bhanreddy1973 opened a new pull request, #19585:
URL: https://github.com/apache/datafusion/pull/19585
## Which issue does this PR close?
Closes #15986
## Rationale for this change
The current `hex` function implementation uses `write!(&mut s, "{b:02x}")`
for each byte, which has significant overhead from format string parsing.
## What changes are included in this PR?
Replaced the slow format-based hex encoding with pre-computed lookup tables
(HEX_UPPER/HEX_LOWER). Each byte value maps directly to its two-character hex
representation via simple array indexing.
Benefits:
- Eliminates format string parsing overhead
- Uses a single pre-sized allocation
- Simple array indexing instead of function calls per byte
## How are these changes tested?
All existing tests pass:
- test_hex_int64
- test_spark_hex_int64
- test_dictionary_hex_utf8
- test_dictionary_hex_int64
- test_dictionary_hex_binary
## Are these changes safe?
Yes - the lookup tables contain only valid ASCII hex characters, so the
conversion is safe. The behavior is identical to before, just faster.
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