comphead commented on code in PR #20116:
URL: https://github.com/apache/datafusion/pull/20116#discussion_r2756873186
##########
datafusion/spark/src/function/hash/sha2.rs:
##########
@@ -144,11 +205,16 @@ where
Arc::new(array)
}
+const HEX_CHARS: [u8; 16] = *b"0123456789abcdef";
+
+#[inline]
fn hex_encode<T: AsRef<[u8]>>(data: T) -> String {
- let mut s = String::with_capacity(data.as_ref().len() * 2);
- for b in data.as_ref() {
- // Writing to a string never errors, so we can unwrap here.
- write!(&mut s, "{b:02x}").unwrap();
+ let bytes = data.as_ref();
+ let mut out = Vec::with_capacity(bytes.len() * 2);
+ for &b in bytes {
+ out.push(HEX_CHARS[(b >> 4) as usize]);
Review Comment:
it might be a reason for extra boundaries check, maybe worth to check also
```
let hi = b >> 4;
let lo = b & 0x0F;
out.push(HEX_CHARS[hi as usize]);
out.push(HEX_CHARS[lo as usize]);
```
rustc might be smart enough to rewrite by itself
##########
datafusion/spark/src/function/hash/sha2.rs:
##########
@@ -144,11 +205,16 @@ where
Arc::new(array)
}
+const HEX_CHARS: [u8; 16] = *b"0123456789abcdef";
+
+#[inline]
fn hex_encode<T: AsRef<[u8]>>(data: T) -> String {
- let mut s = String::with_capacity(data.as_ref().len() * 2);
- for b in data.as_ref() {
- // Writing to a string never errors, so we can unwrap here.
- write!(&mut s, "{b:02x}").unwrap();
+ let bytes = data.as_ref();
+ let mut out = Vec::with_capacity(bytes.len() * 2);
+ for &b in bytes {
+ out.push(HEX_CHARS[(b >> 4) as usize]);
Review Comment:
it might be a reason for extra LLVM boundaries check, maybe worth to check
also
```
let hi = b >> 4;
let lo = b & 0x0F;
out.push(HEX_CHARS[hi as usize]);
out.push(HEX_CHARS[lo as usize]);
```
rustc might be smart enough to rewrite by itself
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