[flang-commits] [flang] [flang][runtime] Fix off-by-one error in EX0.0 output editing (PR #85428)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-flang-runtime

Author: Peter Klausler (klausler)

<details>
<summary>Changes</summary>

The maximum number of significant hexadecimal digits in EX0.0 REAL output editing is 29, not 28.  Fix by computing it at build time from the precision of REAL(16).

---
Full diff: https://github.com/llvm/llvm-project/pull/85428.diff


1 Files Affected:

- (modified) flang/runtime/edit-output.cpp (+4-1) 


``````````diff
diff --git a/flang/runtime/edit-output.cpp b/flang/runtime/edit-output.cpp
index b474c8cd91bae4..7267540370fc07 100644
--- a/flang/runtime/edit-output.cpp
+++ b/flang/runtime/edit-output.cpp
@@ -9,6 +9,7 @@
 #include "edit-output.h"
 #include "emit-encoded.h"
 #include "utf.h"
+#include "flang/Common/real.h"
 #include "flang/Common/uint128.h"
 #include <algorithm>
 
@@ -700,7 +701,9 @@ bool RealOutputEditing<KIND>::EditEXOutput(const DataEdit &edit) {
   if ((editWidth == 0 && !edit.digits) || editDigits == 0) {
     // EX0 or EXw.0
     flags |= decimal::Minimize;
-    significantDigits = 28; // enough for 128-bit F.P.
+    static constexpr int maxSigHexDigits{
+        (common::PrecisionOfRealKind(16) + 3) / 4};
+    significantDigits = maxSigHexDigits;
   }
   auto converted{
       ConvertToHexadecimal(significantDigits, edit.modes.round, flags)};

``````````

</details>


https://github.com/llvm/llvm-project/pull/85428