Re: [Boost-users] How to find: best integer type for processor

On Thu, Oct 30, 2008 at 8:41 AM, Cory Nelson wrote:

On Thu, Oct 30, 2008 at 8:24 AM, Daryle Walker wrote:

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Is there a macro and/or typedef that will tell me bit-length used for a processor and/or the best integer type for said processor? The "int" type is supposed to be that type, and it was in the 16- and 32-bit eras. (I learned C programming with the former in the... early 1990s!) However, the powers-that-be decided, for "backwards compatibility," to freeze "int" and "long" at 32 bits and use a new type, "long long," for 64 bits, which should be the optimized integer type for 64-bit processors. (If they kept to the plan, "int" would be 64 bits, "long" either 64 or 128, "short" up to 32, and the new type will be "short short" at 16.) I want to know the best type so, when I build multi-integer arrays for various purposes, I don't pick an element type that causes a slow down, whether to focus on a fraction of a register (if the chosen type is too small) to handle two registers at once (if the chosen type is too large).

Most things don't need 64-bit ints, so it would just be wasting memory to use them if 32-bit ints are as fast or faster. This is why "int" stays 32-bit on most x64 ABIs.

IMO, on a 64-bit CPU int should be 64 bits, and long should be 128 bits, except if adding two 64-bit values that are already in registers is slower than if they were 32-bit. I don't buy the argument that this wastes memory. When a given integer type uses too much memory for your needs, you can store a smaller type in your structs; you can even use bitfields if you need a portable way to tinker with an integer's memory footprint. Emil Dotchevski Reverge Studios, Inc. http://www.revergestudios.com/reblog/index.php?n=ReCode