1. A calculation circuit for calculating logical fuzzy union and intersection operations, comprising: subtracter means having a first and a second input receiving a first and, respectively, a second input datum; a first output supplying a first output datum correlated to the difference between said first and second input datum; and a second output supplying a sign flag indicating the sign of said first output datum; comparison means having a first input receiving said sign flag, a second input receiving a first selection signal assuming a first level for the selection of said logical fuzzy union operation and a second level for the selection of said logical fuzzy intersection operation; and an output supplying a second selection signal assuming a first level when said sign flag and said first selection signal comply with a pre-determined relation and a second level when said sign flag and said first selection signal do not comply with said pre-determined relation; and first data selection means having a first and a second datum input receiving said first and, respectively, said second input datum; a selection input connected to said output of said comparison means and receiving said second selection signal; and an output supplying a second output datum correlated to one of said first and second input data as a function of the level of said second selection signal.