[flang][runtime] Improve G0 output editing

G0 output editing should never overflow an output field and fill it
with asterisks.  It should also never elide the "E" in an exponent
field, even if it has more than three digits.

Differential Revision: https://reviews.llvm.org/D128396

Author: klausler

flang/runtime/edit-output.cpp

@@ -199,7 +199,7 @@ const char *RealOutputEditingBase::FormatExponent(
   }
   *--exponent = expo < 0 ? '-' : '+';
   if (edit.expoDigits || edit.IsListDirected() || exponent + 3 == eEnd) {
-    *--exponent = edit.descriptor == 'D' ? 'D' : 'E'; // not 'G'
+    *--exponent = edit.descriptor == 'D' ? 'D' : 'E'; // not 'G' or 'Q'
   }
   length = eEnd - exponent;
   return overflow ? nullptr : exponent;
@@ -264,9 +264,7 @@ bool RealOutputEditing<binaryPrecision>::EditEorDOutput(const DataEdit &edit) {
   if (editWidth == 0) { // "the processor selects the field width"
     if (edit.digits.has_value()) { // E0.d
       if (editDigits == 0) { // E0.0
-        editWidth = 7; // -.0E+ee
-      } else {
-        editWidth = editDigits + 6; // -.666E+ee
+        significantDigits = 1;
       }
     } else { // E0
       flags |= decimal::Minimize;
@@ -485,7 +483,7 @@ DataEdit RealOutputEditing<binaryPrecision>::EditForGOutput(DataEdit edit) {
   int significantDigits{
       edit.digits.value_or(BinaryFloatingPoint::decimalPrecision)}; // 'd'
   if (editWidth > 0 && significantDigits == 0) {
-    return edit; // Gw.0 -> Ew.0 for w > 0
+    return edit; // Gw.0Ee -> Ew.0Ee for w > 0
   }
   int flags{0};
   if (edit.modes.editingFlags & signPlus) {
@@ -498,7 +496,10 @@ DataEdit RealOutputEditing<binaryPrecision>::EditForGOutput(DataEdit edit) {
   }
   int expo{IsZero() ? 1 : converted.decimalExponent}; // 's'
   if (expo < 0 || expo > significantDigits) {
-    return edit; // Ew.d
+    if (editWidth == 0 && !edit.expoDigits) { // G0.d -> G0.dE0
+      edit.expoDigits = 0;
+    }
+    return edit; // Ew.dEe
   }
   edit.descriptor = 'F';
   edit.modes.scale = 0; // kP is ignored for G when no exponent field

flang/unittests/Runtime/NumericalFormatTest.cpp

@@ -394,9 +394,9 @@ TEST(IOApiTests, FormatDoubleValues) {
               {"(E62.55,';')",
                   " 0.1000000000000000055511151231257827021181583404541015625E+"
                   "00;"},
-              {"(E0.0,';')", "0.E+00;"},
+              {"(E0.0,';')", ".1E+00;"},
               {"(E0.55,';')",
-                  "0.1000000000000000055511151231257827021181583404541015625E+"
+                  ".1000000000000000055511151231257827021181583404541015625E+"
                   "00;"},
               {"(E0,';')", ".1E+00;"},
               {"(F58.55,';')",
@@ -491,7 +491,7 @@ TEST(IOApiTests, FormatDoubleValues) {
                   "701797267771758512566055119913150489110145103786273816725095"
                   "583738973359899366480994116420570263709027924276754456522908"
                   "75386825064197182655334472656250-323;"},
-              {"(G0,';')", ".5-323;"},
+              {"(G0,';')", ".5E-323;"},
               {"(E757.750,';')",
                   " 0."
                   "494065645841246544176568792868221372365059802614324764425585"
@@ -586,7 +586,7 @@ TEST(IOApiTests, FormatDoubleValues) {
                   "408698898317506783884692609277397797285865965494109136909540"
                   "61364675687023986783152906809846172109246253967285156250-"
                   "307;"},
-              {"(G0,';')", ".22250738585072014-307;"},
+              {"(G0,';')", ".22250738585072014E-307;"},
           }},
       {// greatest finite
           0x7fefffffffffffffuLL,
@@ -616,7 +616,7 @@ TEST(IOApiTests, FormatDoubleValues) {
                   "090389328944075868508455133942304583236903222948165808559332"
                   "123348274797826204144723168738177180919299881250404026184124"
                   "8583680000+306;"},
-              {"(G0,';')", ".17976931348623157+309;"},
+              {"(G0,';')", ".17976931348623157E+309;"},
           }},
   };