wgtmac commented on code in PR #48717:
URL: https://github.com/apache/arrow/pull/48717#discussion_r2665550214
##########
cpp/src/parquet/statistics.cc:
##########
@@ -290,7 +296,26 @@ struct BinaryLikeCompareHelperBase {
template <bool is_signed>
struct CompareHelper<ByteArrayType, is_signed>
- : public BinaryLikeCompareHelperBase<ByteArrayType, is_signed> {};
+ : public BinaryLikeCompareHelperBase<ByteArrayType, is_signed> {
+ using Base = BinaryLikeCompareHelperBase<ByteArrayType, is_signed>;
+ using T = ByteArray;
+
+ // Use kNoValueSentinel instead of nullptr to distinguish "no value" from
empty string.
+ static T DefaultMin() { return T{0, kNoValueSentinel}; }
+ static T DefaultMax() { return T{0, kNoValueSentinel}; }
+
+ static T Min(int type_length, const T& a, const T& b) {
+ if (a.ptr == kNoValueSentinel) return b;
Review Comment:
Not related to this PR. Since it allows `ptr` to be nullptr for empty
string, following `Copy` may be a UB if min is an empty string with nullptr.
```cpp
template <>
inline void TypedStatisticsImpl<ByteArrayType>::Copy(const ByteArray& src,
ByteArray* dst,
ResizableBuffer*
buffer) {
if (dst->ptr == src.ptr) return;
PARQUET_THROW_NOT_OK(buffer->Resize(src.len, false));
std::memcpy(buffer->mutable_data(), src.ptr, src.len);
*dst = ByteArray(src.len, buffer->data());
}
```
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