Imposing a hard limit on Python integers

[storchaka (Serhiy Storchaka)]

@oscarbenjamin

I presume that this really only actually changes anything in a 32-bit build because otherwise size_t would already be 64 bits anyway right? So basically this is just making the type bigger on 32 bit system so that the code can be simpler?

No, it only affects 64-bit platforms. I just made bit counts 64-bit on all platforms, this solves issues on 32-bit platforms (it required only 0.5 GB to create an integer whose size in bits exceeds size_t).

What I propose here, is to change the limit on 64-bit platforms. Currently it is about 2^{63} bytes or 2^{66} bits. I propose to reduce it to about to 2^{63} or 2^{64} bits (2^{60} or 2^{61} bytes). Both limits are insanely large and exceed the maximum size of addressable memory on most of current platforms.

@oscarbenjamin

Does there exist a supported platform where size_t is more than 64 bits?

Even if they exist, Python is not a right tool to work with exbibyte-size integers.
Even adding two of such integers will take yeasr.

Well, it seems that there are no objections. I am not still sure about using signed or unsigned 64-bit integers, but this detail will be discussed on GitHub and in the C API Workgroup.