Standard log2 function for integers

[shaiko]

Hello,

I know that the log2 function of the math_real package works on type "real".
Is there a standard VHDL function that calculates log2 for integers?

 

[TrickyDicky]

No. But I think its one of the first functions most engineers add to their toolbox.

 

[shaiko]

I know. I have one myself...just a general question.

1. Can I cast a "positive" type into a real type in order to apply the log2 ?
2. If #1 is possible, can I recast the result back to a "positive" after applying the log2 function?

 

[TrickyDicky]

1. Yes, but I dont know what it would do if you tried to synthesise it into a non constant location (like assigning a signal), or slicing a signal.
2. Yes, but remember that casting a real to an integer will round the result.

 

[shaiko]

1. Yes, but I dont know what it would do if you tried to synthesise it into a non constant location (like assigning a signal), or slicing a signal.

You mean during runtime operation as part of my RTL (not compile time) ?

 

[TrickyDicky]

Yes, runtime operations using real types are not allowed for synthesis.