On Tuesday, 22 July 2014 at 21:06:09 UTC, Artur Skawina via
Digitalmars-d wrote:
D is defined as it is, with wrapping two's complement integer
arithmetic
and defined integer sizes.
Integer promotion is locked to 32 bits. That is a mistake. Why
wrap everything below 32bit at 32 on a 64 bit ALU? That's
inconvinient and will lead to undetected bugs.
I also think it is a mistake to lock to C rules, which were
defined when multiply often were done in software. In most modern
ALUs a N bit multiply yields a 2*N bit result. Why discard the
high word?
With forced wrapping/masking (a*b)>>32 is turned into
((a*b)&0xffffffff)>>32 which is zero, so you have to cast 'a' to
64 bit before the multiply, then downcast the result to 32 bit.
My point is that the language must be consistent; adding special
cases would create a language in which one expression yields
several
different results, depending on evaluation context.
I understand this point, but I think code that would yield such
errors most lkely is buggy or underspecified.
Ola.
