#12 (1.6.0) Attribution to fields in formatted regs

ArchC 1.6.0.

A formatted register is a class with the following
declaration:

class ac_RRR {
char* name;
public:
ac_reg<unsigned> field1;
ac_reg<unsigned> field2;

ac_LL(char* n):
lladdr("LL",0),
llbit("LL",0){name = n;}

void change_dump(ostream& output){}

void reset_log(){}

void behavior(ac_stage_list stage = (ac_stage_list)0,
int cycle = 0);

void commit_delays(double dummy) {}
};

Let X be an unsigned integer, let field1 be the
rightmost k-bit field in register RRR and consider that
X has some residue in the (wordsize - k)-leftmost part.
An attribution such as RRR.field1 = X does not clear
the wordsize - k leftmost bits of RRR.field1.
Consequently, if RRR.field1 is used without masking its
k bits, the leftmost bits inherited from X might
influence the result of operations on RRR.field1.