qtod copies its standard input to standard output, converting Fortran quadruple-precision constants, built-in functions, and type declarations to double precision.
Floating-point FORMAT specifications are left intact; on some ancient systems, they may require modifications. They do not under the rules of Fortran 77.
Leading tabs are correctly interpreted according to common extended Fortran rules.
qtod recognizes all of the standard Fortran 77 double-precision functions, quadruple-precision extensions, the pair qrand/drand (UNIX pseudo-random number generators), and the pair q1mach/d1mach from the PORT library framework.
Although quadruple precision is not provided for by the Fortran 77 Standard, a number of vendors, including DEC, IBM, and Sun support it with data types REAL*16 and COMPLEX*32, together with a set of functions analogous to the double-precision Fortran functions, with the letter D in their names changed to Q. Quadruple-precision constants use the letter Q instead of D or E. Q format items already mean something else in some of these extended Fortrans, so D or E must be used instead.
qtod's other purpose is to demonstrate a modest lex(1) program.
Text beyond column 72 is discarded when lines are collected into Fortran statements.
qtod does not handle embedded ASCII tab characters correctly when long lines are to be broken. A Fortran-sensitive detabbing utility should be applied first if the input file possibly contains embedded tabs. Note that expand(1) cannot be used to do this job correctly!
Mixed-precision code may not be converted correctly. For example, QEXT(DFLOAT(N)) will become DBLE(DFLOAT(N)), which is syntactically incorrect.
Functions and variables of type COMPLEX are not converted, because Fortran 77 does not define a quadruple precision complex type. Complex constants will be converted, however, since their real and imaginary parts look like normal floating-point values.