Handle string[x] in l-values and system function arguments

When string[x] is an l-value, generate code to implement something
like the string.putc(x, ...) method.

Also handle when string[x] is the argument of a system task. In that
case resort to treating it as a calculated 8-bit vector, because that
is what it is.

elab_lval.cc

@@ -413,6 +413,22 @@ bool PEIdent::elaborate_lval_net_bit_(Design*des,
 		  lv->set_part(mux, lwid);
 	    }
 
+      } else if (reg->data_type() == IVL_VT_STRING) {
+	      // Special case: This is a select of a string
+	      // variable. The target of the assignment is a character
+	      // select of a string. Force the r-value to be an 8bit
+	      // vector and set the "part" to be the character select
+	      // expression. The code generator knows what to do with
+	      // this.
+	    if (debug_elaborate) {
+		  cerr << get_fileline() << ": debug: "
+		       << "Bit select of string becomes character select." << endl;
+	    }
+	    if (mux)
+		  lv->set_part(mux, 8);
+	    else
+		  lv->set_part(new NetEConst(verinum(lsb)), 8);
+
       } else if (mux) {
 	      // Non-constant bit mux. Correct the mux for the range
 	      // of the vector, then set the l-value part select

tgt-stub/expression.c

@@ -176,7 +176,9 @@ static void show_select_expression(ivl_expr_t net, unsigned ind)
 	      /* If the sub-expression is a STRING, then this is a
 		 substring and the code generator will handle it
 		 differently. */
-	    fprintf(out, "%*s<substring: width=%u/8>\n", ind, "", width);
+	    fprintf(out, "%*s<substring: width=%u bits, %u bytes>\n", ind, "", width, width/8);
+	    if (width%8 != 0)
+		  fprintf(out, "%*sERROR: Width should be a multiple of 8 bits.\n", ind, "", width);
 	    show_expression(oper1, ind+3);
 	    show_expression(oper2, ind+3);
 

tgt-vvp/draw_vpi.c

@@ -181,6 +181,12 @@ static int get_vpi_taskfunc_signal_arg(struct args_info *result,
 	    if (ivl_expr_type(vexpr) != IVL_EX_SIGNAL &&
 	        ivl_expr_type(vexpr) != IVL_EX_SELECT) return 0;
 
+	      /* If the expression is a substring expression, then
+		 the xPV method of passing the argument will not work
+		 and we have to resort to the default method. */
+	    if (ivl_expr_value(vexpr) == IVL_VT_STRING)
+		  return 0;
+
 	      /* The signal is part of an array. */
 	      /* Add &APV<> code here when it is finished. */
 	    bexpr = ivl_expr_oper2(expr);

tgt-vvp/stmt_assign.c

@@ -735,15 +735,34 @@ static int show_stmt_assign_sig_string(ivl_statement_t net)
 {
       ivl_lval_t lval = ivl_stmt_lval(net, 0);
       ivl_expr_t rval = ivl_stmt_rval(net);
-      ivl_signal_t var;
+      ivl_expr_t part = ivl_lval_part_off(lval);
+      ivl_signal_t var= ivl_lval_sig(lval);
+
       assert(ivl_stmt_lvals(net) == 1);
       assert(ivl_stmt_opcode(net) == 0);
+      assert(ivl_lval_mux(lval) == 0);
 
-      var = ivl_lval_sig(lval);
+	/* Simplest case: no mux. Evaluate the r-value as a string and
+	   store the result into the variable. Note that the
+	   %store/str opcode pops the string result. */
+      if (part == 0) {
+	    draw_eval_string(rval);
+	    fprintf(vvp_out, "    %%store/str v%p_0;\n", var);
+	    return 0;
+      }
 
-      draw_eval_string(rval);
-      fprintf(vvp_out, "    %%store/str v%p_0;\n", var);
+	/* Calculate the character select for the word. */
+      int mux_word = allocate_word();
+      draw_eval_expr_into_integer(part, mux_word);
 
