xorWord

private fn

void xorWord(ulong  ab,  ulong  av,  ulong  bb,  ulong  bv,  size_t n,
       ref  ulong  rb,  ref  ulong  rv)

@safe pure nothrow

One xor word: null operands propagate, otherwise the value bits differ.

`ab`	the left value bits
`av`	the left validity bits
`bb`	the right value bits
`bv`	the right validity bits
`n`	the number of slots (the tail bits are ignored)
`rb`	the result value bits
`rv`	the result validity bits