that purpose. */
-static void do_call_insn_preprocessing(u8 uncompressed_data[],
-                                      unsigned uncompressed_data_len)
+static void do_call_insn_translation(u32 *call_insn_target, int input_pos,
+                                    int32_t file_size)
 {
-       int i = 0;
-       int file_size = LZX_MAGIC_FILESIZE;
-       int32_t rel_offset;
        int32_t abs_offset;
+       int32_t rel_offset;
 
-       /* Not enabled in the last 6 bytes, which means the 5-byte call
-        * instruction cannot start in the last *10* bytes. */
-       while (i < uncompressed_data_len - 10) {
-               if (uncompressed_data[i] != 0xe8) {
-                       i++;
-                       continue;
+       rel_offset = le32_to_cpu(*call_insn_target);
+       if (rel_offset >= -input_pos && rel_offset < file_size) {
+               if (rel_offset < file_size - input_pos) {
+                       /* "good translation" */
+                       abs_offset = rel_offset + input_pos;
+               } else {
+                       /* "compensating translation" */
+                       abs_offset = rel_offset - file_size;
                }
-               rel_offset = le32_to_cpu(*(int32_t*)(uncompressed_data + i + 1));
-
-               if (rel_offset >= -i && rel_offset < file_size) {
-                       if (rel_offset < file_size - i) {
-                               /* "good translation" */
-                               abs_offset = rel_offset + i;
-                       } else {
-                               /* "compensating translation" */
-                               abs_offset = rel_offset - file_size;
-                       }
-                       *(int32_t*)(uncompressed_data + i + 1) = cpu_to_le32(abs_offset);
+               *call_insn_target = cpu_to_le32(abs_offset);
+       }
+}
+
+/* This is the reverse of undo_call_insn_preprocessing() in lzx-decompress.c.
+ * See the comment above that function for more information. */
+static void do_call_insn_preprocessing(u8 uncompressed_data[],
+                                      int uncompressed_data_len)
+{
+       for (int i = 0; i < uncompressed_data_len - 10; i++) {
+               if (uncompressed_data[i] == 0xe8) {
+                       do_call_insn_translation((u32*)&uncompressed_data[i + 1],
+                                                i,
+                                                LZX_WIM_MAGIC_FILESIZE);
+                       i += 4;
                }
-               i += 5;
        }
 }
 
@@ -670,7 +655,7 @@ int lzx_compress(const void *__uncompressed_data, unsigned uncompressed_len,
                 void *compressed_data, unsigned *compressed_len_ret)
 {
        struct output_bitstream ostream;
-       u8 uncompressed_data[uncompressed_len + LZX_MAX_MATCH];
+       u8 uncompressed_data[uncompressed_len + 8];
        struct lzx_freq_tables freq_tabs;
        struct lzx_codes codes;
        u32 match_tab[uncompressed_len];