+
+static void
+do_translate_target(s32 *target, s32 input_pos)
+{
+ s32 abs_offset, rel_offset;
+
+ /* XXX: This assumes unaligned memory accesses are okay. */
+ rel_offset = le32_to_cpu(*target);
+ if (rel_offset >= -input_pos && rel_offset < LZX_WIM_MAGIC_FILESIZE) {
+ if (rel_offset < LZX_WIM_MAGIC_FILESIZE - input_pos) {
+ /* "good translation" */
+ abs_offset = rel_offset + input_pos;
+ } else {
+ /* "compensating translation" */
+ abs_offset = rel_offset - LZX_WIM_MAGIC_FILESIZE;
+ }
+ *target = cpu_to_le32(abs_offset);
+ }
+}
+
+static void
+undo_translate_target(s32 *target, s32 input_pos)
+{
+ s32 abs_offset, rel_offset;
+
+ /* XXX: This assumes unaligned memory accesses are okay. */
+ abs_offset = le32_to_cpu(*target);
+ if (abs_offset >= 0) {
+ if (abs_offset < LZX_WIM_MAGIC_FILESIZE) {
+ /* "good translation" */
+ rel_offset = abs_offset - input_pos;
+
+ *target = cpu_to_le32(rel_offset);
+ }
+ } else {
+ if (abs_offset >= -input_pos) {
+ /* "compensating translation" */
+ rel_offset = abs_offset + LZX_WIM_MAGIC_FILESIZE;
+
+ *target = cpu_to_le32(rel_offset);
+ }
+ }
+}
+
+/*
+ * Do or undo the 'E8' preprocessing used in LZX. Before compression, the
+ * uncompressed data is preprocessed by changing the targets of x86 CALL
+ * instructions from relative offsets to absolute offsets. After decompression,
+ * the translation is undone by changing the targets of x86 CALL instructions
+ * from absolute offsets to relative offsets.
+ *
+ * Note that despite its intent, E8 preprocessing can be done on any data even
+ * if it is not actually x86 machine code. In fact, E8 preprocessing appears to
+ * always be used in LZX-compressed resources in WIM files; there is no bit to
+ * indicate whether it is used or not, unlike in the LZX compressed format as
+ * used in cabinet files, where a bit is reserved for that purpose.
+ *
+ * E8 preprocessing is disabled in the last 6 bytes of the uncompressed data,
+ * which really means the 5-byte call instruction cannot start in the last 10
+ * bytes of the uncompressed data. This is one of the errors in the LZX
+ * documentation.
+ *
+ * E8 preprocessing does not appear to be disabled after the 32768th chunk of a
+ * WIM resource, which apparently is another difference from the LZX compression
+ * used in cabinet files.
+ *
+ * E8 processing is supposed to take the file size as a parameter, as it is used
+ * in calculating the translated jump targets. But in WIM files, this file size
+ * is always the same (LZX_WIM_MAGIC_FILESIZE == 12000000).
+ */
+static
+#ifndef __SSE2__
+inline /* Although inlining the 'process_target' function still speeds up the
+ SSE2 case, it bloats the binary more. */
+#endif
+void
+lzx_e8_filter(u8 *data, s32 size, void (*process_target)(s32 *, s32))
+{
+#ifdef __SSE2__
+ /* SSE2 vectorized implementation for x86_64. This speeds up LZX
+ * decompression by about 5-8% overall. (Usually --- the performance
+ * actually regresses slightly in the degenerate case that the data
+ * consists entirely of 0xe8 bytes. Also, this optimization affects
+ * compression as well, but the percentage improvement is less because
+ * LZX compression is much slower than LZX decompression. ) */
+ __m128i *p128 = (__m128i *)data;
+ u32 valid_mask = 0xFFFFFFFF;
+
+ if (size >= 32 && (uintptr_t)data % 16 == 0) {
+ __m128i * const end128 = p128 + size / 16 - 1;
+
+ /* Create a vector of all 0xe8 bytes */
+ const __m128i e8_bytes = _mm_set1_epi8(0xe8);
+
+ /* Iterate through the 16-byte vectors in the input. */
+ do {
+ /* Compare the current 16-byte vector with the vector of
+ * all 0xe8 bytes. This produces 0xff where the byte is
+ * 0xe8 and 0x00 where it is not. */
+ __m128i cmpresult = _mm_cmpeq_epi8(*p128, e8_bytes);
+
+ /* Map the comparison results into a single 16-bit
+ * number. It will contain a 1 bit when the
+ * corresponding byte in the current 16-byte vector is
+ * an e8 byte. Note: the low-order bit corresponds to
+ * the first (lowest address) byte. */
+ u32 e8_mask = _mm_movemask_epi8(cmpresult);
+
+ if (!e8_mask) {
+ /* If e8_mask is 0, then none of these 16 bytes
+ * have value 0xe8. No e8 translation is
+ * needed, and there is no restriction that
+ * carries over to the next 16 bytes. */
+ valid_mask = 0xFFFFFFFF;
+ } else {
+ /* At least one byte has value 0xe8.
+ *
+ * The AND with valid_mask accounts for the fact
+ * that we can't start an e8 translation that
+ * overlaps the previous one. */
+ while ((e8_mask &= valid_mask)) {
+
+ /* Count the number of trailing zeroes
+ * in e8_mask. This will produce the
+ * index of the byte, within the 16, at
+ * which the next e8 translation should
+ * be done. */
+ u32 bit = __builtin_ctz(e8_mask);
+
+ /* Do (or undo) the e8 translation. */
+ u8 *p8 = (u8 *)p128 + bit;
+ (*process_target)((s32 *)(p8 + 1),
+ p8 - data);
+
+ /* Don't start an e8 translation in the
+ * next 4 bytes. */
+ valid_mask &= ~((u32)0x1F << bit);
+ }
+ /* Moving on to the next vector. Shift and set
+ * valid_mask accordingly. */
+ valid_mask >>= 16;
+ valid_mask |= 0xFFFF0000;
+ }
+ } while (++p128 < end128);
+ }
+
+ u8 *p8 = (u8 *)p128;
+ while (!(valid_mask & 1)) {
+ p8++;
+ valid_mask >>= 1;
+ }
+#else /* __SSE2__ */
+ u8 *p8 = data;
+#endif /* !__SSE2__ */
+
+ if (size > 10) {
+ /* Finish any bytes that weren't processed by the vectorized
+ * implementation. */
+ u8 *p8_end = data + size - 10;
+ do {
+ if (*p8 == 0xe8) {
+ (*process_target)((s32 *)(p8 + 1), p8 - data);
+ p8 += 5;
+ } else {
+ p8++;
+ }
+ } while (p8 < p8_end);
+ }
+}
+
+void
+lzx_do_e8_preprocessing(u8 *data, s32 size)
+{
+ lzx_e8_filter(data, size, do_translate_target);
+}
+
+void
+lzx_undo_e8_preprocessing(u8 *data, s32 size)
+{
+ lzx_e8_filter(data, size, undo_translate_target);
+}
git://wimlib.net / wimlib / commitdiff