const CANONICAL_NAN_BITS: u64 = 0x7FF8_0000_0000_0000;Expand description
Bits of the one NaN every NaN key is stored as: positive and quiet, so
f64::total_cmp orders it after +Inf on every platform (x86’s 0/0 has
the sign bit set), and its low word is not R’s NA payload (1954).