The Old New Thing

When corporate policies meet precision scientific equipment

December 15, 2014 Dec 15, 2014 12/15/14
Raymond Chen
One of my colleagues used to work as an IT consultant, and one of his clients was a tobacco company. Since they were a tobacco company, the company policy on smoking was "You can smoke anywhere, any time." "Anywhere" includes the labs. The labs with very expensive precision scientific equipment. My colleague told me that this policy meant ...

Notes on calculating constants in SSE registers

December 15, 2014 Dec 15, 2014 12/15/14
Raymond Chen
There are a few ways to load constants into SSE registers. Load them from memory. Load them from general purpose registers via . Insert selected bits from general purpose registers via . Try to calculate them in clever ways. Loading constants from memory incurs memory access penalties. Loading or inserting them from general ...

Detecting whether a SID is well-known SID

December 12, 2014 Dec 12, 2014 12/12/14
Raymond Chen
You might think that the function would tell you whether a SID is well-known, but it doesn't. Rather, it tells you whether a SID exactly matches the well-known SID you specified. For example, you can ask, "Is this the Authenticated Users SID?" or "Is this the Everyone SID?" But you can't ask, "Is this any type of well-known SID?" I guess ...

What states are possible in a DRAWITEMSTRUCT structure?

December 11, 2014 Dec 11, 2014 12/11/14
Raymond Chen
The structure has an member which contains a number of bits describing the state of the item being drawn. How do those states map to the underlying control? Most of the states are rather obvious. For a list box item to be selected, it means that the item is part of the selection. But what does selected mean for a button? Since people like ...

If you get a procedure address by ordinal, you had better be absolutely sure it's there, because the failure mode is usually indistinguishable from success

December 10, 2014 Dec 10, 2014 12/10/14
Raymond Chen
A customer reported that the function was behaving strangely. We have this code in one of our tests: Recently, this test started failing in bizarre ways. When we stepped through the code, we discovered that ends up calling instead of . The first time we try to test , we get stack corruption because has a different function prototype...

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

December 8, 2014 Dec 8, 2014 12/8/14
Raymond Chen
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 any processor you...

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

December 5, 2014 Dec 5, 2014 12/5/14
Raymond Chen
Calling to cancel a window timer prevents messages from being generated for that timer, even if one is overdue. In other words, give this sequence of operations: no message is ever generated. Even though a timer became due during the , no timer message was generated during the sleep because timer messages are generated on demand, and ...