diff options
| -rw-r--r-- | Documentation/lzo.txt | 8 | ||||
| -rw-r--r-- | lib/lzo/lzo1x_compress.c | 13 |
2 files changed, 19 insertions, 2 deletions
diff --git a/Documentation/lzo.txt b/Documentation/lzo.txt index ca983328976b..f65b51523014 100644 --- a/Documentation/lzo.txt +++ b/Documentation/lzo.txt @@ -159,11 +159,15 @@ Byte sequences distance = 16384 + (H << 14) + D state = S (copy S literals after this block) End of stream is reached if distance == 16384 + In version 1 only, to prevent ambiguity with the RLE case when + ((distance & 0x803f) == 0x803f) && (261 <= length <= 264), the + compressor must not emit block copies where distance and length + meet these conditions. In version 1 only, this instruction is also used to encode a run of - zeros if distance = 0xbfff, i.e. H = 1 and the D bits are all 1. + zeros if distance = 0xbfff, i.e. H = 1 and the D bits are all 1. In this case, it is followed by a fourth byte, X. - run length = ((X << 3) | (0 0 0 0 0 L L L)) + 4. + run length = ((X << 3) | (0 0 0 0 0 L L L)) + 4 0 0 1 L L L L L (32..63) Copy of small block within 16kB distance (preferably less than 34B) diff --git a/lib/lzo/lzo1x_compress.c b/lib/lzo/lzo1x_compress.c index 717c940112f9..8ad5ba2b86e2 100644 --- a/lib/lzo/lzo1x_compress.c +++ b/lib/lzo/lzo1x_compress.c @@ -268,6 +268,19 @@ m_len_done: *op++ = (M4_MARKER | ((m_off >> 11) & 8) | (m_len - 2)); else { + if (unlikely(((m_off & 0x403f) == 0x403f) + && (m_len >= 261) + && (m_len <= 264)) + && likely(bitstream_version)) { + // Under lzo-rle, block copies + // for 261 <= length <= 264 and + // (distance & 0x80f3) == 0x80f3 + // can result in ambiguous + // output. Adjust length + // to 260 to prevent ambiguity. + ip -= m_len - 260; + m_len = 260; + } m_len -= M4_MAX_LEN; *op++ = (M4_MARKER | ((m_off >> 11) & 8)); while (unlikely(m_len > 255)) { |