From: Denis Vlasenko <vda@port.imtp.ilyichevsk.odessa.ua>
To: Matt Mackall <mpm@selenic.com>, Andrew Morton <akpm@osdl.org>,
       "Theodore Ts'o" <tytso@mit.edu>
Subject: Re: [PATCH 1/12] random pt4: Create new rol32/ror32 bitops
Date: Tue, 25 Jan 2005 23:02:55 +0200
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On Friday 21 January 2005 23:41, Matt Mackall wrote:
> --- rnd2.orig/include/linux/bitops.h	2005-01-19 22:57:54.000000000 -0800
> +++ rnd2/include/linux/bitops.h	2005-01-20 09:20:24.641660815 -0800
> @@ -134,4 +134,26 @@
>  	return sizeof(w) == 4 ? generic_hweight32(w) : generic_hweight64(w);
>  }
>  
> +/*
> + * rol32 - rotate a 32-bit value left
> + *
> + * @word: value to rotate
> + * @shift: bits to roll
> + */
> +static inline __u32 rol32(__u32 word, int shift)
> +{
> +	return (word << shift) | (word >> (32 - shift));
> +}
> +
> +/*
> + * ror32 - rotate a 32-bit value right
> + *
> + * @word: value to rotate
> + * @shift: bits to roll
> + */
> +static inline __u32 ror32(__u32 word, int shift)
> +{
> +	return (word >> shift) | (word << (32 - shift));
> +}
> +
>  #endif

gcc generates surprisingly good assembly for this,
I coudn't beat it for 32bit rotations. Cool!

So you are absolutely right here with not trying
to asm optimize it.

OTOH 64bit gcc rol is worse.
--
vda

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