位向量系统函数

1 基本概念

$countbits ( expression , list_of_control_bits )

$countones ( expression )

$onehot ( expression )

$onehot0 ( expression )

$isunknown ( expression )

2 示例

1 $countbits

        The function $countbits counts the number of bits that have a specific set of values (e.g., 0, 1, X, Z) in a

        This function returns an int equal to the number of bits in expression whose values match one of the control_bit entries. For example:

        — $countbits (expression, '1) returns the number of bits in expression having value 1.

        — $countbits (expression, '1, '0) returns the number of bits in expression having values

1 or 0.

        — $countbits (expression, 'x, 'z) returns the number of bits in expression having values X

or Z.

2 $countones

$countones ( expression ) is equivalent to $countbits(expression,'1). 

3 $onehot

— $onehot ( expression ) returns true (1'b1) if $countbits(expression,'1)==1, otherwise it

returns false (1'b0). 

4 $onehot

— $onehot0 ( expression ) returns true (1'b1) if $countbits(expression,'1)<=1, otherwise it

returns false (1'b0). 

5 $isunknown

$isunknown ( expression ) returns true (1'b1) if $countbits(expression,'x,'z)!=0,

otherwise it returns false (1'b0). 

3 应用