     The files in this directory support an increase in the precision
     of the functions in the 'xarm' library segment. This is accomplished
     by increasing the size of the mantissa. Possible enhanced mantissa
     sizes are 11, 15, 19, 23, 27, and 31 sixteen bit words. First
     redefine XDIM in 'xpre.h' to be equal to one of these values,
     then replace the 'constant.h' header with the corresponding
     'const[nn].h' from this directory, and recompile the segment code
     with these new header files.
