diff options
author | costan <costan@google.com> | 2017-08-23 20:59:46 -0700 |
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committer | Victor Costan <pwnall@chromium.org> | 2017-08-24 15:00:52 -0700 |
commit | 2964b803b857932ff7499d7bebb61dc5514dab7c (patch) | |
tree | 0d5bebb45495feef0a5f48af286ea82b0d28eb32 | |
parent | 02f43c0fcde39823830493503e8a3f72fed43d24 (diff) | |
download | leveldb-2964b803b857932ff7499d7bebb61dc5514dab7c.tar.gz |
leveldb: Fix alignment code in SSE4.2-optimized CRC32C.
When faced with a pointer that is misaligned by K bytes (pointer % 8 ==
K), the code previously moved forward by K bytes. In order to end up
with an aligned pointer, the code must move by 8 - K bytes.
This lands https://github.com/google/leveldb/pull/488
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=166295921
-rw-r--r-- | port/port_posix_sse.cc | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/port/port_posix_sse.cc b/port/port_posix_sse.cc index 1e519ba..08d9aee 100644 --- a/port/port_posix_sse.cc +++ b/port/port_posix_sse.cc @@ -92,8 +92,12 @@ uint32_t AcceleratedCRC32C(uint32_t crc, const char* buf, size_t size) { } while (0) if (size > 16) { - // Process unaligned bytes - for (unsigned int i = reinterpret_cast<uintptr_t>(p) % 8; i; --i) { + // Point x at first 8-byte aligned byte in string. This must be inside the + // string, due to the size check above. + const uintptr_t pval = reinterpret_cast<uintptr_t>(p); + const uint8_t* x = reinterpret_cast<const uint8_t*>(((pval + 7) >> 3) << 3); + // Process bytes until p is 8-byte aligned. + while (p != x) { STEP1; } |