Re: [using gcc book] 5.20 double-word integers

[Chris Devers <cdevers at pobox dot com>]

Following closely the note I just sent...


On Tue, 26 Aug 2003, Chris Devers wrote:

> On Tue, 26 Aug 2003, Gabriel Paubert wrote:
>
> > On Sat, Aug 23, 2003 at 09:33:34PM -0400, Chris Devers wrote:
> > > Hello again,
> > >
> > > In chapter five, section 5.9 (Double-Word Integers) of the _Using GCC_
> > > book, we have the following sentence:
> > >
> > >     Multiplication is open-coded if the machine supports
> > >     fullword-to-doubleword a widening multiply instruction.
> > >
> > > I feel this would read more clearly if written as follows:
> > >
> > >     Multiplication is open-coded if the machine supports a
> > >     widening fullword-to-doubleword multiply instruction.
> >
> > Warning: nitpicking ahead.
> >
> > On PPC32 at least, there is no widening multiply instruction, but
> > there is a multiply high instruction which allows to easily compute
> > all the necessary terms and is used for that purpose.
>
> Do you feel this warrants a change in phrasing? Was the original version
> any more accurate? The sentence is already written in terms of a caveat
> ("...foo if bar..."); are you saying that this caveat should be further
> qualified for PPC32 (etc?) targets?
>
> Suggested rephrasings are welcome.

Here's how that paragraph reads now:

<excerpt>

You can use these types in arithmetic like any other integer types.
Addition, subtraction, and bitwise boolean operations on these types are
open-coded on all types of machines.  Multiplication is open-coded if the
machine provides an instruction which provides the most significant half
of the product.  Division and shifts are open-coded only on machines that
provide special support.  The operations that are not open-coded use
special library routines that come with GCC@.

</excerpt>

This revision takes into account Gabriel Paubert's suggestion for how to
clarify & update the third sentence ("Multiplication is open-coded..."),
but his earlier mail expressed reservations about whether the phrasing he
suggested (which is substantially what I've used here) was either accurate
or clear enough.

Any thoughts? Thanks...


-- 
Chris Devers    cdevers@pobox.com

superstition, n.
An irrational belief or ritual which survives until replaced by a more
effective superstition. The replacement is known as "updating the
system documentation." See also -MANCY, PRAYER.

    -- from _The Computer Contradictionary_, Stan Kelly-Bootle, 1995