Horton

Re: Optimize numeric multiplication for one and two base-NBASE digit multiplicands.

Joel Jacobson <joel@compiler.org>

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From: "Joel Jacobson" <joel@compiler.org>
To: "Dean Rasheed" <dean.a.rasheed@gmail.com>
Cc: Dagfinn Ilmari Mannsåker <ilmari@ilmari.org>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2024-07-02T19:55:19Z
Lists: pgsql-hackers 
On Tue, Jul 2, 2024, at 20:53, Joel Jacobson wrote:
> Trying to wrap my head around what could cause this.
>
> It's rounding down instead of up, and these cases all end with decimal .500XXXX.

Interesting, I actually think there is a bug in the normal mul_var() code.
Found a case that rounds down, when it should round up:

Calling mul_var() with:
var1=51.2945442386599
var2=0.828548712212
rscale=0

returns 42, but I think it should return 43,
since 51.2945442386599*0.828548712212=42.5000285724431241296446988

But maybe this is expected and OK, having to do with MUL_GUARD_DIGITS?

/Joel

Commits

  1. Optimise numeric multiplication for short inputs.

  2. Optimise numeric division for 3 and 4 base-NBASE digit divisors.

  3. Optimise numeric division for one and two base-NBASE digit divisors.