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Replace the division with a constant table in IncrementalCopy

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PiperOrigin-RevId: 320686580
This commit is contained in:
Snappy Team
2020-07-10 22:21:23 +00:00
committed by Victor Costan
parent f16eda3466
commit 4dd277fed4
1 changed files with 4 additions and 1 deletions
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snappy.cc
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@@ -177,6 +177,9 @@ alignas(16) const char pshufb_fill_patterns[7][16] = {
{0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 0, 1},
};
// j * (16 / j) for all j from 0 to 7. 0 is not actually used.
const uint8_t pattern_size_table[8] = {0, 16, 16, 15, 16, 15, 12, 14};
#endif // SNAPPY_HAVE_SSSE3
// Copy [src, src+(op_limit-op)) to [op, (op_limit-op)) but faster than
@@ -248,7 +251,7 @@ inline char* IncrementalCopy(const char* src, char* op, char* const op_limit,
// Uninitialized bytes are masked out by the shuffle mask.
// TODO: remove annotation and macro defs once MSan is fixed.
SNAPPY_ANNOTATE_MEMORY_IS_INITIALIZED(&pattern, sizeof(pattern));
pattern_size *= 16 / pattern_size;
pattern_size = pattern_size_table[pattern_size];
char* op_end = std::min(op_limit, buf_limit - 15);
while (op < op_end) {
_mm_storeu_si128(reinterpret_cast<__m128i*>(op), pattern);