Copilot commented on code in PR #60650:
URL: https://github.com/apache/doris/pull/60650#discussion_r2787110781
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be/src/util/hash_util.hpp:
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@@ -44,10 +45,78 @@ class HashUtil {
return (uint32_t)crc32(hash, (const unsigned char*)data, bytes);
}
+ // Inline CRC32 (zlib-compatible, standard CRC32 polynomial) for
fixed-size types.
+ // Uses Slicing-by-4 technique for 4/8-byte types: processes 4 bytes at a
time using
+ // 4 precomputed lookup tables, reducing serial table lookups from 4 to 1
per 4-byte chunk.
+ // Polynomial: 0xEDB88320 (reflected form of 0x04C11DB7).
+ // Endian note: CRC32 reflected algorithm processes bytes in address order
(byte[0] first).
+ // Slicing-by-4 requires byte[0] at LSB of the loaded uint32_t, which is
little-endian layout.
+ // LittleEndian::Load32 provides this on ALL platforms: noop on LE, bswap
on BE.
+ template <typename T>
+ static uint32_t zlib_crc32_fixed(const T& value, uint32_t hash) {
+ // Slicing-by-4 table: t[0] is the standard byte-at-a-time table,
+ // t[1..3] are extended tables for parallel 4-byte processing.
+ struct CRC32SliceBy4Table {
+ uint32_t t[4][256] {};
Review Comment:
`zlib_crc32_fixed` is a function template and defines `static constexpr
CRC32SliceBy4Table tbl` inside the template. This will instantiate (and
potentially emit) a separate 4x256 CRC table for every distinct `T` used across
the codebase, increasing compile time and binary size. Consider moving the
slice-by-4 table to a non-templated shared singleton (e.g., an
`inline`/`constinit` static in `HashUtil`, or a file-scope table) and have the
template reuse it.
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