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From: Arnd Bergmann <arnd@arndb.de>
To: Bob Copeland <me@bobcopeland.com>
Subject: Re: [PATCH 5/7] omfs: add bitmap routines
Date: Fri, 28 Mar 2008 04:51:10 +0100
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On Thursday 27 March 2008, Bob Copeland wrote:

> +static int nibblemap[] = {4, 3, 3, 2, 3, 2, 2, 1, 3, 2, 2, 1, 2, 1, 1, 0};
> +
> +unsigned long omfs_count_free(struct super_block *sb)
> +{
> +	unsigned int i, j, count = 0;
> +	unsigned char *map;
> +	unsigned long sum = 0;
> +	struct omfs_sb_info *sbi = OMFS_SB(sb);
> +
> +	for (i = 0; i < sbi->s_imap_size; i++) {
> +		map = (unsigned char *) sbi->s_imap[i];
> +		for (j = 0; j < sb->s_blocksize &&
> +			count + j < sbi->s_num_blocks/8; j++)
> +			sum += nibblemap[map[j] & 0xf] +
> +				nibblemap[(map[j] >> 4) & 0xf];
> +		count += sb->s_blocksize;
> +	}
> +	return sum;
> +}

I think it would be helpful to express this using hweight64.