XL Fortran Enterprise Edition for AIX : User's Guide - IBM

-qdpc Option
Syntax
-qdpc[=e] | -qnodpc
DPC[(E)] | NODPC
Increases the precision of real constants, for maximum accuracy when assigning
real constants to DOUBLE PRECISION variables. This language extension might
be needed when you are porting programs from other platforms.
Rules
If you specify -qdpc, all basic real constants (for example, 1.1) are treated as
double-precision constants; the compiler preserves some digits of precision that
would otherwise be lost during the assignment to the DOUBLE PRECISION
variable. If you specify -qdpc=e, all single-precision constants, including constants
with an e exponent, are treated as double-precision constants.
This option does not affect constants with a kind type parameter specified.
Examples
@process nodpc
subroutine nodpc
real x
double precision y
data x /1.000000000001/
data y /1.000000000001/
print *, x, y, x .eq. y
end
@process dpc
subroutine dpc
real x
double precision y
data x /1.000000000001/
data y /1.000000000001/
print *, x, y, x .eq. y
end
! The trailing digit is lost
! The trailing digit is lost
! So x is considered equal to y
! The trailing digit is lost
! The trailing digit is preserved
! So x and y are considered different
program testdpc
call nodpc
call dpc
end
When compiled, this program prints the following:
1.000000000 1.00000000000000000 T
1.000000000 1.00000000000100009 F
showing that with -qdpc the extra precision is preserved.
Related Information
“-qautodbl Option” on page 134 and “-qrealsize Option” on page 222 are more
general-purpose options that can also do what -qdpc does. -qdpc has no effect if
you specify either of these options.
152 XL Fortran Enterprise Edition for AIX : User’s Guide