The default is always nonzero.
After doing this, the data aligned nicely.
This option is supported only by the C++ front end, and the information is generally only useful to the G++ development team.
The only supported options are predecrement and postincrement.
Specifically: corrections for irregular slit widths, and pixel-by-pixel detector sensitivity variations.
The purpose of this mode is to specify what kind of addressing is allowed, on machines where the allowed kinds of addressing depend on the machine mode being addressed.