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Forum: FPGA, VHDL & Verilog ceil and log2 functions


ceil and log2 functions
von Matt (Guest)

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I have the following line of code:

constant DPRAM_DEPTH : integer := integer(ceil(log2(real(NUM_SLOTS))));

When NUM_SLOTS equals 0, I want my DPRAM_WIDTH to be 0, however log2 of 
0 is negative infinity so I get an invalid result. How can I obtain 0 
when NUM_SLOTS is 0, and still get the functionality I want out of that 
snippet of code?

Thanks

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Re: ceil and log2 functions
von Markus F. (mfro)

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If you just need this to define a constant, you can do something like 
this:

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function log2ceil(m : integer) return integer is

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begin

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  for i in 0 to integer'high loop

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        if 2 ** i >= m then

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            return i;

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        end if;

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    end loop;

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end function log2ceil;

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constant x   : integer := log2ceil(16);


This way, it will not use up any logic during synthesis.

  


  




  

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