WillAyd commented on code in PR #1288:
URL: https://github.com/apache/arrow-adbc/pull/1288#discussion_r1391650537
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c/driver/postgresql/postgres_copy_reader.h:
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@@ -1217,6 +1217,77 @@ class PostgresCopyIntervalFieldWriter : public
PostgresCopyFieldWriter {
}
};
+
+// Inspiration for this taken from get_str_from_var in the pg source
+// src/backend/utils/adt/numeric.c
+class PostgresCopyNumericFieldWriter : public PostgresCopyFieldWriter {
+public:
+ ArrowErrorCode Write(ArrowBuffer* buffer, int64_t index, ArrowError* error)
override {
+ struct ArrowDecimal decimal;
+ // TODO: these need to be inferred from the schema not hard coded
+ constexpr int16_t precision = 19;
+ constexpr int16_t scale = 8;
+ ArrowDecimalInit(&decimal, 128, precision, scale);
+ ArrowArrayViewGetDecimalUnsafe(array_view_, index, &decimal);
+ constexpr uint16_t kNumericPos = 0x0000;
+ constexpr uint16_t kNumericNeg = 0x4000;
+ constexpr int64_t kNBase = 10000;
+ // Number of decimal digits per Postgres digit
+ constexpr int kDecDigits = 4;
+
+ // TODO: need some kind of bounds check on this
+ int64_t decimal_int = ArrowDecimalGetIntUnsafe(&decimal);
+ // TODO: is -INT64_MIN possible? If so how do we handle?
+ if (decimal_int < 0) {
+ decimal_int = -decimal_int;
+ }
+ std::vector<int16_t> pg_digits;
Review Comment:
Yea that's true and actually how postgres does it internally.
https://github.com/postgres/postgres/blob/8680bae8463a0b213893ca6a1c5bb2c2530e823c/src/backend/utils/adt/numeric.c#L8026
If we wanted to stack allocate I guess would just expand that out to
whatever is required to store up to 4 decimal words?
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