Re: Re: Unsigned Problems Revisited

On Thu, 2002-10-24 at 09:51, David M. Lloyd wrote: > On Thu, 24 Oct 2002, Andi Gutmans wrote: > > > At 02:49 PM 10/23/2002 -0500, David M. Lloyd wrote: > > > > >The reality of twos-complement, bitwise arithmatic is that there are > > >three basic shift operations: shift left, bitwise shift right, and > > >arithmetic shift right. This simple fact is one of the basic ideas of > > >dealing with twos-complement integers. > > > > I know that but I still wanted the opposite to be available to keep > > things symmetrical. I'm not sure but I think CPU's do support both > > logical and arithmetic shifts and just do the same with both (I might be > > wrong though). > > Generally no, it's a waste of opcode space for modern CISC processors. > RISC processors often have integrated barrel-shifters, so they don't need > shift instructions at all. > > Intel carries over "arithmetic" shift right instructions from older > architetures for backwards-compatibility with x86, but their RISC > implementation (Itanium) does not contain support for the operation. > > One RISC example is ARM. They give you four shift options: Logical left, > logical right, arithmetic right, and rotate right. Making the operation > symmetrical is a waste of precious bit combinations, and would have meant > either losing another shift operation or else adding another bit to the > shift operation specifier, which means that another bit would have to be > sacrificed elsewhere. > > Another example is SPARC, which implements shifting with discrete > instructions, only implents one left shift operator. PowerPC does not > implement it either. Alpha has 3 instructions as well (log left, log right, arith right) > > >Given this fact, there is no reason to have a bogus fourth operator in the > > >name of symmetry. Mathematical operaters are simply not always > > >symmetrical. There is no such thing as 'arithmetic shift left' or > > >'logical shift left' in terms of twos-complement integers, so why invent > > >it? > > > > I agree that they don't *have* to be symmetrical but I think it's > > better. > > Better why? Anyone who understands twos-complement will understand (and > expect) the ability to do those three operations, and will not be > surprised by the lack of two left shifts. I argue that they *should NOT* > be symmetrical because it is wrong. I have to say I agree, introducing a bogus operator could actually cause confusion. Java, which has been used several times in past arguments of "why we should not do XYZ", has not had a problem with having only the operators that actually exist. > > >Second of all, my understanding of the here-doc operator is that it acts > > >as a unary operation. I don't see the conflict with the binary > > >application of <<<, given the example of unary and binary -, if it is > > >absolutely neccessary to fulfill the (somewhat psychotic) need for > > >symmetry where it is not realy needed, or even strictly correct. > > > > psychotic? Can we please have discussions on a professional and not > > personal level? > > It is true though, unless you can give me a sound mathematical reason that > the ops should exist... and saying "it looks right" or "it is easier" is > not a valid reason, becuase to those with even basic twos-complement math > background, it looks wrong and is not easier. > > > As far as I remember it does clash with here-docs. I'm pretty sure I > > thought of an example a while back. I can try and think of one again. In > > any case, I wouldn't want an overloaded operator. We try and keep away > > of that kind of stuff with PHP. Clashing can occur with Constant values, and functions with a \n in front of the (). > Very well... then let's not put in the nonsense operator, and just have > three shift operations: <<, >>, and >>>. I agree > - D > > <dmlloyd@tds.net> > > > -- > PHP Development Mailing List <http://www.php.net/> > To unsubscribe, visit: http://www.php.net/unsub.php > -Jason -- Jason T. Greene <jason@inetgurus.net> <jason@php.net>