pitrou commented on code in PR #50483:
URL: https://github.com/apache/arrow/pull/50483#discussion_r3630157897
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cpp/src/arrow/csv/lexing_internal.h:
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@@ -138,6 +144,13 @@ class SSE42Filter {
_SIDD_UBYTE_OPS | _SIDD_CMP_EQUAL_ANY);
}
+ // _mm_cmpistrc is an implicit-length compare: it treats a NUL byte as a
+ // terminator and can miss a real delimiter/quote/newline sharing an 8-byte
+ // word with one. Never use this filter on a block that contains a NUL.
Review Comment:
Let's explain why we don't use the explicit-length compare instruction
```suggestion
// _mm_cmpistrc is an implicit-length compare: it treats a NUL byte as a
// terminator and can miss a real delimiter/quote/newline sharing an 8-byte
// word with one. Never use this filter on a block that contains a NUL.
// We could instead use the explicit-length compare _mm_cmpestrc but
// it comes with a massive performance cost on some CPUs
// (some benchmarks were measured to be twice slower in
// https://github.com/apache/arrow/pull/50483).
```
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