Re: which way is faster?

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On Mon, 2006-12-18 at 17:12 -0500, Ming Zhang wrote:
> See this code piece
> 
> http://lxr.linux.no/source/drivers/scsi/libata-scsi.c?v=2.6.18#L1049
> 
> 1056         lba |= ((u64)scsicmd[2]) << 24;
> 1057         lba |= ((u64)scsicmd[3]) << 16;
> 1058         lba |= ((u64)scsicmd[4]) << 8;
> 1059         lba |= ((u64)scsicmd[5]);
> 
> it can also be written as 
> 
> lba = be32_to_cpu(*(u32 *)(&scsicmd[2])
> 
> 
> i wrote a simple code to test this and i found second one is several
> time faster than first one.
> 
> if there any pitfall with 2nd way?

personally I find the original code a lot more clear in what the intent
of it is.

The device/command give you a set of BYTES, and they get pieced together
into a meaning here... 

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