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// gets the data at the given cluster offset
unsigned short GetClusterData( int cluster, char* fat )
{
	// the cluster number
	int realval = cluster;

	// return the data
	unsigned short data = ( fat[realval+1] << 8 ) | fat[realval];

	// return it
	return data;
}

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Hex editor: C9F0
OS swaps bytes...
Return from GetClusterData: FFC9

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Initializing Mattise...                                                        M
Floppy 1: 1.44MB 3.5in floppy 
Floppy 2: No floppy drive. 


Welcome to Mattise! 
Version 1.0 
Please enter your username and password to login... 
Username: isemat 
Password: ******* 
Reading sector 338... (the data area start is at 37) 

Reading cluster at offset 302 
EOF (ffff) 
Welcome, isemat! 
isemat@localhost> $  

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isemat@localhost> $ read MULTSECTTXT                                           M
Reading sector 336... (the data area start is at 37) 

Reading cluster at offset 300 
65481 (ffc9),Reading cluster at offset 65481 
How did we get pointed to a null entry? 
Hello, this is a file that spans two sectors. 

While most of the file reads in the Mattise 
filesystem read consecutive sectors, it is 
useful to be able to read more than one sector 
============================================== 
============================================== 
============================================== 
============================================== 
isemat@localhost> $ 

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multsect.txt ==> cluster 299

FAT12:

299 + ( 299 / 2 ) = 448.5
ThisFATSecNum = 1 + ( 0.8759765625 ); = 1
ThisFATEntOffset = 8759765625;

960 + ( 960 / 2 ) = 1440
FAtsecnum = 1 + 2.8125; = 3
fatentoffset = 8125;

(from fat doc)
    if (FATType == FAT12)
        FATOffset = N + (N / 2);    
/* Multiply by 1.5 without using floating point, the divide by 2 rounds DOWN */
    
    ThisFATSecNum = BPB_ResvdSecCnt + (FATOffset / BPB_BytsPerSec);
    ThisFATEntOffset = REM(FATOffset / BPB_BytsPerSec);


OR FAT16:

299 * 2 = 598
fat entry offset = remainder of 598 / 512 = 16796875 (86?)
fat sector number = 1 + 598 / 512 = 2.16... = 2

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// return the data
   unsigned short data = ( fat[realval+1] << 8 ) | fat[realval]; 

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// return the data
unsigned short data = ( fat[realval] << 8 ) | fat[realval+1];

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unsigned short GetClusterData( int cluster, unsigned short* fat){
	return fat[cluster];
}

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// gets the data at the given cluster offset
unsigned short GetClusterData( int cluster, char* fat )
{
	// return value
	unsigned short ret = 0;
	
	// sector block
	char fatblock[512];

	// the cluster entry value
	switch( myFloppy.FileSys )
	{
		case FAT12:
		
			printf( "FAT12_GetClusterData" );
			
			// get the offset
			unsigned short FATOffset = cluster + ( cluster / 2 );
			
			// sector number
			unsigned short ThisFATSecNum = myFloppy.BPB_RsvdSecCnt + ( FATOffset / myFloppy.BPB_BytsPerSec );
			
			// offset in the fat
			unsigned short ThisFATEntOffset = FATOffset % myFloppy.BPB_BytsPerSec;
			
			// tell
			printf( "Reading out of FAT sector %d at offset %d\n", ThisFATSecNum, ThisFATEntOffset );
			
			// read the block
			read_block( ThisFATSecNum, fatblock, 1 );
			
			// get it
			unsigned short FAT12ClustEntryVal = fatblock[ThisFATEntOffset];
			
			// odd/even
			if( cluster & 0x0001 )
			{
				FAT12ClustEntryVal = FAT12ClustEntryVal >> 4;
			}
			else
			{
				FAT12ClustEntryVal = FAT12ClustEntryVal & 0x0FFF;
			}
			
			// set the return
			ret = FAT12ClustEntryVal;
			
			break;
			
		default:
		
			// tell user we can't read anything else YET
			printf( "Only FAT12 is supported at the moment...\n" );
			
			break;
	}
	
	// return to caller
	return ret;
}

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File MultSect.txt is at sector 404-405 (checked)
Dir entry says at entry 273 (checked)
Adding 31 (start of data area) = 404 (correct)
Using 273 in GetClusterData: returns 7 (wrong)

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// gets the data at the given cluster offset
unsigned short GetClusterData( int cluster )
{
	// return value
	unsigned short ret = 0;
	
	// sector block
	char fatblock[512];

	// the cluster entry value
	switch( myFloppy.FileSys )
	{
		case FAT12:
		
			printf( "\nFAT12_GetClusterData" );
			printf( "\n" );
			
			// get the offset
			unsigned short FATOffset = cluster + ( cluster / 2 );
			
			// sector number
			unsigned short ThisFATSecNum = myFloppy.BPB_RsvdSecCnt + ( FATOffset / myFloppy.BPB_BytsPerSec );
			
			// offset in the fat
			unsigned short ThisFATEntOffset = FATOffset % myFloppy.BPB_BytsPerSec;
			
			// tell
			printf( "Reading out of FAT sector %d at offset %d\n", ThisFATSecNum, ThisFATEntOffset );
			
			// read the block
			read_block( ThisFATSecNum, fatblock, 1 );
			
			// get it
			unsigned short FAT12ClustEntryVal = * ( ( short* ) &fatblock[ThisFATEntOffset] );
			
			// odd/even
			if( cluster & 0x0001 )
			{
				FAT12ClustEntryVal = FAT12ClustEntryVal >> 4;
			}
			else
			{
				FAT12ClustEntryVal = FAT12ClustEntryVal & 0x0FFF;
			}
			
			// set the return
			ret = FAT12ClustEntryVal;
			
			break;
			
		default:
		
			// tell user we can't read anything else YET
			printf( "Only FAT12 is supported at the moment...\n" );
			
			break;
	}
	
	// return to caller
	return ret;
}

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void read_block( int block, char* data, int num );