March 2014 | The Old New Thing

A puzzle involving dynamic programming, or maybe it doesn't

Raymond ChenMarch 31, 2014Mar 31, 201403/31/14

Here's a programming challenge: Evaluate the following recurrence relation efficiently for a given array [x0, …, xn−1] and integer k. Hint: Use dynamic programming. In words: If the array has only two elements, then the result is the average of the two elements. If the array has more than two elements, then ...

The dangers of buffering up posted messages and then reposting them later

Raymond ChenMarch 28, 2014Mar 28, 201403/28/14

A customer wanted to check that their idea for solving a re-entrancy problem doesn't have any hidden gotchas. We have a window which processes incoming work. One of our work items enters a modal loop, and if new work gets posted to the window while the modal loop is running, our work manager gets re-entered, and Bad Things happen. Our ...

Functions that return GDI regions rarely actually return regions

Raymond ChenMarch 27, 2014Mar 27, 201403/27/14

For reasons I don't quite understand, the only functions in GDI and USER which create GDI regions are the functions with Create in their name, like CreateRectRgn or CreatePolygonRgn. All the other functions which return a region require you to pass an existing region to use as the output. I can see this being useful for ...

Can CoCreateGuid ever return GUID_NULL?

Raymond ChenMarch 26, 2014Mar 26, 201403/26/14

A customer asked whether the CoCreateGuid function can ever return GUID_NULL. Their code uses GUID_NULL for special purposes, and it would be bad if that was ever returned as the GUID for an object. "Can we assume that CoCreateGuid never returns GUID_NULL? Or should we test the return value against GUID_NULL, and if it is ...

Geeky t-shirt alert: Windows 7's so-called God Mode

Raymond ChenMarch 25, 2014Mar 25, 201403/25/14

Back in 2010, the so-called God Mode was the hit discovery of the Internet, at least until the next cute cat video made the rounds. If you had stopped by the Microsoft Visitor Center during that meme's brief moment in the sun, and wandered into the gift shop, you could have picked up a t-shirt that said {ED7BA470-8E54-465E-825C-99712043E01C...

Enumerating set partitions with Bell numbers and Stirling numbers of the second kind

Raymond ChenMarch 24, 2014Mar 24, 201403/24/14

Just for fun, today's Little Program is going to generate set partitions. (Why? Because back in 2005, somebody asked about it on an informal mailing list, suggesting it would be an interesting puzzle, and now I finally got around to solving it.) The person who asked the question said, Below we show the partitions of [4]. The periods ...

Different senses of scale create different travel expectations

Raymond ChenMarch 21, 2014Mar 21, 201403/21/14

A friend of mine had a business meeting near London, and he decided to extend it to a tour of Scotland and England once the meetings were over. (This is the same friend who took me on the emergency vacation many years ago.) His plan was to rent a car early one morning and drive from the meeting location all the way up to Aberdeen at one go, ...

Why can't I __declspec(dllexport) a function from a static library?

Raymond ChenMarch 21, 2014Mar 21, 201403/21/14

A customer was having trouble exporting a function with the __declspec(dllexport) declaration specified, but found that if the function was in a static library, no function was exported. Why is that? Let's go back to the classical model for linking. Code is pulled from a LIB file only if the linker encounters a reference to it. If ...

When visitors to the United States underestimate the size of the country

Raymond ChenMarch 20, 2014Mar 20, 201403/20/14

A friend of mine who is from Lebanon (but now lives in Seattle) invited his grandmother to come visit for the summer. When she arrived, he asked her, "Grandma, is there anywhere in particular you would like to visit?" His grandmother replied, "I'd like go to to Washington, DC." "Okay, Grandma. Let me buy some plane tickets." "No, let's ...

Going for the facts: Who is displaying this message box?