[tor-commits] [tor/master] csiphash: don't attempt unaligned access

[nickm@xxxxxxxxxxxxxx]

commit aaa33f144c4ad0db0c067df2f6703790be400acb
Author: Nick Mathewson <nickm@xxxxxxxxxxxxxx>
Date:   Tue Mar 18 10:43:46 2014 -0400

    csiphash: don't attempt unaligned access
    
    In digestmap_set/get benchmarks, doing unaligned access on x86
    doesn't save more than a percent or so in the fast case.  In the
    slow case (where we cross a cache line), it could be pretty
    expensive.  It also makes ubsan unhappy.
---
 src/ext/csiphash.c |    5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/ext/csiphash.c b/src/ext/csiphash.c
index 4f58c4a..2a96f28 100644
--- a/src/ext/csiphash.c
+++ b/src/ext/csiphash.c
@@ -81,11 +81,16 @@
 	HALF_ROUND(v0,v1,v2,v3,13,16);		\
 	HALF_ROUND(v2,v1,v0,v3,17,21);
 
+#if 0
+/* This does not seem to save very much runtime in the fast case, and it's
+ * potentially a big loss in the slow case where we're misaligned and we cross
+ * a cache line. */
 #if (defined(__i386) || defined(__i386__) || defined(_M_IX86) ||	\
      defined(__x86_64) || defined(__x86_64__) ||			\
      defined(_M_AMD64) || defined(_M_X64) || defined(__INTEL__))
 #   define UNALIGNED_OK 1
 #endif
+#endif
 
 uint64_t siphash24(const void *src, unsigned long src_sz, const struct sipkey *key) {
 	uint64_t k0 = key->k0;



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