Function numeric_bucket_bits 

pub fn numeric_bucket_bits(n: Numeric) -> u64

The f64 a numeric reading rounds to, by the same conversion cmp_numeric uses for a decimal against a float. Two readings cmp_numeric orders Equal round to the same f64, with -0.0 read as 0.0 and every NaN as one NaN. Distinct readings can share an f64, so this is a hash bucket, never an equality.