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Re: bitpack search in bitsets

From: Akim Demaille
Subject: Re: bitpack search in bitsets
Date: Wed, 18 Nov 2020 07:06:58 +0100


> Le 17 nov. 2020 à 22:50, Bruno Haible <bruno@clisp.org> a écrit :
> Hi Akim,
> In gnulib/lib/ssfmalloc-bitmap.h there is a function
> /* Returns the smallest index k >= 0 for which the bit packet of c consecutive
>   bits (1 <= c <= 32) is all set in the bitmap consisting of num_words words.
>   Returns (size_t)(-1) if there is none.  */
> I can easily extend this to c > 32. So, this will be a one-pass search for
> c consecutive bits in a bitmap, that operates on words and fetches every word
> only twice at most.
> Is this something that could be useful for your 'bitset' module?

(FTR, I am not the author, Michael Hayes is.  It was a contribution
for GCC, that actually didn't make it into GCC.  But I liked it very much
and took it for Bison.)

That doesn't ring any bell.  I don't remember I saw any feature in bitset
that depends on consecutive set bits, and a quick search did not find

Conversely: couldn't ssfmalloc sit on top of bitset?

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