arith: provides for simple integer arithmetic during the preprocessing of
code. arith: can be used to add, subtract, multiply, divide, and take powers of
two numerical arguments.
arith:(integer1,operator,integer2)
integer1 any digit string
operator the symbols + - * / **
integer2 any digit string
arith:(5,*,7) is replaced in the Fortran output by 35.
arith:(maxbits:,/,nbyte:) is replaced first by the values
of the macros maxbits: and nbyte: (say 60 and 6) and then
by the value 10.
