Fix casting reals to large integrals (#6085)

src/V3Width.cpp

@@ -2168,7 +2168,7 @@ class WidthVisitor final : public VNVisitor {
             // Note we don't sign fromp() that would make the algorithm O(n^2) if lots of casting.
             AstNodeExpr* newp = nullptr;
             if (bad) {
-            } else if (const AstBasicDType* const basicp = toDtp->basicp()) {
+            } else if (AstBasicDType* const basicp = toDtp->basicp()) {
                 if (!basicp->isString() && fromDtp->isString()) {
                     newp = new AstNToI{nodep->fileline(), nodep->fromp()->unlinkFrBack(), toDtp};
                 } else if (!basicp->isDouble() && !fromDtp->isDouble()) {
@@ -2192,7 +2192,7 @@ class WidthVisitor final : public VNVisitor {
                     }
                 } else if (!basicp->isDouble() && nodep->fromp()->isDouble()) {
                     newp = new AstRToIRoundS{nodep->fileline(), nodep->fromp()->unlinkFrBack()};
-                    newp->dtypeChgSigned(basicp->isSigned());
+                    newp->dtypep(basicp);
                 } else if (basicp->isSigned() && !nodep->fromp()->isSigned()) {
                     newp = new AstSigned{nodep->fileline(), nodep->fromp()->unlinkFrBack()};
                 } else if (!basicp->isSigned() && nodep->fromp()->isSigned()) {

test_regress/t/t_real_cast.py

@@ -0,0 +1,18 @@
+#!/usr/bin/env python3
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2024 by Wilson Snyder. This program is free software; you
+# can redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+import vltest_bootstrap
+
+test.scenarios("vlt")
+
+test.compile()
+
+test.execute()
+
+test.passes()

test_regress/t/t_real_cast.v

@@ -0,0 +1,39 @@
+// DESCRIPTION: Verilator: Confirm x randomization stability
+//
+// This file ONLY is placed under the Creative Commons Public Domain, for
+// any use, without warranty, 2025 by Wilson Snyder.
+// SPDX-License-Identifier: CC0-1.0
+
+module t (/*AUTOARG*/
+    // Inputs
+    clk
+    );
+
+    input clk;
+
+    typedef logic [85:0] big_t;
+    localparam big_t foo = big_t'(8.531630271583128e+16);
+
+    big_t bar;
+    int cyc;
+    real some_real;
+
+    initial begin
+        cyc = 0;
+        some_real = 5.123;
+    end
+
+    always_comb bar = big_t'(some_real);
+
+    always @(posedge clk) begin
+        cyc <= cyc + 1;
+        some_real <= some_real * 1.234e4;
+        if (cyc == 6) begin
+            if (foo != 86'd85316302715831280) $stop();
+            if (bar != 86'd18089031459271914704338944) $stop();
+            $write("*-* All Finished *-*\n");
+            $finish;
+        end
+    end
+
+endmodule