Splits nodes in a tree bin into lower and upper tree bins,
or untreeifies if now too small. Called only from resize;
see above discussion about split bits and indices.
@param map the map
@param tab the table for recording bin heads
@param index the index of the table being split
@param bit the bit of hash to split on
Splits nodes in a tree bin into lower and upper tree bins, or untreeifies if now too small. Called only from resize; see above discussion about split bits and indices.
@param map the map @param tab the table for recording bin heads @param index the index of the table being split @param bit the bit of hash to split on