Dynamic arrays allocation size

["Luís]

On Tuesday, 26 March 2013 at 21:00:43 UTC, Brad Roberts wrote:
> The bias towards x86 is less than the bias towards standard 
> integer sizes.  D explicitly ignores platforms with odd sizes.  
> D does NOT support byte where byte is outside the range 
> -127..128.  Etc.

Brad, if the overflow/underflow was undefined behavior you could 
easily map D types into the machine's weird native types with 
little performance loss. So, in that sense, D would support 
"platforms with odd sizes".  Even as is I'm sure D *can*  support 
those unconventional platforms, it just has a performance penalty 
to assure that the exact semantics are followed, because there 
isn't a completely direct map between the native 
instructions/registers and D's type model.

Just because a D byte is mapped into a 10-bit register does not 
mean the language is supporting bytes outside of the [-128, +127] 
range. The question is if the compiler has to add extra 
instruction to ensure if the overflow behavior of the 
registers/CPU instructions matches the language overflow 
behavior. If the overflow behavior was undefined then the 10-bit 
register would be a direct implementation of D's byte. Since it 
isn't undefined, and the register presumably wraps at 10 bits, 
then the compiler has to emit extra code, to model the behavior 
of an 8-bit two's-complement variable in a 10-bit register.