pitrou commented on a change in pull request #9582:
URL: https://github.com/apache/arrow/pull/9582#discussion_r584709632
##########
File path: cpp/src/parquet/statistics.cc
##########
@@ -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;
+ }
+ // When the lengths are unequal and the numbers are of the same
+ // sign we need to extend the digits.
Review comment:
I'm not sure why all this is needed. The first bytes are equal.
Regardless of the sign, wouldn't it be sufficient to write e.g.:
```c++
return std::lexicographical_compare(a.ptr + 1, a.ptr + a_length, b.ptr +
1, b.ptr + b_length);
```
i.e. only the MSB in a two's complement integer needs special handling, the
other bytes are ordered naturally.
##########
File path: cpp/src/parquet/statistics.cc
##########
@@ -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:
Why can't use always short-circuit if the first bytes are unequal?
Intuitively:
```c++
if (first_a != first_b) {
return (first_a ^ 0x80) < (first_b ^ 0x80);
}
```
##########
File path: cpp/src/parquet/statistics_test.cc
##########
@@ -111,21 +117,28 @@ TEST(Comparison, UnsignedByteArray) {
}
TEST(Comparison, SignedFLBA) {
- int size = 10;
+ int size = 4;
auto comparator =
MakeComparator<FLBAType>(Type::FIXED_LEN_BYTE_ARRAY, SortOrder::SIGNED,
size);
- std::string s1 = "Anti123456";
- std::string s2 = "Bunkd123456";
- FLBA s1flba = FLBAFromString(s1);
- FLBA s2flba = FLBAFromString(s2);
- ASSERT_TRUE(comparator->Compare(s1flba, s2flba));
+ std::vector<uint8_t> byte_values[] = {
+ {0x80, 0, 0, 0}, {0xFF, 0xFF, 0x01, 0}, {0xFF, 0xFF, 0x80,
0},
+ {0xFF, 0xFF, 0xFF, 0x80}, {0xFF, 0xFF, 0xFF, 0xFF}, {0, 0, 0x01, 0x01},
+ {0, 0x01, 0x01, 0}, {0x01, 0x01, 0, 0}};
+ std::vector<FLBA> values_to_compare;
+ for (auto& bytes : byte_values) {
+ values_to_compare.emplace_back(FLBA(bytes.data()));
+ }
- s1 = "Bünk123456";
- s2 = "Bunk123456";
- s1flba = FLBAFromString(s1);
- s2flba = FLBAFromString(s2);
- ASSERT_TRUE(comparator->Compare(s1flba, s2flba));
+ for (size_t x = 0; x < values_to_compare.size(); x++) {
+ EXPECT_FALSE(comparator->Compare(values_to_compare[x],
values_to_compare[x])) << x;
+ for (size_t y = x + 1; y < values_to_compare.size(); y++) {
+ EXPECT_TRUE(comparator->Compare(values_to_compare[x],
values_to_compare[y]))
+ << x << " " << y;
+ EXPECT_FALSE(comparator->Compare(values_to_compare[y],
values_to_compare[x]))
+ << y << " " << x;
+ }
+ }
Review comment:
Do these tests cover the decimal case?
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