RE: [sv-bc] Agenda: January 21, 2008 SV-BC Meeting (NOTE: NEW CALL LOGISTICS)

The verbiage of the $clog2 function is contradictory and misleading.

 

The first paragraph containing the formal definition of the function and
the second paragraph are contradictory:

 

The system function $clog2 shall return the ceiling of the log base 2 of
the argument (the log rounded up to

an integer value). The argument can be an integer or an arbitrary sized
vector value. The argument shall be

treated as an unsigned value, and an argument value of 0 shall produce a
result of 0.

 

This system function can be used to compute the minimum address width
necessary to address a memory of

a given size or the minimum vector width necessary to represent a given
number of states.

 

For example:

 

integer result;

result = $clog2(n);

 

The second paragraph has led some users to believe that $clog2 returns
the minimum number of bits needed to store a particular value, but, that
is not true if $clog2 is indeed ceil( log2( N ) ). The general
expression needed to determine the minimum number of bits would be
$clog2(N | 1) not  $clog2(N). The example seems to reinforce this idea.
The second paragraph's intent seems to be informational only, that is,
the $clog2 function can be used *as an aid* to compute the minimum
vector width.

 

            Arturo

 


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