Optimize checksum calculation on verify

src/fileimpl.cpp

@@ -551,16 +551,36 @@ class Grouping
     struct zim_MD5_CTX md5ctx;
     zim_MD5Init(&md5ctx);
 
+    const int piece_size=1024;
+    unsigned char ch[piece_size];
     offset_type checksumPos = header.getChecksumPos();
     offset_type currentPos = 0;
+
     for(auto part = zimFile->begin();
         part != zimFile->end();
         part++) {
       std::ifstream stream(part->second->filename(), std::ios_base::in|std::ios_base::binary);
 
-      char ch;
-      for(/*NOTHING*/ ; currentPos < checksumPos && stream.get(ch).good(); currentPos++) {
-        zim_MD5Update(&md5ctx, reinterpret_cast<const uint8_t*>(&ch), 1);
+
+      while(currentPos < checksumPos-piece_size && stream.read(reinterpret_cast<char*>(ch),piece_size).good()) {
+        zim_MD5Update(&md5ctx, ch, piece_size);
+        currentPos+=stream.gcount();
+      }
+
+      // It reads and updates the checksum with the remaining amount of file
+      // when we reach the end of the file
+      if(stream.good()){
+        int remaining=checksumPos-currentPos;
+        stream.read(reinterpret_cast<char*>(ch),remaining);
+        zim_MD5Update(&md5ctx, ch, remaining);
+        currentPos+=stream.gcount();
+      }
+      // It updates the checksum with the remaining amount of part when we
+      // reach the end of the part or filesize is less than piece_size
+      else if(stream.gcount()>0){
+        int remaining=checksumPos<piece_size?checksumPos:stream.gcount();
+        zim_MD5Update(&md5ctx, ch, remaining);
+        currentPos+=remaining;
       }
       if (stream.bad()) {
         perror("error while reading file");
@@ -583,7 +603,6 @@ class Grouping
     {
       return false;
     }
-
     return true;
   }