liamzwbao commented on code in PR #8655:
URL: https://github.com/apache/arrow-rs/pull/8655#discussion_r2446238442
##########
parquet-variant-compute/src/type_conversion.rs:
##########
@@ -239,44 +247,22 @@ where
false if r <= half_neg => d.sub_wrapping(I::Native::ONE),
_ => d,
};
- O::Native::from_decimal(adjusted)
- };
- scaled.filter(|v| is_infallible_cast || O::is_valid_decimal_precision(*v,
output_precision))
-}
-
-/// Returns true if casting from (input_precision, input_scale) to
-/// (output_precision, output_scale) is infallible based on precision/scale
math.
-fn is_infallible_decimal_cast(
- input_precision: u8,
- input_scale: i8,
- output_precision: u8,
- output_scale: i8,
-) -> bool {
- let delta_scale = output_scale - input_scale;
- let input_precision = input_precision as i8;
- let output_precision = output_precision as i8;
- if delta_scale >= 0 {
- // if the gain in precision (digits) is greater than the
multiplication due to scaling
- // every number will fit into the output type
- // Example: If we are starting with any number of precision 5 [xxxxx],
- // then an increase of scale by 3 will have the following effect on
the representation:
- // [xxxxx] -> [xxxxx000], so for the cast to be infallible, the output
type
- // needs to provide at least 8 digits precision
- input_precision + delta_scale <= output_precision
- } else {
// if the reduction of the input number through scaling (dividing) is
greater
// than a possible precision loss (plus potential increase via
rounding)
// every input number will fit into the output type
// Example: If we are starting with any number of precision 5 [xxxxx],
// then and decrease the scale by 3 will have the following effect on
the representation:
// [xxxxx] -> [xx] (+ 1 possibly, due to rounding).
- // The rounding may add an additional digit, so for the cast to be
infallible,
+ // The rounding may add a digit, so for the cast to be infallible,
// the output type needs to have at least 3 digits of precision.
// e.g. Decimal(5, 3) 99.999 to Decimal(3, 0) will result in 100:
// [99999] -> [99] + 1 = [100], a cast to Decimal(2, 0) would not be
possible
- input_precision + delta_scale < output_precision
- }
+ let is_infallible_cast = input_precision as i8 + delta_scale <
output_precision as i8;
+ (O::Native::from_decimal(adjusted), is_infallible_cast)
+ };
+
+ scaled.filter(|v| is_infallible_cast || O::is_valid_decimal_precision(*v,
output_precision))
Review Comment:
To make it simple, how about this
```rs
if is_infallible_cast {
scaled
} else {
scaled.filter(|v| O::is_valid_decimal_precision(*v,
output_precision))
}
```
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