[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

       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 (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;

flang/unittests/Runtime/hello.cpp

   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();