Fortran 77 code is supposed to be also legal Fortran 95/03/08 code, so you could have just changed all the 32bit REAL's in the F77 code to real(dp) or something

Fortran 77 code is supposed to be also legal Fortran 95/03/08 code, so you could have just changed all the 32bit REAL's in the F77 code to real(dp) or something. But maybe recompiling the Fortran library you used would have been tricky for you.