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Add prefetch instructions in FindMatchLength #104

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Add prefetch instructions in FindMatchLength #104

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15 changes: 15 additions & 0 deletions snappy-internal.h
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Original file line number Diff line number Diff line change
Expand Up @@ -97,13 +97,28 @@ char* CompressFragment(const char* input,
// Separate implementation for 64-bit, little-endian cpus.
#if !defined(SNAPPY_IS_BIG_ENDIAN) && \
(defined(ARCH_K8) || defined(ARCH_PPC) || defined(ARCH_ARM))

#if ARCH_ARM
static inline void Prefetch(const void* data) {
__asm__ __volatile__(
"prfm PLDL1STRM, [%[data]] \n\t"
:: [data] "r" (data)
);
}
#endif //ARCH_ARM

static inline std::pair<size_t, bool> FindMatchLength(const char* s1,
const char* s2,
const char* s2_limit,
uint64_t* data) {
assert(s2_limit >= s2);
size_t matched = 0;

#if ARCH_ARM
Prefetch(s1 + 256);
Prefetch(s2 + 256);
#endif //ARCH_ARM

// This block isn't necessary for correctness; we could just start looping
// immediately. As an optimization though, it is useful. It creates some not
// uncommon code paths that determine, without extra effort, whether the match
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