Search code examples
cfat32fat

Storing result in variable gives strange results

I have a section of code that sometimes produces correct results. The only difference is I am storing the result in an intermediate variable.

The overall function signature is:

FS_FATEntry getFATEntryForCluster(FS_Cluster cluster, FS_Instance * fsi)

This works:

switch (fsi->type) {
    case FS_FAT12:
        if (cluster % 2)
            return ((*((uint16_t *)&FATSector[entOffset])) >> 4);
        else
            return ((*((uint16_t *)&FATSector[entOffset])) & 0x0FFF);
    case FS_FAT16:
        return (*((uint16_t *)&FATSector[entOffset]));
    case FS_FAT32:
        return ((*((uint32_t *)&FATSector[entOffset])) & 0x0FFFFFFF);
}

This does not: (note that FS_FATEntry is typedef'd as a uint32_t)

FS_FATEntry entry = 0xFFFFFFFF;
switch (fsi->type) {
    case FS_FAT12:
        if (cluster % 2)
            entry = ((*((uint16_t *)&FATSector[entOffset])) >> 4);
        else
            entry = ((*((uint16_t *)&FATSector[entOffset])) & 0x0FFF);
    case FS_FAT16:
        entry = (*((uint16_t *)&FATSector[entOffset]));
    case FS_FAT32:
        entry = ((*((uint32_t *)&FATSector[entOffset])) & 0x0FFFFFFF);
}
free(FATSector);
printf("Cluster %04X : %04X Entry\n", cluster, entry);
return entry;

When running the second piece of code, this is a snip of the output I get:

Cluster 00F9 : FB0FA0 Entry
Cluster 00FA : D0FC0FB Entry
Cluster 00FB : FD0FC0 Entry
Cluster 00FC : F0FE0FD Entry
Cluster 00FD : FF0FE0 Entry
Cluster 00FE : 11000FF Entry
Cluster 00FF : 1011000 Entry
Cluster 0100 : 3102101 Entry
Cluster 0101 : 1031021 Entry
Cluster 0102 : 5104103 Entry
Cluster 0103 : 1051041 Entry
Cluster 0104 : 7FFF105 Entry
Cluster 0105 : 107FFF1 Entry
Cluster 0106 : FFFF107 Entry
Cluster 0107 : FFFFFF1 Entry
Cluster 0108 : B10AFFF Entry
Cluster 0109 : 10B10AF Entry
Cluster 010A : D10C10B Entry
Cluster 010B : 10D10C1 Entry
Cluster 010C : F10E10D Entry
Cluster 010D : FFF10E1 Entry
Cluster 010E : 1110FFF Entry
Cluster 010F : 111110F Entry
Solution

  • The original code returns from each case, the new code falls through... did you intend to fall through on the switch ie not use break?