Re: Using 128-bit integers for sum, avg and statistics aggregates

On 03/10/2015 02:26 AM, Peter Geoghegan wrote:
> On Mon, Mar 9, 2015 at 5:37 PM, Andreas Karlsson <andreas(at)proxel(dot)se> wrote:
>> int128-agg-v7.patch
>
> I see a spelling error:
>
> "+ * On platforms which support 128-bit integers some aggergates instead use a"

Fixed.

> I think you should talk about the new thing first (just after the
> extant, first sentence "Integer data types use Numeric..."). Refer to
> where 128-bit integers are used and how, and only then the other stuff
> (exceptions). After that, put the PolyNumAggState struct definition
> and basic functions. Then int2_accum() and so on.

Good idea! Do you think the rewritten comment is clear enough, or do I
need to go into more detail?

/*
* Integer data types use Numeric accumulators to share code and avoid risk
* of overflow. To speed up aggregation 128-bit integer accumulators are
* used instead where sum(X) or sum(X*X) fit into 128-bits, and there is
* platform support.
*
* For int2 and int4 inputs sum(X) will fit into a 64-bit accumulator,
hence
* we use faster special-purpose accumulator routines for SUM and AVG of
* these datatypes.
*/

#ifdef HAVE_INT128
typedef struct Int128AggState

--
Andreas Karlsson