pitrou commented on a change in pull request #9582:
URL: https://github.com/apache/arrow/pull/9582#discussion_r584992780
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File path: cpp/src/parquet/statistics.cc
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@@ -133,56 +136,95 @@ struct CompareHelper<Int96Type, is_signed> {
static T Max(int type_length, const T& a, const T& b) {
return Compare(0, a, b) ? b : a;
}
-}; // namespace parquet
-
-template <typename DType, bool is_signed>
-struct ByteLikeCompareHelperBase {
- using T = ByteArrayType::c_type;
- using PtrType = typename std::conditional<is_signed, int8_t, uint8_t>::type;
+};
- static T DefaultMin() { return {}; }
- static T DefaultMax() { return {}; }
- static T Coalesce(T val, T fallback) { return val; }
+template <typename T, bool is_signed>
+struct BinaryLikeComparer {};
- static inline bool Compare(int type_length, const T& a, const T& b) {
- const auto* aptr = reinterpret_cast<const PtrType*>(a.ptr);
- const auto* bptr = reinterpret_cast<const PtrType*>(b.ptr);
- return std::lexicographical_compare(aptr, aptr + a.len, bptr, bptr +
b.len);
+template <typename T>
+struct BinaryLikeComparer<T, /*is_signed=*/false> {
+ static bool Compare(int type_length, const T& a, const T& b) {
+ int a_length = value_length(type_length, a);
+ int b_length = value_length(type_length, b);
+ // Unsigned comparison is used for non-numeric types so straight
+ // lexiographic comparison makes sense. (a.ptr is always unsigned)....
+ return std::lexicographical_compare(a.ptr, a.ptr + a_length, b.ptr, b.ptr
+ b_length);
}
+};
- static T Min(int type_length, const T& a, const T& b) {
- if (a.ptr == nullptr) return b;
- if (b.ptr == nullptr) return a;
- return Compare(type_length, a, b) ? a : b;
- }
+template <typename T>
+struct BinaryLikeComparer<T, /*is_signed=*/true> {
+ static bool Compare(int type_length, const T& a, const T& b) {
+ // Is signed is used for integers encoded as big-endian twos
+ // complement integers. (e.g. decimals).
+ int a_length = value_length(type_length, a);
+ int b_length = value_length(type_length, b);
+
+ // At least of the lengths is zero.
+ if (a_length == 0 || b_length == 0) {
+ return a_length == 0 && b_length > 0;
+ }
- static T Max(int type_length, const T& a, const T& b) {
- if (a.ptr == nullptr) return b;
- if (b.ptr == nullptr) return a;
- return Compare(type_length, a, b) ? b : a;
+ int8_t first_a = *a.ptr;
+ int8_t first_b = *b.ptr;
+ // We can short circuit for different signed numbers or
+ // for equal length bytes arrays that have different first bytes.
+ if ((0x80 & first_a) != (0x80 & first_b) ||
+ (a_length == b_length && first_a != first_b)) {
+ return first_a < first_b;
+ }
Review comment:
Hmm, I see. I'll take a closer look :-)
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