how to convert C code in LabVIEW

[kevin_khan]

Hi there I have a quicik question.  i have a line of C code that I am trying to implement in LabVIEW and I was wondering if someone could show me how to do so.  The following is the line of code that i am trying to implement:

if ((temp = temp1 & (unsigned) 0xFFF) & 800)

       temp = temp - 4096

Where temp is 16 bit signed and temp1 is 16 bit unsigned.

This line of code is meant to perform a sign extension.  temp1 is a 16 bit unsigned number.  I am then performing logic AND with FFF to mask the first four upper most bits.  Then I am going to check to see if the upper most bit is  a one.  If it is then i am going to subtract 4096 from this number. 

If someone could send me a snippet of code that could implement this line, it would be greatly appreciated.

[dthor]

Is there some reason why you can't just cast the number to a different representation? Or am I misunderstanding the question?

[nathand]

Let me see if I understand correctly: you have a 12-bit signed value, stored in a 16-bit value, and you want it sign-extended through 16 bits?  I think there are easier ways to do this in both LabVIEW and C.  Here's one idea:

[GuenterMueller]

I think you are right with the 12bit assumption and your solution.

However, I would prefer the numeric way and thus avoid the BD constants.

[nathand]

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@GuenterMueller wrote:

I think you are right with the 12bit assumption and your solution.

However, I would prefer the numeric way and thus avoid the BD constants.

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Your method does not produce the right result.  A decimal value of 4095 (-1 for a 12-bit value, 0xFFF) correctly returns -1 in my code, but returns -4095 in yours.

[Matt_W1]

It's straight forward using shifts. This gives a different output if the input is beyond 12 bits though.

[GuenterMueller]

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@nathand wrote:

Your method does not produce the right result.  [...]

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Thanks. Your are right. My approach does not consider that the numbers still are ordered in a ring.