+	/* Evaluate the r-value as a vector. */
+      struct vector_info rvec = draw_eval_expr_wid(rval, 8, STUFF_OK_XZ);
+
+      assert(rvec.wid == 8);
+      fprintf(vvp_out, "    %%putc/str/v v%p_0, %d, %u;\n", var, mux_word, rvec.base);
+
+      clr_vector(rvec);
+      clr_word(mux_word);
       return 0;
 }
 

vvp/codes.h

@@ -155,6 +155,7 @@ extern bool of_POW_S(vthread_t thr, vvp_code_t code);
 extern bool of_POW_WR(vthread_t thr, vvp_code_t code);
 extern bool of_PUSHI_STR(vthread_t thr, vvp_code_t code);
 extern bool of_PUSHV_STR(vthread_t thr, vvp_code_t code);
+extern bool of_PUTC_STR_V(vthread_t thr, vvp_code_t code);
 extern bool of_RELEASE_NET(vthread_t thr, vvp_code_t code);
 extern bool of_RELEASE_REG(vthread_t thr, vvp_code_t code);
 extern bool of_RELEASE_WR(vthread_t thr, vvp_code_t code);

vvp/compile.cc

@@ -203,6 +203,7 @@ static const struct opcode_table_s opcode_table[] = {
       { "%pow/wr", of_POW_WR, 2,  {OA_BIT1,     OA_BIT2,     OA_NONE} },
       { "%pushi/str",of_PUSHI_STR,1,{OA_STRING, OA_NONE,     OA_NONE} },
       { "%pushv/str", of_PUSHV_STR, 2, {OA_BIT1,OA_BIT2,     OA_NONE} },
+      { "%putc/str/v",of_PUTC_STR_V,3,{OA_FUNC_PTR,OA_BIT1,  OA_BIT2} },
       { "%release/net",of_RELEASE_NET,3,{OA_FUNC_PTR,OA_BIT1,OA_BIT2} },
       { "%release/reg",of_RELEASE_REG,3,{OA_FUNC_PTR,OA_BIT1,OA_BIT2} },
       { "%release/wr",of_RELEASE_WR,2,{OA_FUNC_PTR,OA_BIT1,OA_NONE} },

vvp/vthread.cc

@@ -4279,6 +4279,55 @@ bool of_PUSHV_STR(vthread_t thr, vvp_code_t cp)
       return true;
 }
 
+/*
+ * %putc/str/v  <var>, <muxr>, <base>
+ */
+bool of_PUTC_STR_V(vthread_t thr, vvp_code_t cp)
+{
+      unsigned muxr = cp->bit_idx[0];
+      unsigned base = cp->bit_idx[1];
+
+	/* The mux is the index into the string. If it is <0, then
+	   this operation cannot possible effect the string, so we are
+	   done. */
+      assert(muxr < 16);
+      int32_t mux = thr->words[muxr].w_int;
+      if (mux < 0)
+	    return true;
+
+	/* Extract the character from the vector space. If that byte
+	   is null (8'hh00) then there is nothing more to do. */
+      unsigned long*tmp = vector_to_array(thr, base, 8);
+      if (tmp == 0)
+	    return true;
+      if (tmp[0] == 0)
+	    return true;
+
+      char tmp_val = tmp[0]&0xff;
+
+	/* Get the existing value of the string. If we find that the
+	   index is too big for the string, then give up. */
+      vvp_net_t*net = cp->net;
+      vvp_fun_signal_string*fun = dynamic_cast<vvp_fun_signal_string*> (net->fun);
+      assert(fun);
+
+      string val = fun->get_string();
+      if (val.size() <= (size_t)mux)
+	    return true;
+
+	/* If the value to write is the same as the destination, then
+	   stop now. */
+      if (val[mux] == tmp_val)
+	    return true;
+
+	/* Finally, modify the string and write the new string to the
+	   variable so that the new value propagates. */
+      val[mux] = tmp_val;
+      vvp_send_string(vvp_net_ptr_t(cp->net, 0), val, thr->wt_context);
+
+      return true;
+}
+
 /*
  * These implement the %release/net and %release/reg instructions. The
  * %release/net instruction applies to a net kind of functor by