andygrove commented on code in PR #19503:
URL: https://github.com/apache/datafusion/pull/19503#discussion_r2648636575
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datafusion/functions/src/string/to_hex.rs:
##########
@@ -37,32 +36,31 @@ use datafusion_expr::{ScalarFunctionArgs, ScalarUDFImpl,
Signature, Volatility};
use datafusion_expr_common::signature::TypeSignature::Exact;
use datafusion_macros::user_doc;
+/// Hex lookup table for fast conversion
+const HEX_CHARS: &[u8; 16] = b"0123456789abcdef";
+
/// Converts the number to its equivalent hexadecimal representation.
/// to_hex(2147483647) = '7fffffff'
fn to_hex<T: ArrowPrimitiveType>(args: &[ArrayRef]) -> Result<ArrayRef>
where
- T::Native: std::fmt::LowerHex,
+ T::Native: ToHex,
{
let integer_array = as_primitive_array::<T>(&args[0])?;
+ // Max hex string length: 16 chars for u64/i64
+ let max_hex_len = T::Native::get_byte_width() * 2;
let mut result = GenericStringBuilder::<i32>::with_capacity(
integer_array.len(),
- // * 8 to convert to bits, / 4 bits per hex char
- integer_array.len() * (T::Native::get_byte_width() * 8 / 4),
+ integer_array.len() * max_hex_len,
);
+ // Reusable buffer to avoid allocations - sized for max possible hex output
+ let mut buffer = [0u8; 16];
+
for integer in integer_array {
if let Some(value) = integer {
- if let Some(value_usize) = value.to_usize() {
- write!(result, "{value_usize:x}")?;
- } else if let Some(value_isize) = value.to_isize() {
- write!(result, "{value_isize:x}")?;
- } else {
- return exec_err!(
- "Unsupported data type {integer:?} for function to_hex"
- );
- }
- result.append_value("");
+ let hex_str = value.to_hex(&mut buffer);
Review Comment:
Thanks, it is even faster now! I updated the benchmark results in the PR
description.
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