[flang] Respect BZ mode in exponent parts, too

[klausler]

Summary

The Fortran standard discusses BZ mode (treat blanks as zero digits)
explicitly in its effect on the editing of the digits prior to the
exponent part, but doesn't mention it in description of the
exponent part. Other compilers honor BZ mode in the exponent,
so we should do so too. So "1 e 1 " is 1.E11 in BZ mode.

flang/runtime/edit-input.cpp

if (next && *next == '(') { // NaN(...)
         next = io.NextInField(remaining);
       }
     }
     exponent = 0;
   } else if (first == decimal || (first >= '0' && first <= '9') ||
       first == 'E' || first == 'D' || first == 'Q') {
     Put('.'); // input field is normalized to a fraction
     auto start{got};
+    bool bzMode{(edit.modes.editingFlags & blankZero) != 0};
     for (; next; next = io.NextInField(remaining)) {
       char32_t ch{*next};
       if (ch == ' ' || ch == '\t') {
-        if (edit.modes.editingFlags & blankZero) {
+        if (bzMode) {
           ch = '0'; // BZ mode - treat blank as if it were zero
         } else {
           continue;
         }
       }
       if (ch == '0' && got == start && !decimalPoint) {
         // omit leading zeroes before the decimal
       } else if (ch >= '0' && ch <= '9') {
         Put(ch);
       } else if (ch == decimal && !decimalPoint) {
         // the decimal point is *not* copied to the buffer
         decimalPoint = got - start; // # of digits before the decimal point
       } else {
         break;
       }
     }
     if (got == start) {
       Put('0'); // emit at least one digit
     }
     if (next &&
         (*next == 'e' || *next == 'E' || *next == 'd' || *next == 'D' ||
             *next == 'q' || *next == 'Q')) {
+      // Optional exponent letter.  Blanks are allowed between the
+      // optional exponent letter and the exponent value.
       io.SkipSpaces(remaining);
       next = io.NextInField(remaining);
     }
-    exponent = -edit.modes.scale; // default exponent is -kP
+    // The default exponent is -kP, but the scale factor doesn't affect
+    // an explicit exponent.
+    exponent = -edit.modes.scale;
     if (next &&
-        (*next == '-' || *next == '+' || (*next >= '0' && *next <= '9'))) {
+        (*next == '-' || *next == '+' || (*next >= '0' && *next <= '9') ||
+            (bzMode && (*next == ' ' || *next == '\t')))) {
       bool negExpo{*next == '-'};
       if (negExpo || *next == '+') {
         next = io.NextInField(remaining);
       }
-      for (exponent = 0; next && (*next >= '0' && *next <= '9');
-           next = io.NextInField(remaining)) {
+      for (exponent = 0; next; next = io.NextInField(remaining)) {
+        if (*next >= '0' && *next <= '9') {
           exponent = 10 * exponent + *next - '0';
+        } else if (bzMode && (*next == ' ' || *next == '\t')) {
+          exponent = 10 * exponent;
+        } else {
+          break;
+        }
       }
       if (negExpo) {
         exponent = -exponent;
       }
     }
     if (decimalPoint) {
       exponent += *decimalPoint;
     } else {

flang/unittests/Runtime/hello.cpp

int main() {
   realInTest("(F18.0)", "            0.0625", 0x3fb0000000000000);
   realInTest("(F18.0)", "               125", 0x405f400000000000);
   realInTest("(F18.1)", "               125", 0x4029000000000000);
   realInTest("(F18.2)", "               125", 0x3ff4000000000000);
   realInTest("(F18.3)", "               125", 0x3fc0000000000000);
   realInTest("(-1P,F18.0)", "               125", 0x4093880000000000); // 1250
   realInTest("(1P,F18.0)", "               125", 0x4029000000000000); // 12.5
   realInTest("(BZ,F18.0)", "              125 ", 0x4093880000000000); // 1250
+  realInTest("(BZ,F18.0)", "       125 . e +1 ", 0x42a6bcc41e900000); // 1.25e13
   realInTest("(DC,F18.0)", "              12,5", 0x4029000000000000);
 
   listInputTest();
 
   return EndTests();
 }