V649. There are two 'if' statements with identical conditional expressions. The first 'if' statement contains function return. This means that the second 'if' statement is senseless.

The analyzer has detected an issue when the 'then' part of the 'if' operator never gets control. It happens because there is another 'if' before which contains the same condition whose 'then' part contains the unconditional 'return' operator. It may signal both a logical error in the program and an unnecessary second 'if' operator.

Consider the following example of incorrect code:

if (l >= 0x06C0 && l <= 0x06CE) return true;
if (l >= 0x06D0 && l <= 0x06D3) return true;
if (l == 0x06D5) return true;                 <<<---
if (l >= 0x06E5 && l <= 0x06E6) return true;
if (l >= 0x0905 && l <= 0x0939) return true;
if (l == 0x06D5) return true;                 <<<---
if (l >= 0x0958 && l <= 0x0961) return true;
if (l >= 0x0985 && l <= 0x098C) return true;

In this case, the 'l == 0x06D5' condition is doubled, and we just need to remove one of them to fix the code. However, it may be that the value being checked in the second case should be different from the first one.

This is the fixed code:

if (l >= 0x06C0 && l <= 0x06CE) return true;
if (l >= 0x06D0 && l <= 0x06D3) return true;
if (l == 0x06D5) return true;
if (l >= 0x06E5 && l <= 0x06E6) return true;
if (l >= 0x0905 && l <= 0x0939) return true;
if (l >= 0x0958 && l <= 0x0961) return true;
if (l >= 0x0985 && l <= 0x098C) return true;

The V649 warning may indirectly point to errors of quite a different type. Have a look at this interesting sample:

AP4_Result AP4_StscAtom::WriteFields(AP4_ByteStream& stream)
{
  AP4_Result result;

  AP4_Cardinal entry_count = m_Entries.ItemCount();
  result = stream.WriteUI32(entry_count);

  for (AP4_Ordinal i=0; i<entry_count; i++) {
    stream.WriteUI32(m_Entries[i].m_FirstChunk);
    if (AP4_FAILED(result)) return result;
    stream.WriteUI32(m_Entries[i].m_SamplesPerChunk);
    if (AP4_FAILED(result)) return result;
    stream.WriteUI32(m_Entries[i].m_SampleDescriptionIndex);
    if (AP4_FAILED(result)) return result;
  }
  return result;
}

The checks 'if (AP4_FAILED(result)) return result;' in the loop are meaningless. The error is this: the 'result' variable is not changed when reading data from files.

This is the fixed code:

AP4_Result AP4_StscAtom::WriteFields(AP4_ByteStream& stream)
{
  AP4_Result result;
  AP4_Cardinal entry_count = m_Entries.ItemCount();
  result = stream.WriteUI32(entry_count);

  for (AP4_Ordinal i=0; i<entry_count; i++) {
    result = stream.WriteUI32(m_Entries[i].m_FirstChunk);
    if (AP4_FAILED(result)) return result;
    result = stream.WriteUI32(m_Entries[i].m_SamplesPerChunk);
    if (AP4_FAILED(result)) return result;
    result = stream.WriteUI32(m_Entries[i].m_SampleDescriptionIndex);
    if (AP4_FAILED(result)) return result;
  }
  return result;
}

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