Copilot commented on code in PR #17208:
URL: https://github.com/apache/pinot/pull/17208#discussion_r2525736675
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pinot-common/src/main/java/org/apache/pinot/common/function/scalar/ArithmeticFunctions.java:
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@@ -201,6 +204,30 @@ public static double truncate(double a) {
return Math.signum(a) * Math.floor(Math.abs(a));
}
+ @ScalarFunction
+ public static double rand() {
+ return ThreadLocalRandom.current().nextDouble();
+ }
+
+ @ScalarFunction
+ public static double rand(long seed) {
+ return deterministicRand(seed);
+ }
+
+ private static double deterministicRand(long seed) {
+ // Mirror java.util.Random's initial LCG scramble by xor'ing with the
well-known multiplier before
+ // feeding the value into the non-linear mix64 routine, which actually
provides the randomness here.
+ // Reference:
https://docs.oracle.com/javase/8/docs/api/java/util/Random.html
+ long mixed = mix64(seed ^ 0x5DEECE66DL);
+ return (mixed >>> 11) * DOUBLE_UNIT;
+ }
Review Comment:
The comment mentions 'the randomness here' which is misleading since this is
a deterministic function. Consider rephrasing to 'provides good distribution
properties' or 'provides bit mixing' to avoid confusion.
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