[Courses] One last diversion on binary, and then I'll shut up for a while.

[jim]

    The C keyword that may help is register; there are 
compiler command-line options that let one set some 
kinds of optimization such as fast or compact or .... 
    Can anyone provide helpful details? 



On Wed, 2012-03-07 at 10:54 -0900, Christopher Howard wrote:
> On 03/07/2012 10:18 AM, Kevin Cole wrote:
> > 
> >> It would be great if you explain the significance of 64 bit processors in
> >> *your style*. Your rambling is welcome. :-)
> >>
> > 
> > Interesting choice of words there: "significance" as in you almost answered
> > your own question. ;-) Really not a lot to say here. More bits = more
> > "significant" digits in mathematical calculations, a larger potential
> > vocabulary for your machine language, and the ability to address more
> > memory, because now the processor "goes to 11" ;-) Since it can "count
> > higher" it can handle addresses that are further away from location 0, and
> > if each possible value is a potential code for an instruction, well, more
> > instructions are possible.  So, operations that used to require multiple
> > machine language instructions to get a job done may now require only one,
> > because the designers added the equivalent of a contraction to the
> > vocabulary list.
> > 
> > The architectures are designed to "chunk" groups of bits together as
> > "words" to handle work more efficiently.  The size of the chunks are
> > limited by the laws of physics and economics -- how small can the
> > components be made, how much heat will they generate, how much does it cost
> > to manufacture them? That said, if you have something that exceeds the
> > limits of the the "word size" computers generally find a kludge to handle
> > such problems... up to a point.  Shrinking back down to our more managable
> > model of the 4-bit word on our eensy-weensy computer that can handle
> > numbers from 0 to 15, if the language is designed to accommodate you, when
> > you want to work with numbers up to, oh say, 31, it has the ability to do
> > summersaults while juggling to use two words together.  Generally slower
> > than a system designed to handle larger word sizes.
> 
> This is, of course, true on the fundamental level. Note than in an
> actual 64 bit architecture, speaking specifically of the amd64
> architecture, the improvements are more profound. In amd64, you get 15
> of the 256-bit YMM registers, meaning it is possible to operate on 256
> bits of data at once if you know the right instructions to pass in.
> 
> Furthermore (again, in the case of the amd64 architecture) there are a
> number of additional improvements that are quite significant in terms of
> code efficiency. In particular, the amd64 architecture gets an
> additional 8 general purpose registers (GPRs) and 8 SSE registers. This
> is really helpful as it means that more working data (e.g., function
> variables and parameters) can be stored in these really fast registers,
> rather than being constantly pulled in and out of memory (which is
> relatively speaking quite slow). Seven of the new GPRs are not affected
> implicitly by any other process operations, meaning they are really
> convenient to use if you happen to be programming in assembly.
> 
> Some of these advantages are automatically leveraged by your compiler.
> However, some are not and require you to know how to use them.
> 
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