linux-kernel - Re: [PATCH] Introduce ext4_find_next

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Date:	Fri, 21 Sep 2007 12:13:13 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
CC:	akpm@...ux-foundation.org, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Introduce ext4_find_next_bit

Aneesh Kumar K.V wrote:
> Also add generic_find_next_le_bit
> 
> This gets used by the ext4 multi block allocator patches.
> 

Looks like it's a straight forward on Little Endian Architectures.
I see something for powerpc, what about other architectures?

> 
> +unsigned long generic_find_next_le_bit(const unsigned long *addr, unsigned
> +		long size, unsigned long offset)
> +{

Docbook style comments on the function and arguments would be nice.

> +	const unsigned long *p = addr + BITOP_WORD(offset);
> +	unsigned long result = offset & ~(BITS_PER_LONG - 1);
> +	unsigned long tmp;
> +
> +	if (offset >= size)
> +		return size;
> +	size -= result;
> +	offset &= (BITS_PER_LONG - 1UL);
> +	if (offset) {
> +		tmp = ext2_swabp(p++);
> +		tmp &= (~0UL << offset);
> +		if (size < BITS_PER_LONG)
> +			goto found_first;
> +		if (tmp)
> +			goto found_middle;
> +		size -= BITS_PER_LONG;
> +		result += BITS_PER_LONG;
> +	}
> +
> +	while (size & ~(BITS_PER_LONG - 1)) {
> +		tmp = *(p++);
> +		if (tmp)
> +			goto found_middle_swap;
> +		result += BITS_PER_LONG;
> +		size -= BITS_PER_LONG;
> +	}
> +	if (!size)
> +		return result;
> +	tmp = ext2_swabp(p);
> +found_first:
> +	tmp &= (~0UL >> (BITS_PER_LONG - size));
> +	if (tmp == 0UL)		/* Are any bits set? */
> +		return result + size; /* Nope. */
> +found_middle:
> +	return result + __ffs(tmp);
> +
> +found_middle_swap:
> +	return result + __ffs(ext2_swab(tmp));
> +}
> +EXPORT_SYMBOL(generic_find_next_le_bit);
> +
>  #endif /* __BIG_ENDIAN */


-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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