Improve branch misses on FSE symbol spreading #2750
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Cyan4973
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Aug 18, 2021
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Some minor conversion warnings to take care off, |
senhuang42
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Cyan4973
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Aug 30, 2021
| int const n = normalizedCounter[s]; | ||
| MEM_write64(spread + pos, sv); | ||
| for (i = 8; i < n; i += 8) { | ||
| MEM_write64(spread + pos + i, sv); |
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Have we some form of guarantee that this won't overwrite beyond spread ?
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This can over-write up to 8 bytes beyond spread. So we need to make sure we have 1 << tableLog + 8 bytes available.
terrelln
reviewed
Aug 30, 2021
| int const n = normalizedCounter[s]; | ||
| MEM_write64(spread + pos, sv); | ||
| for (i = 8; i < n; i += 8) { | ||
| MEM_write64(spread + pos + i, sv); |
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This can over-write up to 8 bytes beyond spread. So we need to make sure we have 1 << tableLog + 8 bytes available.
| FSE_FUNCTION_TYPE* tableSymbol = (FSE_FUNCTION_TYPE*)(cumul + (maxSymbolValue + 2)); | ||
| U16* cumul = (U16*)workSpace; /* size = maxSV1 */ | ||
| FSE_FUNCTION_TYPE* tableSymbol = (FSE_FUNCTION_TYPE*)(cumul + (maxSV1+1)); /* size = tableSize */ | ||
| BYTE* spread = tableSymbol + tableSize; /* size = tableSize */ |
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The size should be tableSize + 8.
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This PR simply adds the same optimization as @terrelln's small block FSE decoding which reduces branch misses.