pitrou commented on code in PR #53327:
URL: https://github.com/apache/arrow/pull/53327#discussion_r4440388785
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cpp/src/arrow/compute/kernels/scalar_cast_test.cc:
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@@ -1726,6 +1726,45 @@ TEST(Cast, Decimal128ToDecimal32) {
}
}
+// GH-53288: narrowing to Decimal32 must rescale and range-check the full-width
Review Comment:
Please augment Decimal128ToDecimal32 instead
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cpp/src/arrow/compute/kernels/scalar_cast_numeric.cc:
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@@ -486,8 +486,12 @@ struct DecimalConversions<Decimal256, InDecimal> {
template <typename InDecimal>
struct DecimalConversions<Decimal32, InDecimal> {
- static Decimal32 ConvertInput(InDecimal&& val) { return
Decimal32(val.low_bits()); }
- static Decimal32 ConvertOutput(Decimal32&& val) { return val; }
+ // Scale then truncate. Narrowing in ConvertInput would drop coefficient bits
+ // before Rescale and FitsInPrecision could see them.
Review Comment:
No need to expand on this.
```suggestion
// Scale then truncate.
```
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