Re: [9fans] integer width on AMD64 (was: Re: AMD64 system)

[Charles Forsyth <charles.forsyth@gmail.com>]

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The MIPS, PowerPC and SPARC all grew to 64 bits from 32 bits, so 32 bit
quantities
(and usually but not always 16 bit and 8 bit quantities) have suitable
instructions to fetch them.
Exceptions include ARM, where the original 32 bit architecture made byte
access (in the C style at least)
expensive, but they corrected that in (I think) v4 by adding byte
instructions. Alpha might have
been an exception too, but that's dead.

accesses aren't "unaligned" when they are smaller than the machine word,
but when the address isn't a multiple of the length accessed. Plan 9
generally keeps
things properly aligned. Processors don't usually have trouble with
accesses smaller than
the machine word.

On 7 May 2012 11:01, dexen deVries <dexen.devries@gmail.com> wrote:

> on RISC, there's usually significant penalty for accessing data units
> smaller
> than machine word (`unaligned access'), but it ain't so on the benevolent
> x86
> CISC.
>

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