[PATCH] add memrchr(3)

[Yaakov (Cygwin/X)]

On Wed, 2012-05-09 at 08:23 -0600, Eric Blake wrote: 
> sizeof(unsigned char) is defined by C to be exactly 1; I always
> question code that spells it out longhand instead of using 1.

But, but, magic numbers! :-) Not that I care either way here.

> >>       if (src > src_end) >> 	break;
> 
> Also, src will never be > src_end - memchr returns NULL rather than
> reading beyond the bounds of length.

Actually, it *was* returning values beyond src_end and the effects
weren't pretty, hence the check.

> Additionally, I think that searching forwards through the array via one
> function call per occurrence of the byte in question is wasteful -
> since we already know the array bounds, we might as well search in
> reverse by doing a single C loop that iterates backwards over a word at
> a time. strrchr must search forwards, because it is also searching for
> the terminating NUL and doesn't know the length in advance, but memrchr
> should be faster.

Fair enough, so code duplication it is then.  Revised source file
attached.


Yaakov
Cygwin/X

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