comphead commented on code in PR #19568:
URL: https://github.com/apache/datafusion/pull/19568#discussion_r2653906392
##########
datafusion/functions/src/crypto/basic.rs:
##########
@@ -157,14 +157,18 @@ pub fn md5(args: &[ColumnarValue]) ->
Result<ColumnarValue> {
})
}
-/// this function exists so that we do not need to pull in the crate hex. it
is only used by md5
-/// function below
+/// Hex encoding lookup table for fast byte-to-hex conversion
+const HEX_CHARS_LOWER: &[u8; 16] = b"0123456789abcdef";
+
+/// Fast hex encoding using a lookup table instead of format strings.
+/// This is significantly faster than using `write!("{:02x}")` for each byte.
#[inline]
fn hex_encode<T: AsRef<[u8]>>(data: T) -> String {
Review Comment:
great, curious if that would be more performance if create a string directly
from bytes without utf checks(which is redundant ) and extract casts?
```
let bytes = data.as_ref();
let mut out = Vec::with_capacity(bytes.len() * 2);
for &b in bytes {
out.push(HEX_CHARS_LOWER[(b >> 4) as usize]);
out.push(HEX_CHARS_LOWER[(b & 0x0f) as usize]);
}
unsafe { String::from_utf8_unchecked(out) }
```
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