Would making plain int 64-bit break a lot of reasonable code?

Question

Until recently, I\'d considered the decision by most systems implementors/vendors to keep plain int 32-bit even on 64-bit machines a sort of expedient wart. With mo

Answer 1

DEC Alpha and OSF/1 Unix was one of the first 64-bit versions of Unix, and it used 64-bit integers - an ILP64 architecture (meaning int, long and pointers were all 64-bit quantities). It caused lots of problems.

One issue I've not seen mentioned - which is why I'm answering at all after so long - is that if you have a 64-bit int, what size do you use for short? Both 16 bits (the classical, change nothing approach) and 32 bits (the radical 'well, a short should be half as long as an int' approach) will present some problems.

With the C99 and headers, you can code to fixed size integers - if you choose to ignore machines with 36-bit or 60-bit integers (which is at least quasi-legitimate). However, most code is not written using those types, and there are typically deep-seated and largely hidden (but fundamentally flawed) assumptions in the code that will be upset if the model departs from the existing variations.

Notice Microsoft's ultra-conservative LLP64 model for 64-bit Windows. That was chosen because too much old code would break if the 32-bit model was changed. However, code that had been ported to ILP64 or LP64 architectures was not immediately portable to LLP64 because of the differences. Conspiracy theorists would probably say it was deliberately chosen to make it more difficult for code written for 64-bit Unix to be ported to 64-bit Windows. In practice, I doubt whether that was more than a happy (for Microsoft) side-effect; the 32-bit Windows code had to be revised a lot to make use of the LP64 model too.