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Date: Wed, 14 Mar 2001 20:30:25 -0500
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 <E166E69A95753648BC398E36BE9A3AB80C99B155@sus-ma1it06.rational.com>
From: "Corey Ashford" <corey@rational.com>
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 <3AAFE967.44BAEDAD@averstar.com>
 <snSr6.2653$y47.570666@news2-win.server.ntlworld.com>
 <fy7y9u8hs24.fsf@whitelion.org>
Subject: Re: RISC
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Date: 2001-03-14T20:30:25-05:00
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"Fraser Wilson" <fraser@whitelion.org> wrote in message news:fy7y9u8hs24.fsf@whitelion.org...
> "chris.danx" <chris.danx@ntlworld.com> writes:
>
> > *   procedure set_data (reg  : in out register;
> > *                                  data : in word) is
> > *   begin
> > *      -- and this!
> > *      reg.data := ((reg.data / 65536) * 65536) xor long_word(data);
> > *   end set_data;
>
>
> If that's inefficient, what about
>

As a side note, I would bet that most compilers would optimize
the line above to (using C shift terminology):

reg.data := ((reg.data >> 16) << 16) xor long_word(data);

I know the Apex compiler would.  If the divisor and/or multiplier are not numbers or named numbers, then the compiler
would not be able to do that optimization, however.

Similarly, a mod operation with a number that's a power of
two would be optimized to an AND operation with the proper
mask.


- Corey

>     reg.data := (reg.data and 16#FFFF0000) or register_block (data);

>
> > *      -- i've got to improve the efficiency of this;
> > *     reg.data := ((reg.data / 256) * 256 ) xor register_block(data);
>
> Similarly,
>     reg.data := (reg.data and 16#FFFFFF00#) or register_block (data);
>
> Fraser.