From 64b5917736396754a8f93c2913f5276361831b39 Mon Sep 17 00:00:00 2001 From: Chenxi Mao Date: Fri, 31 May 2019 08:36:13 +0800 Subject: [PATCH] FAST_DEC_LOOP: only did offset check in specific condition. When I did FAST_DEC_LOOP performance test, I found the offset check is much more than v1.8.3 You will see the condition check difference via lzbench with dickens test case. v1.8.3 34959 v.1.9.x 1055885 After investigate the code, we could see the difference. v.1.8.3 SKIP the condition check if if condition is true in: https://github.com/lz4/lz4/blob/v1.8.3/lib/lz4.c#L1463 AND below condition is true https://github.com/lz4/lz4/blob/v1.8.3/lib/lz4.c#L1478\ The offset check should be invoked. v1.9.3 The offset check code will be invoked in every loop which lead to downgrade. So the fix would be move this check to specific condition to avoid useless condition check. After this change, the call number is same as v1.8.3 --- lib/lz4.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/lib/lz4.c b/lib/lz4.c index 070dd7e..9e6999f 100644 --- a/lib/lz4.c +++ b/lib/lz4.c @@ -1708,10 +1708,9 @@ LZ4_decompress_generic( /* get matchlength */ length = token & ML_MASK; - if ((checkOffset) && (unlikely(match + dictSize < lowPrefix))) { goto _output_error; } /* Error : offset outside buffers */ - if (length == ML_MASK) { variable_length_error error = ok; + if ((checkOffset) && (unlikely(match + dictSize < lowPrefix))) { goto _output_error; } /* Error : offset outside buffers */ length += read_variable_length(&ip, iend - LASTLITERALS + 1, endOnInput, 0, &error); if (error != ok) { goto _output_error; } if ((safeDecode) && unlikely((uptrval)(op)+length<(uptrval)op)) { goto _output_error; } /* overflow detection */ @@ -1735,6 +1734,7 @@ LZ4_decompress_generic( continue; } } } + if ((checkOffset) && (unlikely(match + dictSize < lowPrefix))) { goto _output_error; } /* Error : offset outside buffers */ /* match starting within external dictionary */ if ((dict==usingExtDict) && (match < lowPrefix)) { if (unlikely(op+length > oend-LASTLITERALS)) { -- 2.7.4