On 10 Apr 2007, at 08:52, Jonas Maebe wrote:
Note that doing this may cause problems with packed arrays and records, like we had in FPC. If you treat 0..3 as signed, then you can no longer pack it in 2 bits using the current format used by FPC and GPC. The reason is that if a type is signed, both compilers treat the uppermost bit of a packed value as the sign bit. So 2 and 3 would be interpreted as -2 and -1, respectively.
Of course, it is possible to change the format of packed values (e.g., always store them as unsigned, with a bias of -lower_bound in case of signed types), but this may cause backward compatibility issues.
Or, alternatively, you can of course do the sign extension only if the lower bound is < 0 rather than if the type is signed (maybe that even already happens today in gpc that way). Depending on how the gpc internals work, differentiating between "signed type" and "lower bound < 0" may cause some hairiness.
It's mainly something you simply have to keep in mind when performing such a change, I guess.
Jonas