MIAMEX function MX_AS3264 (200) returns the architecture of the A-Shell executable, 32 or 64 bit.
xcall MIAMEX, MX_AS3264, bits
Parameters
bits (num) [out]
32 or 64
Note that for prior A-Shell versions, attempting to call this function will generate a pop-up invalid opcode error message, so if you are coding to be 32/64 bit aware, you should first check the A-Shell version, perhaps using the function Fn'MinAshVer() found in fnminasver.bsi SOSLIB:[907,10]. It's safe to assume that any A-Shell version below 1708 is 32 bit or less.