64 bit - How to also prepare for 64-bits when migrating to Delphi 2010 and Unicode

Question

As 64 bits support is not expected in the next version it is no longer an option to wait for the possibility to migrate our existing code base to unicode and 64-bit in one go. However it would be nice if we could already prepare our code for 64-bit when doing our unicode translation. This will minimize impact in the event it will finally appear in version 2020. Any suggestions how to approach this without introducing to much clutter if it doesn't arrive until 2020?

Answer 1

There's another similar question, but I'll repeat my reply here too, to make sure as many people see this info:

First up, a disclaimer: although I work for Embarcadero. I can't speak for my employer. What I'm about to write is based on my own opinion of how a hypothetical 64-bit Delphi should work, but there may or may not be competing opinions and other foreseen or unforeseen incompatibilities and events that cause alternative design decisions to be made.

That said:

• There are two integer types, NativeInt and NativeUInt, whose size will float between 32-bit and 64-bit depending on platform. They've been around for quite a few releases. No other integer types will change size depending on bitness of the target.

• Make sure that any place that relies on casting a pointer value to an integer or vice versa is using NativeInt or NativeUInt for the integer type. TComponent.Tag should be NativeInt in later versions of Delphi.

• I'd suggest don't use NativeInt or NativeUInt for non-pointer-based values. Try to keep your code semantically the same between 32-bit and 64-bit. If you need 32 bits of range, use Integer; if you need 64 bits, use Int64. That way your code should run the same on both bitnesses. Only if you're casting to and from a Pointer value of some kind, such as a reference or a THandle, should you use NativeInt.

• Pointer-like things should follow similar rules to pointers: object references (obviously), but also things like HWND, THandle, etc.

• Don't rely on internal details of strings and dynamic arrays, like their header data.

• Our general policy on API changes for 64-bit should be to keep the same API between 32-bit and 64-bit where possible, even if it means that the 64-bit API does not necessarily take advantage of the machine. For example, TList will probably only handle MaxInt div SizeOf(Pointer) elements, in order to keep Count, indexes etc. as Integer. Because the Integer type won't float (i.e. change size depending on bitness), we don't want to have ripple effects on customer code: any indexes that round-tripped through an Integer-typed variable, or for-loop index, would be truncated and potentially cause subtle bugs.

• Where APIs are extended for 64-bit, they will most likely be done with an extra function / method / property to access the extra data, and this API will also be supported in 32-bit. For example, the Length() standard routine will probably return values of type Integer for arguments of type string or dynamic array; if one wants to deal with very large dynamic arrays, there may be a LongLength() routine as well, whose implementation in 32-bit is the same as Length(). Length() would throw an exception in 64-bit if applied to a dynamic array with more than 232 elements.

• Related to this, there will probably be improved error checking for narrowing operations in the language, especially narrowing 64-bit values to 32-bit locations. This would hit the usability of assigning the return value of Length to locations of type Integer if Length(), returned Int64. On the other hand, specifically for compiler-magic functions like Length(), there may be some advantage of the magic taken, to e.g. switch the return type based on context. But advantage can't be similarly taken in non-magic APIs.

• Dynamic arrays will probably support 64-bit indexing. Note that Java arrays are limited to 32-bit indexing, even on 64-bit platforms.

• Strings probably will be limited to 32-bit indexing. We have a hard time coming up with realistic reasons for people wanting 4GB+ strings that really are strings, and not just managed blobs of data, for which dynamic arrays may serve just as well.

• Perhaps a built-in assembler, but with restrictions, like not being able to freely mix with Delphi code; there are also rules around exceptions and stack frame layout that need to be followed on x64.