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[Octave-bug-tracker] [bug #60928] Performance of sort unexpectedly slow
From: |
Rik |
Subject: |
[Octave-bug-tracker] [bug #60928] Performance of sort unexpectedly slow for DIM=2 |
Date: |
Mon, 16 Aug 2021 12:45:14 -0400 (EDT) |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.101 Safari/537.36 |
Follow-up Comment #12, bug #60928 (project octave):
Okay, the slowdown is entirely due to this piece of code
for (octave_idx_type j = 0; j < iter; j++)
{
octave_idx_type offset = j;
octave_idx_type offset2 = 0;
while (offset >= stride)
{
offset -= stride;
offset2++;
}
offset += offset2 * stride * ns;
For dimension 1, stride is 1 and offset = j will take the values 1 .. 125,000
for my benchmark data. So for the last calculation, the code reduces to a
while loop that executes 125,000 times simply to increment offset2.
I assume that the original coder was trying to calculate
offset = floor (j / stride) * stride * ns;
in such a way as to avoid conversion to double and to avoid actual division
operation. However, this is causing real problems.
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- [Octave-bug-tracker] [bug #60928] Performance of sort unexpectedly slow for DIM=2, Rik, 2021/08/14
- [Octave-bug-tracker] [bug #60928] Performance of sort unexpectedly slow for DIM=2, Rik, 2021/08/14
- [Octave-bug-tracker] [bug #60928] Performance of sort unexpectedly slow for DIM=2, Michael Leitner, 2021/08/15
- [Octave-bug-tracker] [bug #60928] Performance of sort unexpectedly slow for DIM=2, Michael Leitner, 2021/08/15
- [Octave-bug-tracker] [bug #60928] Performance of sort unexpectedly slow for DIM=2, Rik, 2021/08/16
- [Octave-bug-tracker] [bug #60928] Performance of sort unexpectedly slow for DIM=2,
Rik <=
- [Octave-bug-tracker] [bug #60928] Performance of sort unexpectedly slow for DIM=2, Rik, 2021/08/16
- [Octave-bug-tracker] [bug #60928] Performance of sort unexpectedly slow for DIM=2, Rik, 2021/08/16
- [Octave-bug-tracker] [bug #60928] Performance of sort unexpectedly slow for DIM=2, anonymous, 2021/08/16
- [Octave-bug-tracker] [bug #60928] Performance of sort unexpectedly slow for DIM=2, Michael Leitner, 2021/08/16
- [Octave-bug-tracker] [bug #60928] Performance of sort unexpectedly slow for DIM=2, anonymous, 2021/08/16
- [Octave-bug-tracker] [bug #60928] Performance of sort unexpectedly slow for DIM=2, anonymous, 2021/08/16
- [Octave-bug-tracker] [bug #60928] Performance of sort unexpectedly slow for DIM=2, Rik, 2021/08/16
- [Octave-bug-tracker] [bug #60928] Performance of sort unexpectedly slow for DIM=2, anonymous, 2021/08/16
- [Octave-bug-tracker] [bug #60928] Performance of sort unexpectedly slow for DIM=2, Rik, 2021/08/17
- [Octave-bug-tracker] [bug #60928] Performance of sort unexpectedly slow for DIM=2, Rik, 2021/08/17