parthchandra commented on code in PR #3939:
URL: https://github.com/apache/datafusion-comet/pull/3939#discussion_r3102903836
##########
native/spark-expr/src/conversion_funcs/numeric.rs:
##########
@@ -569,6 +573,62 @@ pub(crate) fn format_decimal_str(value_str: &str,
precision: usize, scale: i8) -
}
}
+/// Casts a Decimal128 array to string using Java's BigDecimal.toString()
semantics,
+/// which is Spark's LEGACY eval mode behavior. Plain notation when scale >= 0
and
+/// adjusted_exponent >= -6, otherwise scientific notation (e.g. "0E-18" for
zero
+/// with scale=18, since adjusted_exponent = -18 + 0 = -18 < -6).
+///
+/// TRY and ANSI modes produce plain notation via DataFusion's cast instead.
+pub(crate) fn cast_decimal128_to_utf8(array: &ArrayRef, scale: i8) ->
SparkResult<ArrayRef> {
+ let decimal_array = array
+ .as_any()
+ .downcast_ref::<Decimal128Array>()
+ .expect("Expected a Decimal128Array");
+ let output: StringArray = decimal_array
+ .iter()
+ .map(|opt_val| opt_val.map(|unscaled|
decimal128_to_java_string(unscaled, scale)))
+ .collect();
+ Ok(Arc::new(output))
+}
+
+/// Formats a Decimal128 unscaled value as a string matching Java's
BigDecimal.toString():
+/// - Plain notation when scale >= 0 and adjusted_exponent >= -6
+/// - Scientific notation otherwise
+///
+/// adjusted_exponent = -scale + (numDigits - 1)
+fn decimal128_to_java_string(unscaled: i128, scale: i8) -> String {
+ let negative = unscaled < 0;
+ let sign = if negative { "-" } else { "" };
+ let coeff = unscaled.unsigned_abs().to_string();
+ let num_digits = coeff.len() as i64;
+ let adj_exp = -(scale as i64) + (num_digits - 1);
+
+ if scale >= 0 && adj_exp >= -6 {
+ let scale_u = scale as usize;
+ let num_digits_u = num_digits as usize;
+ if scale_u == 0 {
+ format!("{sign}{coeff}")
Review Comment:
changed
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