linux-kernel - Re: [RFC] LZO de/compression support

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Message-ID: <4cefeab80705300347gc618151we40a0cd34e6460ff@mail.gmail.com>
Date:	Wed, 30 May 2007 16:17:54 +0530
From:	"Nitin Gupta" <nitingupta910@...il.com>
To:	"Jan Engelhardt" <jengelh@...ux01.gwdg.de>
Cc:	lkml <linux-kernel@...r.kernel.org>, linux-mm-cc@...top.org,
	linuxcompressed-devel@...ts.sourceforge.net,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Daniel Hazelton" <dhazelton@...er.net>,
	"Richard Purdie" <richard@...nedhand.com>,
	"Bret Towe" <magnade@...il.com>,
	"Satyam Sharma" <satyam.sharma@...il.com>
Subject: Re: [RFC] LZO de/compression support - take 6

On 5/30/07, Jan Engelhardt <jengelh@...ux01.gwdg.de> wrote:
>
> On May 30 2007 11:24, Nitin Gupta wrote:
> >>
> >> It is the bytestream (ip) that is reinterpreted as uint16_t.
> >> And I really doubt that the LZO author has a big-endian machine,
> >> given the days of ubiquitous x86.
> >
> >> le16_to_cpu it is.
> >
> > But then why you think it should be
> > le_16_cpu() -- how will this make any difference?
>
> Like I said, we are reinterpreting the byte stream as a uint16_t
> (= reading from bytestream to CPU). While writing out an uint16_t
> as a bytestream is cpu_to_le16.
>

I didn't properly understand this. But you seem to be correct - now I
ran sparse check:

* using cpu_to_le16()
lib/lzo1x/lzo1x_decompress.c:141:35: error: incompatible types for
operation (>>)
lib/lzo1x/lzo1x_decompress.c:141:35:    left side has type restricted
unsigned short [usertype] [force] <noident>
lib/lzo1x/lzo1x_decompress.c:141:35:    right side has type int
lib/lzo1x/lzo1x_decompress.c:140:20: error: incompatible types for operation (-)
lib/lzo1x/lzo1x_decompress.c:140:20:    left side has type unsigned
char *register [assigned] op
lib/lzo1x/lzo1x_decompress.c:140:20:    right side has type bad type
lib/lzo1x/lzo1x_decompress.c:157:35: error: incompatible types for
operation (>>)
lib/lzo1x/lzo1x_decompress.c:157:35:    left side has type restricted
unsigned short [usertype] [force] <noident>
lib/lzo1x/lzo1x_decompress.c:157:35:    right side has type int
lib/lzo1x/lzo1x_decompress.c:156:11: error: incompatible types for
operation (-=)


* using le16_to_cpu()
lib/lzo1x/lzo1x_decompress.c:140:23: warning: cast to restricted type
lib/lzo1x/lzo1x_decompress.c:156:14: warning: cast to restricted type

But still, how do I get rid of these two warnings? or, do these
warning suggest some real problem that still exist in code?

- Nitin


> > For your ref (from big_endian.h):
> > # define __cpu_to_le16(x) ((__force __le16)__swab16((x)))
> > # define __le16_to_cpu(x) __swab16((__force __u16)(__le16)(x))
>
>
>         Jan
> --
>
-
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