opt: mdx -> avoid duplicated Adler-32 checksum in zlib decompression

.clang-tidy

@@ -26,6 +26,7 @@ Checks: >
   -google-default-arguments,
   -google-readability-casting,
   -hicpp-deprecated-headers,
+  -hicpp-no-array-decay,
   -misc-const-correctness,
   -misc-include-cleaner,
   -misc-non-private-member-variables-in-classes,

src/dict/mdictparser.cc

@@ -264,14 +264,12 @@ bool MdictParser::parseCompressedBlock( qint64 compressedBlockSize,
 
     case 0x02000000:
       // zlib compression
-      decompressedBlock = zlibDecompress( buf, size );
-
-      if ( !checkAdler32( decompressedBlock.constData(), decompressedBlock.size(), checksum ) ) {
-        gdWarning( "MDict: parseCompressedBlock: zlib: checksum does not match" );
+      decompressedBlock = zlibDecompress( buf, size, checksum );
+      if ( decompressedBlock.isEmpty() ) {
+        gdWarning( "MDict: parseCompressedBlock: zlib: failed to decompress or checksum does not match" );
         return false;
       }
       break;
-
     default:
       gdWarning( "MDict: parseCompressedBlock: unknown type" );
       return false;

src/dict/utils/decompress.cc

@@ -3,20 +3,21 @@
 #include <bzlib.h>
 #include <lzma.h>
 
-#define CHUNK_SIZE 2048
+using std::string;
 
-QByteArray zlibDecompress( const char * bufptr, unsigned length )
+static constexpr qsizetype CHUNK_SIZE = 2048;
+
+QByteArray zlibDecompress( const char * bufptr, unsigned length, uLong adler32_checksum )
 {
-  z_stream zs;
-  char buf[ CHUNK_SIZE ];
+  z_stream zs{};
   QByteArray str;
-  int res;
-  memset( &zs, 0, sizeof( zs ) );
+  int res     = Z_OK;
   zs.next_in  = (Bytef *)bufptr;
   zs.avail_in = length;
   res         = inflateInit( &zs );
 
   if ( res == Z_OK ) {
+    char buf[ CHUNK_SIZE ];
     while ( res != Z_STREAM_END ) {
       zs.next_out  = (Bytef *)buf;
       zs.avail_out = CHUNK_SIZE;
@@ -27,9 +28,7 @@ QByteArray zlibDecompress( const char * bufptr, unsigned length )
       }
     }
   }
-
-  inflateEnd( &zs );
-  if ( res != Z_STREAM_END ) {
+  if ( inflateEnd( &zs ) != Z_OK || res != Z_STREAM_END || ( adler32_checksum != 0 && zs.adler != adler32_checksum ) ) {
     str.clear();
   }
   return str;
@@ -37,7 +36,7 @@ QByteArray zlibDecompress( const char * bufptr, unsigned length )
 
 string decompressZlib( const char * bufptr, unsigned length )
 {
-  QByteArray b = zlibDecompress( bufptr, length );
+  QByteArray b = zlibDecompress( bufptr, length, 0 );
   return string( b.constData(), b.size() );
 }
 

src/dict/utils/decompress.hh

@@ -3,12 +3,11 @@
 #include <QByteArray>
 #include <string>
 
-using std::string;
+/// @param adler32_checksum  0 to skip checksum
+QByteArray zlibDecompress( const char * bufptr, unsigned length, unsigned long adler32_checksum );
 
-QByteArray zlibDecompress( const char * bufptr, unsigned length );
+std::string decompressZlib( const char * bufptr, unsigned length );
 
-string decompressZlib( const char * bufptr, unsigned length );
+std::string decompressBzip2( const char * bufptr, unsigned length );
 
-string decompressBzip2( const char * bufptr, unsigned length );
-
-string decompressLzma2( const char * bufptr, unsigned length, bool raw_decoder = false );
+std::string decompressLzma2( const char * bufptr, unsigned length, bool raw_decoder = false );