Merged revision(s) 20564 from trunk/OpenMPT:

[Imp] M15: The heuristics in r20524 were still too loose, also identifying completely unrelated file types. We validate the pattern data much more thoroughly now and check that there are no weird period values. There's one extremely damaged M15 file that will no longer play, but it was not particularly listenable before this change (even sample length were incorrect, lots of pattern garbage, etc.), so it's no big loss.
........


git-svn-id: https://source.openmpt.org/svn/openmpt/branches/OpenMPT-1.30@20566 56274372-70c3-4bfc-bfc3-4c3a0b034d27

soundlib/Load_mod.cpp

@@ -534,16 +534,28 @@ static uint32 ReadSample(FileReader &file, MODSampleHeader &sampleHeader, ModSam
 
 
 // Count malformed bytes in MOD pattern data
-static uint32 CountMalformedMODPatternData(const MODPatternData &patternData, const bool allow31Samples)
+static uint32 CountMalformedMODPatternData(const MODPatternData &patternData, const bool extendedFormat)
 {
- const uint8 mask = allow31Samples ? 0xE0 : 0xF0;
+ const uint8 mask = extendedFormat ? 0xE0 : 0xF0;
  uint32 malformedBytes = 0;
  for(const auto &row : patternData)
  {
  for(const auto &data : row)
  {
  if(data[0] & mask)
  malformedBytes++;
+ if(!extendedFormat)
+ {
+ const uint16 period = (((static_cast<uint16>(data[0]) & 0x0F) << 8) | data[1]);
+ if(period && period != 0xFFF)
+ {
+ // Allow periods to deviate by +/-1 as found in some files
+ const auto CompareFunc = [](uint16 l, uint16 r) { return l > (r + 1); };
+ const auto PeriodTable = mpt::as_span(ProTrackerPeriodTable).subspan(24, 36);
+ if(!std::binary_search(PeriodTable.begin(), PeriodTable.end(), period, CompareFunc))
+ malformedBytes += 2;
+ }
+ }
  }
  }
  return malformedBytes;
@@ -552,12 +564,12 @@ static uint32 CountMalformedMODPatternData(const MODPatternData &patternData, co
 
 // Check if number of malformed bytes in MOD pattern data exceeds some threshold
 template <typename TFileReader>
-static bool ValidateMODPatternData(TFileReader &file, const uint32 threshold, const bool allow31Samples)
+static bool ValidateMODPatternData(TFileReader &file, const uint32 threshold, const bool extendedFormat)
 {
  MODPatternData patternData;
  if(!file.Read(patternData))
  return false;
- return CountMalformedMODPatternData(patternData, allow31Samples) <= threshold;
+ return CountMalformedMODPatternData(patternData, extendedFormat) <= threshold;
 }
 
 
@@ -1614,7 +1626,7 @@ bool CSoundFile::ReadM15(FileReader &file, ModLoadingFlags loadFlags)
  // "operation wolf" soundtrack have 15 patterns for several songs, but the last few patterns are just garbage.
  // Apart from those hidden patterns, the files play fine.
  // Example: operation wolf - wolf1.mod (MD5 739acdbdacd247fbefcac7bc2d8abe6b, SHA1 e6b4813daacbf95f41ce9ec3b22520a2ae07eed8)
- if(illegalBytes > 512)
+ if(illegalBytes > std::max(512u, numPatterns * 128u))
  return false;
  }
  for(ROWINDEX row = 0; row < 64; row++)