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Comment by Wowfunhappy | Hacker News Reader

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Wowfunhappy·

I'm a little confused: is X32 support different from 32-bit x86 support, a la 32 bit mode in Windows?

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Yes, it's different.

32-bit x86 support is for compatibility with older software.

x32 is a completely new thing that has nothing to do with compatibility. Basically, it's everything that AMD added to the 64-bit variant of x86, except the actual 64bit pointers. So you get more registers, access to additional instructions, and so on.

Yes. It's essentially x86_64 but with all addresses being 32-bits, so you get all the things like extra registers that x86_64 added without the added memory bloat of longer addresses for everything.

What "bloat"? It's curious to see that when a technique comes out and is being misunderstood by the masses and praised as the best thing since sliced bread. Suddenly robustness, accountability and predictability turn into "bloat". Do you have a real world example?

If you double the size of pointers (64 bit, up from 32 bit) then your program will take up more heap. This is especially significant for languages where everything is a heap allocation.

If you code does intresive computation with structures containing a lot of pointers, you’ll get much more cache miss when using 64 but pointers.

The performance hit can be quite heavy!

Cache is a limited resource, and you want as many pointers as possible to fit there.

It's bloat used properly, in the most literal sense. Your pointers are 64bit, but you always use less than 32bits. So, all your pointers are twice is big. This wasted space from bits you do not need is "bloat".

Yes. x32 uses the 64-bit registers of x86-64 but retains a 32-bit pointer representation. x86-32 does not have any access to 64-bit registers.

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