Union

联合类型的语法：

typedef union packed{struct packed{logic zero;logic [31:0]aluout;} alu;struct packed{logic zero;logic [31:0] pcbranch;}branch;struct packed {logic [31:0] addr;logic mem_read;}memory;
} result_t;result_t res;logic [31:0]addr, aluout;
assign addr = res.memory.addr; //assign addr = res[32:1]
assign aluout = res.alu.aluout;//assign aluout = res[31:0]

对union类型的变量进行赋值时，要注意多驱动
‘0是位全0，'1是位全1