RIricardobeat·Jul 27, 2019
Lines 19 and 27 in the source: https://github.com/lemire/Code-used-on-Daniel-Lemire-s-blog/...
In How fast can a BufferedReader read lines in Java?lemire
Code-used-on-Daniel-Lemire-s-blog
C++2012–2026
lemire / Code-used-on-Daniel-Lemire-s-blog
Code-used-on-Daniel-Lemire-s-blog
This is a repository for the code posted on my blog
21Distinct people
23Mentions
0Explicit recommenders
970GitHub stars
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This is a repository for the code posted on my blog
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This week on Hacker News
Nov 8–Nov 15 UTC · Direct repository links and separately labeled related project stories. Indexed through 11/15/2026, 9:01:12 PM UTC.
No direct repository links were found in the indexed HN discussions over the past seven days. Older discussions are available below.
Mentions over time
HN mentions by year23 dated mentions
Observed mentions: 2012-07-24 00:16:38 UTC to 2026-05-23 10:17:41 UTC.
* An incomplete calendar period is marked with an outlined bar. Its count is not directly comparable with a full period.
Counts come from the repository’s dated source evidence. Index cutoff: 2026-11-02 08:16:59 UTC.
View mention counts and date ranges
| Period | Start (UTC) | End (exclusive, UTC) | Mentions | Submissions | Comments |
|---|---|---|---|---|---|
| 2012 | 2012-01-01 00:00:00 UTC | 2013-01-01 00:00:00 UTC | 2 | 0 | 2 |
| 2013 | 2013-01-01 00:00:00 UTC | 2014-01-01 00:00:00 UTC | 0 | 0 | 0 |
| 2014 | 2014-01-01 00:00:00 UTC | 2015-01-01 00:00:00 UTC | 0 | 0 | 0 |
| 2015 | 2015-01-01 00:00:00 UTC | 2016-01-01 00:00:00 UTC | 0 | 0 | 0 |
| 2016 | 2016-01-01 00:00:00 UTC | 2017-01-01 00:00:00 UTC | 2 | 0 | 2 |
| 2017 | 2017-01-01 00:00:00 UTC | 2018-01-01 00:00:00 UTC | 0 | 0 | 0 |
| 2018 | 2018-01-01 00:00:00 UTC | 2019-01-01 00:00:00 UTC | 1 | 0 | 1 |
| 2019 | 2019-01-01 00:00:00 UTC | 2020-01-01 00:00:00 UTC | 4 | 0 | 4 |
| 2020 | 2020-01-01 00:00:00 UTC | 2021-01-01 00:00:00 UTC | 1 | 0 | 1 |
| 2021 | 2021-01-01 00:00:00 UTC | 2022-01-01 00:00:00 UTC | 4 | 0 | 4 |
| 2022 | 2022-01-01 00:00:00 UTC | 2023-01-01 00:00:00 UTC | 1 | 0 | 1 |
| 2023 | 2023-01-01 00:00:00 UTC | 2024-01-01 00:00:00 UTC | 4 | 0 | 4 |
| 2024 | 2024-01-01 00:00:00 UTC | 2025-01-01 00:00:00 UTC | 3 | 0 | 3 |
| 2025 | 2025-01-01 00:00:00 UTC | 2026-01-01 00:00:00 UTC | 0 | 0 | 0 |
| 2026 (partial) | 2026-01-01 00:00:00 UTC | 2027-01-01 00:00:00 UTC | 1 | 0 | 1 |
What Hacker News says
4 sourcesThe current winner is a SIMD-ish solution using 32 bit math as 4 8-bit lanes. This has been added to the repo, and is discussed in the comments.
https://github.com/lemire/Code-used-on-Daniel-Lemire-s-blog/...
In Parsing short hexadecimal strings efficientlyHis code https://github.com/lemire/Code-used-on-Daniel-Lemire-s-blog/... does not use OpenMP.
Different benchmarks favor different processors… Here's another one, now multi-threaded
My quick run of `sysbench cpu` (something with prime numbers) shows:
Skylark 3.3GHz 32core (at Packet; Ubuntu 18.04):
events per second: 44287.87
Zen 3.85GHz 8c16t (my desktop; FreeBSD 13-CURRENT):
events per second: 14632.61
And with a single thread, 1386.24 vs 1740.91. Divided by clock speed, it's about 93% of the performance.
In Ampere EMAG 64bit Arm WorkstationI think Daniel's use of the word "separate" in "separate and expensive" is ill-advised, as it implies a critique of ARM's ISA design in a way that isn't relevant for this case. One might be concerned if you needed all 128 bits in some other use, but not here.
As for loading large constants, if you read the post and follow the link at "reuse my benchmark" (https://github.com/lemire/Code-used-on-Daniel-Lemire-s-blog/...) you will see that these functions as measured are inside hot loops. As such, presumably constant loading is very likely to be hoisted out of these loops on both architectures.
This will make the considerably slower UMULH stick out like a sore thumb. Also note that the measurement loop allows most of the work of each iteration to be done in parallel - the work of the rng is a long dependency chain within the calculation but
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the update of the seed is quick and independent of that.
I would guess that the Ampere box has a wretchedly slow multiply. In a comment on the post, Daniel finds an ugly performance corner on A57 (possibly related, possibly not): "On a Cortex A57 processor, to compute the most significant 64 bits of a 64-bit product, you must use the multiply-high instructions (umulh and smulh), but they require six cycles of latency and they prevent the execution of other multi-cycle instructions for an additional three cycles."