feat(expression): cast numeric literals to decimal type#805
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Pull request overview
This PR extends Literal::CastTo to support casting numeric literals (int, long, float, double) into a decimal target type, aligning C++ literal-cast behavior with Java’s numeric-to-decimal default handling. It adds new decimal-cast logic for integer and real sources and introduces targeted unit tests to validate scaling, rounding, and rejection behavior.
Changes:
- Add integer→decimal and real→decimal cast paths in
LiteralCaster, including HALF_UP rounding behavior. - Add
RescaleHalfUphelper to support HALF_UP rounding (including negative target scales) while avoiding unsafe power-of-ten indexing in some cases. - Add new tests covering integer/real decimal casts, scale handling, rounding behavior, and error cases.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.
| File | Description |
|---|---|
| src/iceberg/expression/literal.cc | Adds numeric→decimal casting logic and a HALF_UP rescaling helper used by Literal::CastTo. |
| src/iceberg/test/literal_test.cc | Adds unit tests validating integer/real casts to decimal, rounding rules, and error handling. |
Validate target scale bounds, avoid int128 overflow in HALF_UP by comparing against divisor/2, and use std::to_chars for shortest round-trip conversion.
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What
Add casting of numeric literals (
int,long,float,double) to a decimal target type inLiteral::CastTo, so a numeric value can be used as a default for a decimal column.Previously
CastFromInt/CastFromLong/CastFromFloat/CastFromDoublehad nokDecimalcase and fell through toNotSupported, so a default likeLiteral::Int(12)orLiteral::Double(9.99)for adecimal(9, 2)column was rejected. Java allows these (IntegerLiteral.to,DoubleLiteral.to, etc. scale the value to the target scale), so this brings the C++ literal cast layer to parity for numeric sources.How
CastIntegerToDecimalscales the integer (scale 0) up to the target scale viaDecimal::Rescale(0, scale), then verifies the result fits the target precision (FitsInPrecision). Example:12→decimal(9,2)yields unscaled1200(12.00).CastRealToDecimalparses the value's shortest round-tripping decimal representation (matching Java'sBigDecimal.valueOf(double)viaDouble.toString), then rounds to the target scale with HALF_UP rounding (round half away from zero, as Java does —2.5→3,-2.5→-3), and checks precision. Non-finite values are rejected.DecimalTypedoes not bound its scale on construction, sodecimal(9, 40)would otherwise read past the table).Scope
Follow-up split out from the v3 default-value work (see the
CastDefaultToTypediscussion on #793). It only extends the sharedLiteral::CastTolayer for numeric sources.Testing
LiteralTest.IntegerCastToDecimal(int/long scaling, out-of-precision rejection, out-of-range scale rejection) andLiteralTest.RealCastToDecimal(float/double scaling, HALF_UP rounding incl. negative, round-down, out-of-precision and non-finite rejection), all verified fail-without / pass-with. Fullexpression_testpasses (495 tests).