I am working with a large Fortran code that uses XLF compiler for Power7
It uses these flags to set the precision to 64bit: -qrealsize=8 -qintsize=8
However a recently imported piece of code has lines similar to this:
real :: var1d(nvol)
real :: var3d(ni,nj,nk)
var1d = var3d*1.0e6
I wonder how XLF is dealing with the literal 1e6?
Main concern is; this is where a reference version and a modified version
deviate. The 9th and 10th significant figures are different for var1d.
Nastily this grows with iterations.
Data Object REALSIZE(4) in Effect REALSIZE(8) in Effect ------------------------------------------------------------------- 1.2 REAL(4) REAL(8) 1.2e0 REAL(4) REAL(8) 1.2d0 REAL(8) REAL(16) 1.2q0 REAL(16) REAL(16) REAL REAL(4) REAL(8) DOUBLE PRECISION REAL(8) REAL(16) COMPLEX COMPLEX(4) COMPLEX(8) DOUBLE COMPLEX COMPLEX(8) COMPLEX(16)
As stated in the on-line XLF manual. Thanks for all the useful suggestions. SO I will have to confirm this is not the source of discrepancy.