Feedback-ID: ic6394509:Fastmail
User-Agent: Cyrus-JMAP/3.11.0-alpha0-566-g3812ddbbc-fm-20240627.001-g3812ddbb
MIME-Version: 1.0
Message-Id: <31b8386d-4bcb-4909-b7da-bbeb9a8ece55@app.fastmail.com>
In-Reply-To: <32510d71-8c00-4896-9c11-5ea4b3c01ffc@app.fastmail.com>
References: <44d2ffca-d560-4919-b85a-4d07060946aa@app.fastmail.com>
 <87zfr1e1uj.fsf@wibble.ilmari.org>
 <9ff90ff9-5ac1-4529-b2f4-f93b37734b9c@app.fastmail.com>
 <81348268-b9fd-4308-bf52-056070aa7c2a@app.fastmail.com>
 <f25ddfc8-4f02-4e8f-8e74-0532f48d0817@app.fastmail.com>
 <CAEZATCV2qPTGo2Fd8xDs06Q7iU5aorgSa9+Fw9zkuQv1y15rcw@mail.gmail.com>
 <8e909218-1965-4515-99e3-4bb5b625e004@app.fastmail.com>
 <CAEZATCWEou=NjpvS-r1WxymbAYihsdKQoQBj1HfBeocoNcv5Ww@mail.gmail.com>
 <bbc62c2d-1173-4454-9e17-be99437c0e7e@app.fastmail.com>
 <0459ded5-6daf-4bf0-9ab0-e1f11ab15ec6@app.fastmail.com>
 <CAEZATCW+N9qaE=5_1xcB0isMrirojN=Bd0yY4Pw67iji4swYiQ@mail.gmail.com>
 <4e54bf4f-59fe-4c9a-b446-a2b64cbfd584@app.fastmail.com>
 <fb6e4aa6-54e1-4be4-a7f6-3edc99aa7e6e@app.fastmail.com>
 <27d42b25-f328-4231-9db0-3811dc77c8cf@app.fastmail.com>
 <33c51978-8ee8-438c-9804-e46c0ca8f3f9@app.fastmail.com>
 <CAEZATCUA+GBYvzbqSr7LPDDfmr24jQE1R0iyYfjFk82xeuBCRw@mail.gmail.com>
 <018dd6e8-8f21-4b3b-8d80-2d128f6d00b4@app.fastmail.com>
 <CAEZATCUnn2JK4gSrymvmkhy_qsGybKv0-n0CTnLcfwfVNfTE7g@mail.gmail.com>
 <32510d71-8c00-4896-9c11-5ea4b3c01ffc@app.fastmail.com>
Date: Wed, 03 Jul 2024 22:45:34 +0200
From: "Joel Jacobson" <joel@compiler.org>
To: "Dean Rasheed" <dean.a.rasheed@gmail.com>
Cc: =?UTF-8?Q?Dagfinn_Ilmari_Manns=C3=A5ker?= <ilmari@ilmari.org>,
 pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Optimize numeric multiplication for one and two base-NBASE digit
 multiplicands.
Content-Type: text/plain
Archived-At: <https://www.postgresql.org/message-id/31b8386d-4bcb-4909-b7da-bbeb9a8ece55%40app.fastmail.com>
Precedence: bulk

On Wed, Jul 3, 2024, at 22:27, Joel Jacobson wrote:
> On Wed, Jul 3, 2024, at 20:57, Dean Rasheed wrote:
>> I wouldn't expect it to ever be off by more than 1, given that
>> MUL_GUARD_DIGITS = 2, which corresponds to 8 decimal digits, and the
>> number of digits in the smaller input (and hence the number of digit
>> products in each column) is limited to something like 16,000 NBASE
>> digits.
>
> OK, so then the cases I found where it was off by 2 for the mul_var_int() patch
> are unexpected?

Sorry, I meant off by 2 for the mul_var_small() patch, these cases that I found:

       var1        |      var2      | rscale_adjustment |   result   | numeric_mul_patch_small
-------------------+----------------+-------------------+------------+-------------------------
     8952.12658563 | 0.902315486665 |               -16 |  8077.6425 |               8077.6423
    0.881715409579 | 0.843165739371 |               -16 | 0.74343223 |              0.74343221
    0.905322758954 | 0.756905996850 |               -16 | 0.68524423 |              0.68524421
 8464.043170546608 | 0.518100129611 |               -20 |  4385.2219 |               4385.2217
 5253.006296984449 | 0.989308019355 |               -20 |  5196.8413 |               5196.8411
(5 rows)

Regards,
Joel