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XMVECTOR comparisons won't work in debug mode

2 posts in this topic

EDIT:  I didn't mean to post this three times.  It gave me an error the first two tries and I didn't realize it went through anyway.


XMVECTOR comparisons such as XMVectorNearEqual or XMVectorGreater are not working in debug mode, but they work in release mode.
An example:




    XMVECTOR test1 = XMVectorSet(1, 1, 1, 1);
    XMVECTOR test2 = XMVectorSet(1, 1, 1, 1);
    XMFLOAT4 nearEqualTest;
    XMStoreFloat4(&nearEqualTest, XMVectorNearEqual(test1, test2, XMVectorReplicate(.01f)));
    if(nearEqualTest.x == 0xFFFFFFFF)



This code correctly exits in release mode, but not debug.  It shows up as -1.QNAN 


For reference, this is the function documentation


Edited by Vexal

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That function sets the bits of each component to the integer value of 0xFFFFFFFF. Your "if(nearEqualTest.x == 0xFFFFFFFF)" equality test will promote 0xFFFFFFFF to a float, which won't be the same value as integer 0xFFFFFFFF being reinterpreted as a float (the bits 0xFFFFFFFF actually don't form a valid floating point number, which is why you get -1.QNAN in the debugger). The reason 0xFFFFFFFF is used as the result is so that it can be used as a mask for subsequent SIMD mask operations that choose a particular value based on your conditional. DirectXMath exposes this functionality using XMVectorSelect.


If in doubt you should always look at the implementation of DirectXMath functions, since they're all inline in a the .h/.inl files.


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