[flang-commits] [PATCH] D127428: [flang][runtime] Detect overflow of fixed-sized exponent output field

[Peter Klausler via Phabricator via flang-commits]

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When Ew.dEe or Gw.dEe output has an exponent requiring more than 'e'
digits, the whole output field must overflow to asterisks.  The runtime
was detecting short fields and padding them with zeroes, but not
overflow.


https://reviews.llvm.org/D127428

Files:
  flang/runtime/edit-output.cpp
  flang/runtime/edit-output.h


Index: flang/runtime/edit-output.h
===================================================================
--- flang/runtime/edit-output.h
+++ flang/runtime/edit-output.h
@@ -52,6 +52,7 @@
     return *p < '0' || *p > '9';
   }
 
+  // Returns null when the exponent overflows a fixed-size output field.
   const char *FormatExponent(int, const DataEdit &edit, int &length);
   bool EmitPrefix(const DataEdit &, std::size_t length, std::size_t width);
   bool EmitSuffix(const DataEdit &);
Index: flang/runtime/edit-output.cpp
===================================================================
--- flang/runtime/edit-output.cpp
+++ flang/runtime/edit-output.cpp
@@ -182,8 +182,10 @@
     *--exponent = '0' + e - 10 * quotient;
     e = quotient;
   }
+  bool overflow{false};
   if (edit.expoDigits) {
     if (int ed{*edit.expoDigits}) { // Ew.dEe with e > 0
+      overflow = exponent + ed < eEnd;
       while (exponent > exponent_ + 2 /*E+*/ && exponent + ed > eEnd) {
         *--exponent = '0';
       }
@@ -200,7 +202,7 @@
     *--exponent = edit.descriptor == 'D' ? 'D' : 'E'; // not 'G'
   }
   length = eEnd - exponent;
-  return exponent;
+  return overflow ? nullptr : exponent;
 }
 
 bool RealOutputEditingBase::EmitPrefix(
@@ -352,7 +354,7 @@
         1 /*'.'*/ + zeroesAfterPoint + digitsAfterPoint + trailingZeroes +
         expoLength};
     int width{editWidth > 0 ? editWidth : totalLength};
-    if (totalLength > width) {
+    if (totalLength > width || !exponent) {
       return io_.EmitRepeated('*', width);
     }
     if (totalLength < width && digitsBeforePoint == 0 &&


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