linux-kernel - Re: [PATCH v7 0/5] Update LZ4 compressor module

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Date:   Thu, 9 Feb 2017 12:05:40 +0100
From:   Sven Schmidt <4sschmid@...ormatik.uni-hamburg.de>
To:     Eric Biggers <ebiggers3@...il.com>
Cc:     Minchan Kim <minchan@...nel.org>, akpm@...ux-foundation.org,
        bongkyu.kim@....com, rsalvaterra@...il.com,
        sergey.senozhatsky@...il.com, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, herbert@...dor.apana.org.au,
        davem@...emloft.net, linux-crypto@...r.kernel.org,
        anton@...msg.org, ccross@...roid.com, keescook@...omium.org,
        tony.luck@...el.com
Subject: Re: [PATCH v7 0/5] Update LZ4 compressor module

Hey Eric,

On Wed, Feb 08, 2017 at 09:24:25PM -0800, Eric Biggers wrote:
> Also I noticed another bug, this time in LZ4_count():
> 
> > #if defined(CONFIG_64BIT)
> > #define LZ4_ARCH64 1
> > #else
> > #define LZ4_ARCH64 0
> > #endif
> ...
> > #ifdef LZ4_ARCH64
> >        if ((pIn < (pInLimit-3))
> >                && (LZ4_read32(pMatch) == LZ4_read32(pIn))) {
> >                pIn += 4; pMatch += 4;
> >        }
> > #endif
> 
> Because of how LZ4_ARCH64 is defined, it needs to be '#if LZ4_ARCH64'.
> 
> But I also think the way upstream LZ4 does 64-bit detection could have just been
> left as-is; it has a function which gets inlined:
> 
> 	static unsigned LZ4_64bits(void) { return sizeof(void*)==8; }
> 
> Eric

does this apply for LZ4_isLittleEndian() as well? As a reminder:
	
	static unsigned LZ4_isLittleEndian(void)
	{
		/* don't use static : performance detrimental */
		const union { U32 u; BYTE c[4]; } one = { 1 };

		return one.c[0];
	}

It is surely easier to read and understand using these functions in favor of the macros.

Thanks,

Sven