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Date: Sat, 21 Aug 2004 21:46:32 -0700
From: "David S. Miller" <davem@redhat.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: torvalds@osdl.org, akpm@osdl.org, linux-kernel@vger.kernel.org,
       rlrevell@joe-job.com
Subject: Re: [patch] context-switching overhead in X, ioport(), 2.6.8.1
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FWIW, I would recommend a sparse bitmap implementation for the
ioport stuff.  Something simple like:

struct set_ent {
	u32 pos;
	u32 bits;
	struct set_ent *next;
};

static inline int is_set(struct set_ent *head, int pos)
{
	while (head != NULL) {
		if (pos >= head->pos) {
			if (pos < head->pos + 32) {
				if (head->bits &
				    (1 << (pos - head->pos)))
					return 1;
			}
			break;
		}

		head = head->next;
	}
	return 0;
}

You get the idea.