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From: =?utf-8?Q?Dagfinn_Ilmari_Manns=C3=A5ker?= <ilmari@ilmari.org>
To: "Joel Jacobson" <joel@compiler.org>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Optimize numeric multiplication for one and two base-NBASE
 digit multiplicands.
References: <44d2ffca-d560-4919-b85a-4d07060946aa@app.fastmail.com>
Date: Mon, 01 Jul 2024 13:25:08 +0100
In-Reply-To: <44d2ffca-d560-4919-b85a-4d07060946aa@app.fastmail.com> (Joel
	Jacobson's message of "Mon, 01 Jul 2024 08:04:06 +0200")
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"Joel Jacobson" <joel@compiler.org> writes:

> Hello hackers,
>
> Attached patch introduces an optimization of mul_var() in numeric.c,
> targeting cases where the multiplicands consist of only one or two
> base-NBASE digits. Such small multiplicands can fit into an int64 and
> thus be computed directly, resulting in a significant performance
> improvement, between 26% - 34% benchmarked on Intel Core i9-14900K.
>
> This optimization is similar to commit d1b307eef2, that also targeted
> one and two base-NBASE digit operands, but optimized div_var().

div_var() also has an optimisation for 3- and 4-digit operands under
HAVE_INT128 (added in commit 0aa38db56bf), would that make sense in
mul_var() too?

> Regards,
> Joel

- ilmari