Re: [Qemu-devel] [PATCH] include: Add a comment to explain the origin of sizes' lookup table

[Eric Blake <eblake@redhat.com>]

On 11/2/18 8:58 PM, Leonid Bloch wrote:
> The lookup table for power-of-two sizes was added in commit 540b8492618eb
> for the purpose of having convenient shortcuts for these sizes in cases
> when the literal number has to be present at compile time, and
> expressions as '(1 * KiB)' can not be used. One such case is the
> stringification of sizes. Beyond that, it is convenient to use these
> shortcuts for all power-of-two sizes, even if they don't have to be
> literal numbers.
> 
> Despite its convenience, this table introduced 55 lines of "dumb" code,
> the purpose and origin of which are obscure without reading the message
> of the commit which introduced it. This patch fixes that by adding a
> comment to the code itself with a brief explanation for the reasoning
> behind this table. This comment includes the short AWK script that
> generated the table, so that anyone who's interested could make sure
> that the values in it are correct (otherwise these values look as if
> they were typed manually).
> 
> Signed-off-by: Leonid Bloch <lbloch@janustech.com>
> ---
>   include/qemu/units.h | 18 ++++++++++++++++++
>   1 file changed, 18 insertions(+)

I'm still not completely sold that we can't come up with a more elegant 
runtime solution that avoids the need for hard-coding stringified 
defaults at compile time; but if we keep these S_* constants, this 
comment definitely helps.

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
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