FAT file system-read＆set

read sector number ThisFATSecNum (remember this is a sector number relative to sector 0 of the FAT volume). Assume this is read into an 8-bit byte array named SecBuff

If(FATType == FAT16)
    FAT16ClusEntryVal = *((WORD *) &SecBuff[ThisFATEntOffset]);
Else
    FAT32ClusEntryVal = (*((DWORD *) &SecBuff[ThisFATEntOffset])) & 0x0FFFFFFF;

set the contents of this same cluster

If(FATType == FAT16)
    *((WORD *) &SecBuff[ThisFATEntOffset]) = FAT16ClusEntryVal;
Else {
     FAT32ClusEntryVal = FAT32ClusEntryVal & 0x0FFFFFFF;
    *((DWORD *) &SecBuff[ThisFATEntOffset]) =
        (*((DWORD *) &SecBuff[ThisFATEntOffset])) & 0xF0000000;
    *((DWORD *) &SecBuff[ThisFATEntOffset]) =
        (*((DWORD *) &SecBuff[ThisFATEntOffset])) | FAT32ClusEntryVal;
}