Quirk | drop quantum circuit simulator that runs in your browser

Here goes a solution that will center an element (image or graph) on-click event in the viewport - the browser window.
Please note for small changes (for better image display): _SL500_.jpg and img.style.width = 'auto';.

Instead of two separate mouse-down and up operations, you could try this according to puppeteer docs:

Instead of the double quoted column name, use backquote

I think here is the official issue for your question:

https://github.com/PowerShell/PowerShell/issues/14036

I think the best workaround is $table.(6).count

But I am curious what is the worst that can happen in a realistic system if one ignores this rule. A segmentation fault? an overflow of pointer arithmetic? unnecessary paginations?

Wasted space.

To be able to form the address "one before" you need to have the space available. For example, if you have a 1k struct, it must start at least 1k from the beginning of memory. On a small device with limited memory, or an x86 with segmented memory, that can be tricky.

To form a "one past" pointer/iterator you only need one byte beyond the end. As it cannot be dereferenced anyway, there is no need to have space for an entire object, just the possibility to form the address.

From the comments:

At the time the rules were defined, we had real CPUs with dedicated address registers that validated the address against the segment size on register load. That made sure that a -1 address would trap...

https://en.wikipedia.org/wiki/Motorola_68000#Architecture

This ruled out the case of having "one before" wrapping around to the end of the segment. Because if the segment is small, the resulting end might not be there.

The problem is you are constructing the ImageViewer with another QGraphicsView that you made in Qt Designer, "qgraphic_image", as its parent. This makes it a child widget inside of that parent graphics view, and it's effectively invisible as its viewport rect has no size (that is why you got a division by 0 error).

You can remove the "qgraphic_image" from your UI file, for now I just replaced it in the layout to try it:

[basic.start.main]/4:

If std​::​exit is called to end a program during the destruction of an object with static or thread storage duration, the program has undefined behavior.

I have the same problem with Android Studio Arctic Fox. Even I created a Hello world project, the option in your screenshot does not work for me. I believe there was some change in the test configuration with gradle test runner in android 4.3. Currently I will use the following as work around

1. Select one of the test class and right click to run it with Gradle Test Runner
2. Change the argument as --tests "com.*" in the current configuration to run all the test

The smaller 256B size not seeing a drop from the L2 streamer might be due to the sequence of cache misses being too short to activate the streamer and waste bandwidth (and slots in the LFBs and L2 <-> L3 superqueue) on requests that won't be useful.

For aligned 4k, there are no bytes within the same page that you're not fetching, so the L2 prefetcher is positively useful, or at least not harmful. (Demand loads come in pretty quickly for later lines when running memcpy so I'm guessing speeds were about the same with/without HW prefetch enabled, unless HW prefetch helps getting started on a new 4k chunk while still waiting for the end of the previous.)

The L2 only sees physical addresses, and AFAIK it doesn't try to prefetch across a 4k boundary. (Even if its within the same 2M hugepage, because it doesn't know that either.) The "next-page prefetcher" Intel mentions being new in Ivy Bridge is AFAIK just a TLB prefetch, not data.

So with aligned 4k memcpy, HW prefetch stops automatically at the end of the data you're actually going to read, not wasting any bandwidth. Since mmap gives you page-aligned memory, these 4k memcopies are from a single source page.

(The destination is irrelevant as it probably stays hot in L1d cache, with maybe an occasional eviction to L2, and the reload from it after memcpy can come from store-forwarding, not even having to wait for memcpy's store to commit to L1d.)

Prediction: If your smaller memcpy source starts part way into a 4k page, but still end at the end of a 4k page, you'd probably see similar behaviour to prefetch disabled. e.g. generate a random page number, and start at 3072 bytes into it, doing a 1 KiB copy. So all your 1 KiB copies come from the ends of pages, never middles.

(You'd still have more dTLB misses per byte memcpyed, because each TLB entry is only covering 1 K of the data you ever actually read. You did you use MAP_POPULATE so you shouldn't be seeing page faults in the timed region, assuming you have enough RAM.)

L1d KiB /L2 MiB /L3 MiB -- 512 / 16 / 22

Those are aggregate totals, but L1d and L2 are private per-core! You have 32kiB L1d and 1MiB L2 per core, because this is Cascade Lake, same layout as Skylake-X.

And BTW, I'd consider using a fast PRNG like xorshift+ or xorshift* inside the timing loop; that's easily random enough to defeat prefetching; even a simple LFSR or even LCG with a power-of-2 modulo would do that (and be very cheap, just an imul and add). It avoids having to read offsets from another array, if you really want to isolate just the memcpy memory accesses. Probably doesn't make a difference though. One advantage of a very simple PRNG with a period equal to the space you're trying to cover (like an LCG) is that you won't generate the same address twice, giving you a random permutation of the blocks. But with a big enough block of memory, random cache hits even from L3 are unlikely even without that hard-to-achieve property.

Your current array of offsets is fine. (I didn't look at the code super closely, so I'm just assuming there aren't bugs.)