December 2014 | Page 3 of 3 | The Old New Thing

Creating double-precision integer multiplication with a quad-precision result from single-precision multiplication with a double-precision result

Raymond ChenDecember 8, 2014Dec 8, 201412/8/14

Suppose you want to multiply two double-word values producing a quad-word result, but your processor supports only single-word multiplication with a double-word result. For concreteness, let's say that your processor supports 32 × 32 → 64 multiplication and you want to implement 64 × 64 → 128 multiplication. (Sound like a

Killing a window timer prevents the WM_TIMER message from being generated for that timer, but it doesn't retroactively remove ones that were already generated

Raymond ChenDecember 5, 2014Dec 5, 201412/5/14

Calling KillTimer to cancel a window timer prevents WM_TIMER messages from being generated for that timer, even if one is overdue. In other words, give this sequence of operations: no WM_TIMER message is ever generated. Even though a timer became due during the Sleep, no timer message was generated during the sleep because timer messa

If my WM_TIMER handler takes longer than the timer period, will my queue fill up with WM_TIMER messages?

Raymond ChenDecember 4, 2014Dec 4, 201412/4/14

A customer was worried that they may have a problem with their message queue filling with WM_TIMER messages. "If my WM_TIMER handler takes longer than the timer period, will my queue fill up with WM_TIMER messages?" As we should know by now, timer messages are generated on demand: The WM_TIMER message is a low-priority message. The Get

What happens if I don't paint when I get a WM_PAINT message?

Raymond ChenDecember 3, 2014Dec 3, 201412/3/14

Suppose your window procedure doesn't paint when it gets a WM_PAINT message. What happens? It depends on how you don't paint. If you have an explicit handler for the WM_PAINT message that does nothing but return without painting, then the window manager will turn around and put a new WM_PAINT message in your queue. "And try harder this ti

Microspeak: Redlines

Raymond ChenDecember 2, 2014Dec 2, 201412/2/14

To the outside world, redline can mean to mark something for removal, or it could mean the maximum safe speed of an engine. But in the world of Microsoft design, the term redlines (pronounced as if it were written as the two words red lines, but the accent is on the red) refers to a diagram showing the exact position of visual elements. They

Counting array elements which are below a particular limit value using SSE

Raymond ChenDecember 1, 2014Dec 1, 201412/1/14

Some time ago, we looked at how doing something can be faster than not doing it. That is, we observed the non-classical effect of the branch predictor. I took the branch out of the inner loop, but let's see how much further I can push it. The trick I'll employ today is using SIMD in order to operate on multiple pieces of data simultaneousl

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