Re: C compiler pointer management on DSPs

On Thursday, February 27, 2020 at 7:03:27 PM UTC-8, rob...@dodo.com.au wrote:
> On 2020-02-28 09:23, gah4@u.washington.edu wrote:
>
> > Machines not so well designed require masking off the appropriate
> > bits before operating with them.


(snip)


> Who can say that the CDC machines (7600; 70 series, etc) were not
> well designed?


> They were intended to be fast, and to carry out operations on
> words (of 60 bits).


CDC machines are designed for fast floating point number crunching.


They are not necessarily designed for fast character manipulation,
as that is supposed to be a relatively small part of the work.


The hardware/software tradeoffs were different so many years ago.


My favorite one has always been how the IBM 704 (and I believe
later 36 bit machines) read in cards. The read row-wise, each row
into two 36 bit words, leaving off 8 columns. This is also the reason
why Fortran (fixed form) uses columns 1-72.


Anyway, after the compiler reads in a card row-wise, it has to
convert to columnwise (six characters per word), including converting
to the appropriate character code. But it presumably saves a lot of
logic in the card reader, where it would be expensive and could be
done in software. The 7094 was the high-end number cruncher at
the time, including its use for S/360 emulation during its development.


But actually, as well as I know, the more usual way to run such
machines was to copy cards to tape, presumably in a cheaper machine,
so that the fast machine didn't waste so much time.


I don't know about the 60 bit machines, but there are stories
about C compilers for Cray machines using 64 bit char.


As with the CDC machines, Cray machines are designed for fast floating
point, and not so fast for fixed point.
[This is getting rather far from compilers but would be totally on-topic
in alt.folklore.computers. -John]

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