[flang][runtime] Fix fixed-width field internal wide character input

[klausler]

There was some confusion about units (bytes vs characters) in the handling of the amount of input remaining in fixed-width formatted input fields. Clarify that any variable or parameter counting "remaining" space in a field in the I/O runtime is always in units of bytes, and make it so where it wasn't.

Fixes the bug(s) in llvm-test-suite/Fortran/gfortran/regression/char4_iunit_2.f03, although the test still won't pass due to its dependence on gfortran's list-directed output spacing.

[llvmbot]

@llvm/pr-subscribers-flang-runtime

Author: Peter Klausler (klausler)

Changes

There was some confusion about units (bytes vs characters) in the handling of the amount of input remaining in fixed-width formatted input fields. Clarify that any variable or parameter counting "remaining" space in a field in the I/O runtime is always in units of bytes, and make it so where it wasn't.

Fixes the bug(s) in llvm-test-suite/Fortran/gfortran/regression/char4_iunit_2.f03, although the test still won't pass due to its dependence on gfortran's list-directed output spacing.

---

Full diff: https://github.com/llvm/llvm-project/pull/74683.diff

2 Files Affected:

• (modified) flang/runtime/edit-input.cpp (+10-9)
• (modified) flang/runtime/io-stmt.h (+11-3)

diff --git a/flang/runtime/edit-input.cpp b/flang/runtime/edit-input.cpp
index 4e8c9aa868a69..9dcca5bea6d93 100644
--- a/flang/runtime/edit-input.cpp
+++ b/flang/runtime/edit-input.cpp
@@ -915,18 +915,22 @@ bool EditCharacterInput(
     return false;
   }
   const ConnectionState &connection{io.GetConnectionState()};
-  std::size_t remaining{length};
+  int unitBytesPerChar{std::max<int>(connection.internalIoCharKind, 1)};
+  std::size_t remaining{length * unitBytesPerChar};
+  // Skip leading characters.
+  // Their bytes don't count towards INQUIRE(IOLENGTH=).
+  std::size_t skip{0};
   if (edit.width && *edit.width > 0) {
-    remaining = *edit.width;
+    remaining = *edit.width * unitBytesPerChar;
+    if (static_cast<std::size_t>(*edit.width) > length) {
+      skip = *edit.width - length;
+    }
   }
   // When the field is wider than the variable, we drop the leading
   // characters.  When the variable is wider than the field, there can be
   // trailing padding or an EOR condition.
   const char *input{nullptr};
   std::size_t ready{0};
-  // Skip leading bytes.
-  // These bytes don't count towards INQUIRE(IOLENGTH=).
-  std::size_t skip{remaining > length ? remaining - length : 0};
   // Transfer payload bytes; these do count.
   while (remaining > 0) {
     if (ready == 0) {
@@ -958,7 +962,6 @@ bool EditCharacterInput(
         // error recovery: skip bad encoding
         chunk = 1;
       }
-      --remaining;
     } else if (connection.internalIoCharKind > 1) {
       // Reading from non-default character internal unit
       chunk = connection.internalIoCharKind;
@@ -970,7 +973,6 @@ bool EditCharacterInput(
         *x++ = buffer;
         --length;
       }
-      --remaining;
     } else if constexpr (sizeof *x > 1) {
       // Read single byte with expansion into multi-byte CHARACTER
       chunk = 1;
@@ -980,7 +982,6 @@ bool EditCharacterInput(
         *x++ = static_cast<unsigned char>(*input);
         --length;
       }
-      --remaining;
     } else { // single bytes -> default CHARACTER
       if (skipping) {
         chunk = std::min<std::size_t>(skip, ready);
@@ -991,9 +992,9 @@ bool EditCharacterInput(
         x += chunk;
         length -= chunk;
       }
-      remaining -= chunk;
     }
     input += chunk;
+    remaining -= chunk;
     if (!skipping) {
       io.GotChar(chunk);
     }
diff --git a/flang/runtime/io-stmt.h b/flang/runtime/io-stmt.h
index d4ceb83265246..91169f6c6e323 100644
--- a/flang/runtime/io-stmt.h
+++ b/flang/runtime/io-stmt.h
@@ -92,8 +92,8 @@ class IoStatementState {
   std::size_t GetNextInputBytes(const char *&);
   bool AdvanceRecord(int = 1);
   void BackspaceRecord();
-  void HandleRelativePosition(std::int64_t);
-  void HandleAbsolutePosition(std::int64_t); // for r* in list I/O
+  void HandleRelativePosition(std::int64_t byteOffset);
+  void HandleAbsolutePosition(std::int64_t byteOffset); // for r* in list I/O
   std::optional<DataEdit> GetNextDataEdit(int maxRepeat = 1);
   ExternalFileUnit *GetExternalFileUnit() const; // null if internal unit
   bool BeginReadingRecord();
@@ -124,7 +124,11 @@ class IoStatementState {
   // Vacant after the end of the current record
   std::optional<char32_t> GetCurrentChar(std::size_t &byteCount);
 
-  // For fixed-width fields, return the number of remaining characters.
+  // The "remaining" arguments to CueUpInput(), SkipSpaces(), & NextInField()
+  // are always in units of bytes, not characters; the distinction matters
+  // for internal input from CHARACTER(KIND=2 and 4).
+
+  // For fixed-width fields, return the number of remaining bytes.
   // Skip over leading blanks.
   std::optional<int> CueUpInput(const DataEdit &edit) {
     std::optional<int> remaining;
@@ -134,6 +138,10 @@ class IoStatementState {
     } else {
       if (edit.width.value_or(0) > 0) {
         remaining = *edit.width;
+        if (int bytesPerChar{GetConnectionState().internalIoCharKind};
+            bytesPerChar > 1) {
+          *remaining *= bytesPerChar;
+        }
       }
       SkipSpaces(remaining);
     }

[clementval]

LGTM