X-Git-Url: https://wimlib.net/git/?a=blobdiff_plain;f=src%2Flzx-common.c;h=24bf9974c4ca5783c68c7f0ca0e4479fd23755dc;hb=af141a23c4d1540b8a64759bb68c7cd7ff054e72;hp=5f5228352381447c4a10c5d13998d71497b27134;hpb=883833a4b3dabec325edf1ca938000f91d587c00;p=wimlib diff --git a/src/lzx-common.c b/src/lzx-common.c index 5f522835..24bf9974 100644 --- a/src/lzx-common.c +++ b/src/lzx-common.c @@ -25,9 +25,14 @@ # include "config.h" #endif +#include "wimlib/endianness.h" #include "wimlib/lzx.h" #include "wimlib/util.h" +#ifdef __SSE2__ +# include +#endif + /* 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 @@ -78,12 +83,218 @@ lzx_window_size_valid(size_t window_size) 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.) */ +/* Given a valid LZX window size, return the number of symbols that will exist + * in the main Huffman code. */ unsigned lzx_get_num_main_syms(u32 window_size) { + /* 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); + * + * 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 + * disallows matches with minimum length and maximum offset. This sets + * max_formatted_offset = window_size - 1, so instead we must calculate: + * + * num_position_slots = 1 + lzx_get_position_slot_raw(window_size - 1); + * + * ... which is the same as + * + * num_position_slots = lzx_get_position_slot_raw(window_size); + * + * ... since every valid window size is equal to a position base value. + */ unsigned num_position_slots = lzx_get_position_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) + * combinations). */ return LZX_NUM_CHARS + (num_position_slots << 3); } + +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); +}