morrySnow commented on code in PR #68029:
URL: https://github.com/apache/doris/pull/68029#discussion_r4058963674
##########
fe/fe-core/src/main/java/org/apache/doris/nereids/trees/expressions/functions/executable/NumericArithmetic.java:
##########
@@ -755,6 +756,45 @@ public static Expression factorial(BigIntLiteral first) {
return new BigIntLiteral(ArithmeticUtils.factorial((int) value));
}
+ /**
+ * gamma
+ *
+ * <p>The BE computes this with std::tgamma and maps the poles to NULL, so
this
+ * evaluation reproduces that outcome rather than the raw library
behaviour:
+ * commons-math3 returns NaN for everything that is not finite, while
std::tgamma
+ * returns an infinity at zero, at a large enough argument and at positive
infinity.
+ *
+ * <p>-Infinity is the one input where the two classifications differ in a
way that
+ * matters: the BE sees it as a negative integer, hence a pole, and yields
NULL.
+ *
+ * <p>Positive and negative inputs need different routes through
commons-math3.
+ * Gamma.gamma saturates to an infinity well before std::tgamma does - it
already
+ * overflows at 165, while std::tgamma still returns a finite 3.29e293
there - so
+ * positive inputs go through exp(logGamma(x)), which stays finite across
the range and
+ * agrees with std::tgamma to the last place. logGamma is not defined for
negative
+ * inputs, but that half has no overflow problem, so Gamma.gamma is used
there.
+ */
+ @ExecFunction(name = "gamma")
+ public static Expression gamma(DoubleLiteral first) {
+ double x = first.getValue();
+ if (Double.isNaN(x)) {
+ return new DoubleLiteral(Double.NaN);
+ }
+ if (Double.isInfinite(x)) {
+ // +inf overflows to itself; -inf is treated as a negative
integer, i.e. a pole.
+ return x > 0 ? new DoubleLiteral(Double.POSITIVE_INFINITY)
Review Comment:
If this function does not contribute to partition pruning and bucket
pruning, and cannot simply align the implementations of fe and be, then not
implementing the version of fe might be a better choice.
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