Re: Re: [Portable-clx] bit-bash-copy gone

On Sun, Apr 03, 2005 at 01:27:25AM +0300, Nikodemus Siivola wrote:
> On Sat, 2 Apr 2005, Christophe Rhodes wrote:
> 
> >Nikodemus Siivola <[email protected]> writes:
> >
> >>-       (sb-kernel:bit-bash-copy sdata src-idx ddata dest-idx width)))))
> >>+       (sb-kernel:ub8-bash-copy sdata src-idx ddata dest-idx width)))))
> >
> >Are you sure that ub8-bash-copy is the right one?  Without having
> 
> Though on second thought, _if_ the old bit-bash-copy was built on memcpy, 
> then presumably it dealt with octets? (Forwarded to sbcl-devel so that 
> nfroyd can comment on this, maybe.)

Hmmm, this change is causing a lot of problems. :)

If you used BIT-BASH-COPY for data movement, you probably want to use
UB1-BASH-COPY, since that's a drop-in replacement for BIT-BASH-COPY.
If, however, you know the width of the data you're copying (e.g. in
SB-MD5, we are always copying bytes), then a different UBFOO-BASH-COPY
function makes more sense and will require less massaging of the
arguments.

Changing CLX to use the new functions is fun because BIT-BASH-COPY is
used in several different places without regard to the underlying
width of the elements being copied.  The Right Thing would be to switch
on the width of the arguments and use the appropriate copying function.

Incidentally, BIT-BASH-COPY was not built on top of memcpy; you're
probably thinking of %BYTE-BLT, which was introduced because
BIT-BASH-COPY has issues with the number of bits that can be copied
at once (although after modifying the code, I think that limit is
artificial).  Now that we have copy functions for multiple widths (in
particular, byte-sized widths), this limit should no longer be an
issue and %BYTE-BLT could be removed.
-- 
Nathan | From Man's effeminate slackness it begins.  --Paradise Lost

The last good thing written in C was Franz Schubert's Symphony Number 9.
                                               --Erwin Dieterich


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