Implement arithmetic right shift >>>

This is currently implemented using the numeric_std
shift_right function as the sra operator is not defined on
signed/unsigned types before VHDL-2006.

tgt-vhdl/expr.cc

@@ -241,7 +241,20 @@ static vhdl_expr *translate_shift(vhdl_expr *lhs, vhdl_expr *rhs,
    vhdl_expr *r_cast = rhs->cast(&integer);
 
    vhdl_type *rtype = new vhdl_type(*lhs->get_type());
-   return new vhdl_binop_expr(lhs, op, r_cast, rtype);
+
+   // The sra operator is not defined on numeric_std types until
+   // VHDL-2006 which is not well supported. Instead we can use
+   // the shift_right function which does the same thing and
+   // exists in earlier versions of numeric_std.
+   if (op == VHDL_BINOP_SRA) {
+      vhdl_fcall *sra = new vhdl_fcall("shift_right", rtype);
+      sra->add_expr(lhs);
+      sra->add_expr(r_cast);
+
+      return sra;
+   }
+   else
+      return new vhdl_binop_expr(lhs, op, r_cast, rtype);
 }
 
 /*
@@ -388,6 +401,15 @@ static vhdl_expr *translate_binary(ivl_expr_t e)
    case 'r':
       result = translate_shift(lhs, rhs, VHDL_BINOP_SR);
       break;
+   case 'R':    // Arithmetic right shift
+      // Verilog only actually performs a signed shift if the
+      // argument being shifted is signed, otherwise it defaults
+      // to a normal shift
+      if (ivl_expr_signed(ivl_expr_oper1(e)))
+         result = translate_shift(lhs, rhs, VHDL_BINOP_SRA);
+      else
+         result = translate_shift(lhs, rhs, VHDL_BINOP_SR);
+      break;         
    case '^':
       result = translate_numeric(lhs, rhs, VHDL_BINOP_XOR);
       break;

tgt-vhdl/vhdl_syntax.cc

@@ -730,7 +730,7 @@ void vhdl_binop_expr::emit(std::ostream &of, int level) const
       const char* ops[] = {
          "and", "or", "=", "/=", "+", "-", "*", "<",
          ">", "<=", ">=", "sll", "srl", "xor", "&",
-         "nand", "nor", "xnor", "/", "mod", "**", NULL
+         "nand", "nor", "xnor", "/", "mod", "**", "sra", NULL
       };
 
       of << " " << ops[op_] << " ";

tgt-vhdl/vhdl_syntax.hh

@@ -92,6 +92,7 @@ enum vhdl_binop_t {
    VHDL_BINOP_DIV,
    VHDL_BINOP_MOD,
    VHDL_BINOP_POWER,
+   VHDL_BINOP_SRA,
 };
 
 /*