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From: JBS@IBM.COM
Newsgroups: comp.arch
Subject: bizarre instructions
Message-ID: <9102210042.AA12291@ucbvax.Berkeley.EDU>
Date: 21 Feb 91 00:14:02 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Lines: 34


          Herman Rubin says:
Do you mean to tell me that computations involving both integers and
floating-point numbers are not important?  Or that dividing floats by
floats, obtaining an integer quotient and a floating remainder, likewise?
That particular step is the first step of any trigonometric or exponential
function computation when it is not known in advance that the argument is
small.  There are other periodic and related functions for which this is
useful.  It would also speed up interpolation, etc.

          Since argument reduction for the trigonometric functions is
done in practice by multiplying by 1/pi I do not see how it would ben-
efit from your proposed instruction.  I believe this instruction would
have little general utility.
          An efficient way to do the fortran "x=dint(y)" is important.
This is lacking on the Risc System 6000 as was pointed out in a Los
Alamos report.  By the way is it true that it is impossible to
reasonably express this in ADA?
        Peter Montgomery says:
        Yes, most programs are written in these languages.
As Dan says, the language designers made mistakes.  During one
review period for Fortran 90, I requested an operation which
takes four nonnegative integers a, b, c, n with
a < n or b < n (c is optional and defaults to 0).
The requested operation returns q and/or r, where

                a*b + c = q*n + r   and   0 <= r < n

        Why didn't you ask for an integer*8 data type?  Wouldn't
that give you what you want and have much more general utility?
        I would like an instruction which counts the number of ones in
the binary representation of an integer but I find it hard to argue
that this would be widely used.
                    James B. Shearer