Re: faster strcpy()

David Woodhouse (Dave@imladris.demon.co.uk)
Fri, 24 Apr 1998 11:14:34 +0200

> > while(*a++=*b++); perhaps?
>
> No, that's how it was before. This copies byte at time and is slow.
> memcpy is fast. If we could use the same technique as memcpy uses
> to copy strings and at the same time check the terminating 0...
> I don't see the answer myself, does anybody see?

I was just trying to remember it. The answer was written on a scrap of paper by
my Director of Studies, during a supervision near the end of last term, and I
_really_ ought to be able to remember it :)

It's something like subtracting 0x01010101 from the dword and oring with
0x80808080 to detect the carry, but that's not quite it. Perhaps you do
something like

((a - 0x01010101) xor a) & 0x808080

but I thought it was simpler than that.

---- ---- ----
David Woodhouse, Robinson College, CB3 9AN, England. (+44) 0976 658355
Dave@imladris.demon.co.uk http://www.imladris.demon.co.uk
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