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#include "fat.h"
#include <stdio.h>
INTN
GetDrvNumOffset (
IN VOID *BootSector
)
{
FAT_BPB_STRUCT *FatBpb;
UINTN RootDirSectors;
UINTN FATSz;
UINTN TotSec;
UINTN DataSec;
UINTN CountOfClusters;
FatBpb = (FAT_BPB_STRUCT *) BootSector;
//
// Check FAT type algorithm from FAT spec
//
RootDirSectors = ((FatBpb->Fat12_16.BPB_RootEntCnt * sizeof(FAT_DIRECTORY_ENTRY)) +
(FatBpb->Fat12_16.BPB_BytsPerSec - 1)) / FatBpb->Fat12_16.BPB_BytsPerSec;
if (FatBpb->Fat12_16.BPB_FATSz16 != 0) {
FATSz = FatBpb->Fat12_16.BPB_FATSz16;
} else {
FATSz = FatBpb->Fat32.BPB_FATSz32;
}
if (FATSz == 0) {
fprintf (stderr, "ERROR: FAT: BPB_FATSz16, BPB_FATSz32 - 0, expected - Non-Zero\n");
return -1;
}
if (FatBpb->Fat12_16.BPB_TotSec16 != 0) {
TotSec = FatBpb->Fat12_16.BPB_TotSec16;
} else {
TotSec = FatBpb->Fat12_16.BPB_TotSec32;
}
if (TotSec == 0) {
fprintf (stderr, "ERROR: FAT: BPB_TotSec16, BPB_TotSec32 - 0, expected - Non-Zero\n");
return -1;
}
DataSec = TotSec - (
FatBpb->Fat12_16.BPB_RsvdSecCnt +
FatBpb->Fat12_16.BPB_NumFATs * FATSz +
RootDirSectors
);
CountOfClusters = DataSec / FatBpb->Fat12_16.BPB_SecPerClus;
if (CountOfClusters < FAT_MAX_FAT16_CLUSTER) {
return (INTN) ((UINTN) &FatBpb->Fat12_16.BS_DrvNum - (UINTN) FatBpb);
} else {
return (INTN) ((UINTN) &FatBpb->Fat32.BS_DrvNum - (UINTN) FatBpb);
}
}
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