Report REALCVT on $display format mistakes.

src/V3Width.cpp

@@ -2843,10 +2843,17 @@ private:
                 case 'm': break;  // %m - auto insert "name"
                 case 'l': break;  // %m - auto insert "library"
                 case 'd': {  // Convert decimal to either 'd' or '#'
-                    if (argp && argp->isSigned()) {  // Convert it
+                    if (argp) {
+                        AstNode* nextp = argp->nextp();
+                        if (argp->isDouble()) {
+                            spliceCvtS(argp, true, 64);
                             ch = '~';
                         }
-                    if (argp) argp = argp->nextp();
+                        else if (argp->isSigned()) {  // Convert it
+                            ch = '~';
+                        }
+                        argp = nextp;
+                    }
                     break;
                 }
                 case 'p': {  // Pattern
@@ -2895,6 +2902,17 @@ private:
                     if (argp) argp = argp->nextp();
                     break;
                 }
+                case 'f':  // FALLTHRU
+                case 'g': {
+                    if (argp) {
+                        AstNode* nextp = argp->nextp();
+                        if (!argp->isDouble()) {
+                            iterateCheckReal(nodep, "Display argument", argp, BOTH);
+                        }
+                        argp = nextp;
+                    }
+                    break;
+                }
                 case '?': {  // Unspecified by user, guess
                     if (argp && argp->isDouble()) {
                         ch = 'g';

test_regress/t/t_display.v

@@ -171,7 +171,9 @@ multiline", $time);
       $write("'%-8s'\n", "beep");
 
       // $itord conversion bug, note a %d instead of proper float
+      // verilator lint_off REALCVT
       $display("log10(2) = %d", $log10(100));
+      // verilator lint_on REALCVT
 
       $write("*-* All Finished *-*\n");
       $finish;