wgtmac commented on code in PR #805:
URL: https://github.com/apache/iceberg-cpp/pull/805#discussion_r3563434385
##########
src/iceberg/expression/literal.cc:
##########
@@ -95,6 +104,71 @@ Literal
LiteralCaster::AboveMaxLiteral(std::shared_ptr<PrimitiveType> type) {
return Literal(Literal::AboveMax{}, std::move(type));
}
+Result<Literal> LiteralCaster::CastIntegerToDecimal(
+ int64_t value, const std::shared_ptr<PrimitiveType>& target_type) {
+ const auto& decimal_type = internal::checked_cast<const
DecimalType&>(*target_type);
+ const int32_t scale = decimal_type.scale();
+ // DecimalType does not bound its scale, but Rescale indexes a powers-of-ten
table sized
+ // for [0, kMaxScale]; reject an out-of-range scale here rather than reading
past it.
+ if (scale < 0 || scale > Decimal::kMaxScale) {
+ return InvalidArgument("Cannot cast {} as a {} value", value,
+ target_type->ToString());
+ }
+ // An integer has scale 0, so scaling it to the target scale multiplies the
unscaled
+ // value by 10^scale; Rescale rejects a target scale that would overflow the
value.
+ ICEBERG_ASSIGN_OR_RAISE(auto decimal, Decimal(value).Rescale(0, scale));
+ if (!decimal.FitsInPrecision(decimal_type.precision())) {
+ return InvalidArgument("Cannot cast {} as a {} value", value,
+ target_type->ToString());
+ }
+ return Literal::Decimal(decimal.value(), decimal_type.precision(),
+ decimal_type.scale());
+}
+
+Result<Literal> LiteralCaster::CastRealToDecimal(
+ double value, const std::shared_ptr<PrimitiveType>& target_type) {
+ const auto& decimal_type = internal::checked_cast<const
DecimalType&>(*target_type);
+ const int32_t target_scale = decimal_type.scale();
+ if (target_scale < 0 || target_scale > Decimal::kMaxScale) {
+ return InvalidArgument("Cannot cast {} as a {} value", value,
+ target_type->ToString());
+ }
+ if (!std::isfinite(value)) {
+ return InvalidArgument("Cannot cast {} as a {} value", value,
+ target_type->ToString());
+ }
+
+ // Parse the shortest round-tripping decimal representation of the value
(matching
+ // Java's BigDecimal.valueOf(double), which goes through Double.toString)
into a
+ // full-precision decimal, then round to the target scale below.
+ int32_t parsed_scale = 0;
+ ICEBERG_ASSIGN_OR_RAISE(
+ auto parsed, Decimal::FromString(std::format("{}", value), nullptr,
&parsed_scale));
+
+ Decimal unscaled = parsed;
+ if (parsed_scale > target_scale) {
+ // Drop excess fractional digits with HALF_UP rounding (round half away
from zero, as
+ // Java does), since Rescale itself only truncates and rejects any dropped
remainder.
+ const int32_t drop = parsed_scale - target_scale;
+ ICEBERG_ASSIGN_OR_RAISE(auto divisor, Decimal(1).Rescale(0, drop));
Review Comment:
Please guard `drop` before calling `Rescale`. For values like `1e-100` cast
to `decimal(9,2)`, `drop` is 98 and indexes past the powers-of-ten table; Java
rounds this to `0.00`.
##########
src/iceberg/expression/literal.cc:
##########
@@ -95,6 +104,71 @@ Literal
LiteralCaster::AboveMaxLiteral(std::shared_ptr<PrimitiveType> type) {
return Literal(Literal::AboveMax{}, std::move(type));
}
+Result<Literal> LiteralCaster::CastIntegerToDecimal(
+ int64_t value, const std::shared_ptr<PrimitiveType>& target_type) {
+ const auto& decimal_type = internal::checked_cast<const
DecimalType&>(*target_type);
+ const int32_t scale = decimal_type.scale();
+ // DecimalType does not bound its scale, but Rescale indexes a powers-of-ten
table sized
+ // for [0, kMaxScale]; reject an out-of-range scale here rather than reading
past it.
+ if (scale < 0 || scale > Decimal::kMaxScale) {
Review Comment:
Please allow negative decimal scales here and in the real-value path.
Iceberg decimal(P,S) supports negative S, and Java uses `setScale(scale,
HALF_UP)`, so `149 -> decimal(9,-2)` should round to `1E+2` instead of failing.
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