#include <stdio.h>#include "msdos.h"extern int fd, dir_start, num_fat, fat_len, fat_error, fat_bits;extern unsigned char *fat_buf;/* * Puts a code into the FAT table.  Is the opposite of fat_decode().  No * sanity checking is done on the code.  Returns a 1 on error. */intfat_encode(num, code)unsigned int num;unsigned int code;{	unsigned int start;	if (fat_bits == 12) {		/*		 *	|    byte n     |   byte n+1    |   byte n+2    |		 *	|7|6|5|4|3|2|1|0|7|6|5|4|3|2|1|0|7|6|5|4|3|2|1|0|		 *	| | | | | | | | | | | | | | | | | | | | | | | | |		 *	| n+0.0 | n+0.5 | n+1.0 | n+1.5 | n+2.0 | n+2.5 |		 *	    \_____  \____   \______/________/_____   /		 *	      ____\______\________/   _____/  ____\_/		 *	     /     \      \          /       /     \		 *	| n+1.5 | n+0.0 | n+0.5 | n+2.0 | n+2.5 | n+1.0 |		 *	|      FAT entry k      |    FAT entry k+1      |		 */					/* which bytes contain the entry */		start = num * 3 / 2;		if (start <= 2 || start + 1 > (fat_len * MSECTOR_SIZE))			return(1);					/* (odd) not on byte boundary */		if (num % 2) {			*(fat_buf + start) = (*(fat_buf + start) & 0x0f) + ((code << 4) & 0xf0);			*(fat_buf + start + 1) = (code >> 4) & 0xff;		}					/* (even) on byte boundary */		else {			*(fat_buf + start) = code & 0xff;			*(fat_buf + start + 1) = (*(fat_buf + start + 1) & 0xf0) + ((code >> 8) & 0x0f);		}	}	else {		/*		 *	|    byte n     |   byte n+1    |		 *	|7|6|5|4|3|2|1|0|7|6|5|4|3|2|1|0|		 *	| | | | | | | | | | | | | | | | |		 *	|         FAT entry k           |		 */					/* which bytes contain the entry */		start = num * 2;		if (start <= 3 || start + 1 > (fat_len * MSECTOR_SIZE))			return(1);		*(fat_buf + start + 1) =  code / 0x100;		*(fat_buf + start) =  code % 0x100;	}	return(0);}/* * Write the FAT table to the disk.  Up to now the FAT manipulation has * been done in memory.  All errors are fatal.  (Might not be too smart * to wait till the end of the program to write the table.  Oh well...) */voidfat_write(){	int i, start, dups;	void disk_write();	if (fd < 0)		return;	start = dir_start - (fat_len * num_fat);	for (i=start; i<start+fat_len; i++)		disk_write((long) i, &fat_buf[(i-start)*MSECTOR_SIZE], MSECTOR_SIZE);	/*	 * Only duplicate the FAT table if no errors were detected	 */	if (!fat_error) {		dups = num_fat - 1;		while (dups--) {			start += fat_len;			for (i=start; i<start+fat_len; i++)				disk_write((long) i, &fat_buf[(i-start)*MSECTOR_SIZE], MSECTOR_SIZE);		}	}	return;}